Luminous Landscape Forum
Raw & Post Processing, Printing => Digital Image Processing => Topic started by: button on November 20, 2007, 12:57:13 pm
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Someone correct this if inaccurate, but here is something I just discovered:
Problem- I like to edit in 16 bit prophoto. However, when converting from prophoto RGB to sRGB in photoshop (for output to the web or for many offsite printers), the histogram will show the highlight and shadow clipping that occurs, forcing an "undo" of the sRGB conversion and a subsequent negative exposure compensation in prophoto, to allow headroom in sRGB.
Solution- Open files in camera RAW (RAW files, jpegs, whatever) and set the editing preference (in the bottom center of the screen) to 8 bit sRGB. Correct the exposure and all other global adjustments in camera RAW that you wish. When done, change the preference to 16 bit prophoto- watch the histogram become more compressed as this happens. Now, open the image in photoshop from camera RAW (which will be 16 bit prophoto), and apply whatever local adjustments you want- masks, hue/saturation, whatever. When done, convert back to 8 bit sRGB (if output is for the web or an offsite printer without ICC profile), or assign the printer's profile if available. Watch the histogram jump back to what you saw in camera RAW under the initial 8 bit sRGB settings. This will help prevent blown highlights (and crushed shadows) in your prints.
Any critique or comments appreciated.
John
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hello John,
I really don't understand what you are exactly doing...but maybe it is only a problem I have.
What I do understand is that conversion from Prophoto to sRGB may be difficult with some images, because of the smaller gamut.; maybe you could explain it in a different way.
Pieter Kers
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hello John,
I really don't understand what you are exactly doing...but maybe it is only a problem I have.
What I do understand is that conversion from Prophoto to sRGB may be difficult with some images, because of the smaller gamut.; maybe you could explain it in a different way.
Pieter Kers
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I don't understand either.
And I don't understand the issues of converting from ProPhoto RGB to sRGB. Well sure, its a lot smaller color space, you're going to use a RelCol conversion to map out of gamut colors into gamut, there's clipping. That's going to have to happen, you're starting out with a gallon of water and trying to pour it into a cup. The recipe (in this case, say the internet) calls for a cup. What's the problem?
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The problem I encountered is that the histograms whose exposures I pushed to the right while editing in prophoto in photoshop looked balanced in that color space, but showed significant clipping when converted to sRGB for offsite printing. The highlights that clipped on the histogram looked blown out on my prints. My idea is to try to prevent this from happening by setting the exposure value in sRGB in camera RAW to give myself a preview of the maximum luminance headroom available for an sRGB print (preview a prophoto image in a program that's not color aware, such as Faststone, and see how crappy it is). The reason to then switch to 16 bit prophoto is to allow more editting leway in photoshop.
I'm assuming that the switch from sRGB to prophoto in camera RAW is a non-destructive one that acutally reassings the color space, as opposed to starting off in prophoto in photoshop, switching to sRGB (which will chop off the out of gamut colors in a relative colormetric conversion) to check for clipping, and switching back to prophoto to edit (which will expand the now reduced color gamut, potentially causing posturization during editting). Yes, you can simply switch from prophoto to sRGB in photoshop to preview the histogram and then "undo" it, but this becomes a problem after multiple edits and is cumbersome. I haven't tried the "assign profile" command in photoshop, which may obviate these steps.
Please let me know if this makes sense.
John
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The problem I encountered is that the histograms whose exposures I pushed to the right while editing in prophoto in photoshop looked balanced in that color space, but showed significant clipping when converted to sRGB for offsite printing.
Forget the histogram for the time being. Just as two color spaces have differing numbers, they may have differing histograms. How's the color appearance?
The highlights that clipped on the histogram looked blown out on my prints.
From simply going ProPhoto RGB to sRGB (and then to what output color space)? I've yet to see this. What output device and why are you converting from ProPhoto RGB to sRGB to output color space? Why are you not going ProPhoto RGB to output color space?
I'm assuming that the switch from sRGB to prophoto in camera RAW is a non-destructive one that acutally reassings the color space, as opposed to starting off in prophoto in photoshop, switching to sRGB (which will chop off the out of gamut colors in a relative colormetric
Its not non destructive. You're converting color spaces right? And you're altering the data so there's data loss. What would make Camera Raw handle the conversions any differently than Photoshop (it doesn't other than it has to do yet another conversion into a linear encoded ProPhoto space before it can do any further adjustments or conversions).
I haven't tried the "assign profile" command in photoshop, which may obviate these steps.
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There's no reason to use Assign Profile, that would really hose the color appearance.
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I don't understand either.
And I don't understand the issues of converting from ProPhoto RGB to sRGB. Well sure, its a lot smaller color space, you're going to use a RelCol conversion to map out of gamut colors into gamut, there's clipping. That's going to have to happen, you're starting out with a gallon of water and trying to pour it into a cup. The recipe (in this case, say the internet) calls for a cup. What's the problem?
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I have discussed this problem before in some threads, but can't remember where. Here is an example of a highly saturated red flower which will not fit into sRGB, but which will fit into ProPhotoRGB.
sRGB without adjustment shows strong clipping of the reds
[attachment=3933:attachment]
One can decrease the exposure and eliminate the clipping, but the image becomes dark
[attachment=3934:attachment]
Or one can use ProPhotoRGB and get the full gamut
[attachment=3935:attachment]
Now if you want to convert to sRGB for the web, you will have to decrease saturation in the reds, either by manual editing or using a profile with perceptual rendering. This rendering does not exist for matrix profiles such as sRGB, but a forum member informed me of another profile for this purpose, but I can't remember the name. It used lookup tables.
Bill
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I have discussed this problem before in some threads, but can't remember where. Here is an example of a highly saturated red flower which will not fit into sRGB, but which will fit into ProPhotoRGB.
I'd expect this to be the case with lots of images. They don't fit into the puny sRGB space. That's why we have larger color spaces like ProPhoto RGB.
One can decrease the exposure and eliminate the clipping, but the image becomes dark
Obviously not a good solution....
Or one can use ProPhotoRGB and get the full gamut
Fine.
Now if you want to convert to sRGB for the web, you will have to decrease saturation in the reds, either by manual editing or using a profile with perceptual rendering. This rendering does not exist for matrix profiles such as sRGB, but a forum member informed me of another profile for this purpose, but I can't remember the name. It used lookup tables.
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Yes, it will be useful when V4 profiles of working spaces with perceptual tables are more widely available although having such tables alone doesn't at all guarantee that the problem is solved.
What you can do is convert and edit the sRGB version (or just live with it, doesn't seem to be a big deal), or soft proof the ProPhoto RGB image as sRGB and edit then convert.
So what's the real downside you see just doing the conversion from ProPhoto to sRGB, knowing doing this has to toss a lot of colors because you're demanding a document in a smaller color space. How is this different from converting from ProPhoto RGB to some CMYK process where everything gets less saturated or using a soft proof with a printer profile whereby the new color appearance isn't the same as the original? That's a tradeoff we all have to experience moving from a large gamut color space based on a display to a smaller gamut color space based on possibility a print.
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Its not non destructive. You're converting color spaces right? And you're altering the data so there's data loss. What would make Camera Raw handle the conversions any differently than Photoshop (it doesn't other than it has to do yet another conversion into a linear encoded ProPhoto space before it can do any further adjustments or conversions).
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Andrew,
Correct me if I'm wrong, but I think the bit depth and colour space choices offered in the menu under the image in CR 4.x are essentially instructions for rendering the image. If one were to select say 8 bit sRGB and render the image on that basis, that is all one would end-up with in Photoshop; hence from a pure Photoshop perspective one has lost 7 bits of bit depth and the gamut between pro-Photo and sRGB. BUT, if one were to revert to the raw file and change those settings back to 16bit ProPhoto, is it not the case that all the raw data is still there allowing one to make that reversion?
Now, turning to the OPs issue, his problem starts with his description of the problem. Sure, if the image begins life in 16 bit ProPhoto he needs to get into 8 bit sRGB for the web. But Photoshop has excellent tools for doing this seemlessly. He should do all his image editing in 16 bit ProPhoto; then use Photoshop's tools to prepare his images for the web. All the stuff on my website was done as follows, starting from 16 bit ProPhoto:
Image Size with resamplingto 96 ppi and 600~800 pixels on the large dimension; interpolation bi-cubic sharper;
PK Output Sharpen for the web; (set opacity to taste);
Convert to sRGB with RelCol Intent and BPC on;
Convert Mode to 8 bit;
Save for Web in JPEG format, 60% quality, Optimized, with embedded sRGB profile.
That menu almost always works. Where gamut clipping still appears to be problematic, it is necessary to experiment with Perceptual Intent, and/or reduce the saturation of the offending colour group.
No other gymnastics in the raw converter are really needed.
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That menu almost always works. Where gamut clipping still appears to be problematic, it is necessary to experiment with Perceptual Intent, and/or reduce the saturation of the offending colour group.
No other gymnastics in the raw converter are really needed.
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Mark,
As I understand the problem, there is currently no perceptual rendering when one is converting from ProPhotoRGB to sRGB. It is always RelCol, even though Photoshop gives no warning that the intent is not available.
The OP's technique is to temporarily switch to sRGB in the ACR preferences, perform the editing in ACR so that the gamut fits (apparently with exposure or perhaps saturation), and then change back to ProPhotoRGB before rendering the image. Since the gamut after the edit does not exceed that of sRGB, one could have rendered the image into sRGB and then converted to ProPhotoRGB in Photoshop. As Andrew pointed out, decreasing exposure is not a good idea, since the image darkens.
Bill
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Andrew,
Correct me if I'm wrong, but I think the bit depth and colour space choices offered in the menu under the image in CR 4.x are essentially instructions for rendering the image.
Yes. By rendering, I'd prefer to do this from the Raw data of course.
If one were to select say 8 bit sRGB and render the image on that basis, that is all one would end-up with in Photoshop; hence from a pure Photoshop perspective one has lost 7 bits of bit depth and the gamut between pro-Photo and sRGB.
Seems right to me. The potential of higher bit depth and gamut based on the same rendering settings.
BUT, if one were to revert to the raw file and change those settings back to 16bit ProPhoto, is it not the case that all the raw data is still there allowing one to make that reversion?
Sure.
Now, turning to the OPs issue, his problem starts with his description of the problem. Sure, if the image begins life in 16 bit ProPhoto he needs to get into 8 bit sRGB for the web. But Photoshop has excellent tools for doing this seemlessly. He should do all his image editing in 16 bit ProPhoto; then use Photoshop's tools to prepare his images for the web.
Right. Now the question is, do you render both versions, one ProPhoto RGB, one sRGB (lots more work) or just work in ProPhoto, convert to sRGB? And as I asked, it seems that working on a high bit, wide gamut master is essentially something we do all the time for iterations that go out to various printing devices so why is the web any different here? Yes, we have less tables to work with in our profiles but I don't know that is necessarily going to solve a problem I'm not sure exists. Since every profile building product creates its own idea of an ideal Perceptual rendering, this could get more messy, not less so.
The main question remains. When you convert from ProPhoto RGB to sRGB, does this conversion produce issues with the subsequent color appearance? And if so, is it impossible or real difficult to correct this? The times I've done this, more recently out of Lightroom to make web galleries, I haven't found any real problems here with the subsequent color appearance of the images. I'm either looking at them on a display, or a print and the print is always different and that's why I soft proof the images and if necessary, try to make minor corrections for that final output media.
An sRGB version versus a ProPhoto RGB version, especially considering most people are working with an sRGB output device (the display) seem nearly identical visually to me. There is a far bigger disconnect in the ProPhoto version and the output version on print. We've dealt with that for years. They are just vastly different output mediums.
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The main question remains. When you convert from ProPhoto RGB to sRGB, does this conversion produce issues with the subsequent color appearance? And if so, is it impossible or real difficult to correct this? The times I've done this, more recently out of Lightroom to make web galleries, I haven't found any real problems here with the subsequent color appearance of the images. I'm either looking at them on a display, or a print and the print is always different and that's why I soft proof the images and if necessary, try to make minor corrections for that final output media.
An sRGB version versus a ProPhoto RGB version, especially considering most people are working with an sRGB output device (the display) seem nearly identical visually to me. There is a far bigger disconnect in the ProPhoto version and the output version on print. We've dealt with that for years. They are just vastly different output mediums.
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Re your main question above, from my experience the answer is "generally not". And when it does, correcting it in PS is not that big a deal for the reason you state. In the workflow I described, all those steps are performed before Lightroom picks up the images to make a gallery. To start from scratch in my case, the images are optimized as much as possible in 16 bit ProPhoto in CR4.x, then residual work is done in PS to get them to print properly. Then to repurpose them for the web I go through the steps I outlined in my previous post, perhaps with a Curves tweak or two because of the re-purposing; then I pick the JPEGs up in Lightroom to create the galleries. In this workflow Lightroom is being used mainly to generate the macromedia code and the display format, not to re-adjust colour and luminosity. Hence if the OP does not have LR and doesn't want to buy it, but has some other application for generating the web galleries, the PS workflow will serve his purposes too. And I agree with you completely - it is much more challenging to work a print from ProPhoto than a web-purposed image for the reason you suggest.
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Mark,
As I understand the problem, there is currently no perceptual rendering when one is converting from ProPhotoRGB to sRGB. It is always RelCol, even though Photoshop gives no warning that the intent is not available.
The OP's technique is to temporarily switch to sRGB in the ACR preferences, perform the editing in ACR so that the gamut fits (apparently with exposure or perhaps saturation), and then change back to ProPhotoRGB before rendering the image. Since the gamut after the edit does not exceed that of sRGB, one could have rendered the image into sRGB and then converted to ProPhotoRGB in Photoshop. As Andrew pointed out, decreasing exposure is not a good idea, since the image darkens.
Bill
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Bill,
When you "Convert to Profile" in the same dialog box where you select sRGB, down below you can select the Rendering Intent and can select Perceptual, RelCol, etc.
I wasn't recommending to decrease exposure for dealing with OOG - rather decreasing the saturation of the OOG colour(s), if the Perceptual Intent doesn't look after it sufficiently.
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When you "Convert to Profile" in the same dialog box where you select sRGB, down below you can select the Rendering Intent and can select Perceptual, RelCol, etc.
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Actually, for transforms between working spaces, there's really only one intent at play, Relative Colormetric...there are some ICC v4 profiles out there that DO have perceptual intents...there's a v4 sRGB beta space. See: [a href=\"http://www.color.org/srgbprofiles.xalter]sRGB v4 Preference.ICC Profile[/url] but then of course, you really should only use v4 profiles with other v4 profiles...and I don't think there is a v4 Pro Photo profile.
So, when you do a Convert to Profile command, it doesn't matter WHAT intent you choose, you'll end up getting RelCol.
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Actually, for transforms between working spaces, there's really only one intent at play, Relative Colormetric...there are some ICC v4 profiles out there that DO have perceptual intents...there's a v4 sRGB beta space. See: sRGB v4 Preference.ICC Profile (http://www.color.org/srgbprofiles.xalter) but then of course, you really should only use v4 profiles with other v4 profiles...and I don't think there is a v4 Pro Photo profile.
So, when you do a Convert to Profile command, it doesn't matter WHAT intent you choose, you'll end up getting RelCol.
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Jeff, if that's the case, why does PS give us the option to select the three others?
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Actually, for transforms between working spaces, there's really only one intent at play, Relative Colormetric...there are some ICC v4 profiles out there that DO have perceptual intents...there's a v4 sRGB beta space. See: sRGB v4 Preference.ICC Profile (http://www.color.org/srgbprofiles.xalter) but then of course, you really should only use v4 profiles with other v4 profiles...and I don't think there is a v4 Pro Photo profile.
So, when you do a Convert to Profile command, it doesn't matter WHAT intent you choose, you'll end up getting RelCol.
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Jeff,
Very interesting. What would happen if you used the new profile with a non-V4 ProPhoto profile? I guess one could download the new profile and give it a try.
Bill
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Jeff, if that's the case, why does PS give us the option to select the three others?
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To screw with your heads...
:~)
Actually, the Convert to Profile SHOULD dim out non-available rendering intents, but that logic hasn't been added to the app...yet.
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Very interesting. What would happen if you used the new profile with a non-V4 ProPhoto profile?
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I have no idea...I haven't had time to test the v4 profiles...(been kinda busy)
:~)
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It looks as though the OP has assumed that the changes reflected in the histogram when converting from ProPhoto to sRGB are also reflected in the appearance of the converted image on screen.
What springs to mind here is the fact that no monitor can fully display the gamut of ProPhoto. Most monitors are closer to the sRGB gamut are they not, with just a few really expensive monitors being able to display the full gamut of ARGB, which is not as wide as ProPhoto.
Here's an image I took recently in poor lighting for the purpose of checking out the noise reducing capability of the 'stacking' feature in CS3E and the auto-alignment capability with 7 hand-held shots at 1/20th sec and ISO 1600.
There's no doubt that the histogram is radically altered when converting to sRGB, but the appearance of the image seems to remain the same.
[attachment=3937:attachment] [attachment=3938:attachment]
You will notice that even Buddhist statues are now paying homage to the histogram .
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John,
I noticed the same and I am doing the same thing you do. Now, whether what we are doing makes sense is a different matter, hence your totally legitimate call for discussion. Unfortunately, it seems that your question provoked mostly smarty-pants comments. Some posters either pretend they do not understand, or did not bother to read carefully your post (and I exclude here those who really have no idea what you are talking about). Yet they try to win the argument by barking up the wrong tree (i.e, by refuting something you did not say). Hopefully, further discussion will return to your original question.
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It looks as though the OP has assumed that the changes reflected in the histogram when converting from ProPhoto to sRGB are also reflected in the appearance of the converted image on screen.[a href=\"index.php?act=findpost&pid=154598\"][{POST_SNAPBACK}][/a]
Actually, I do not notice a change in the appearance of an image when I switch between pro photo and sRGB, despite the histogram changes. I think this observation strikes at the heart of the problem- when I soft proof, I don't see a histogram change, and so I don't yet know what the limits of the output space are. Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping. I "Preview" the image in sRGB in camera RAW because an sRGB image seems to yield decent results from most offsite RGB commercial printers that don't provide ICC profiles (Walgreens, etc). If I could preview with an ICC profile, I'd use that instead if I wanted to print the image from that printer.
John
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Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping.
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Uh, are you actually using "assign"? If so, this is wrong...are you referring to using soft proof or Convert to Profile?
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... or using a profile with perceptual rendering. This rendering does not exist for matrix profiles such as sRGB, but a forum member informed me of another profile for this purpose, but I can't remember the name. It used lookup tables.
Bill
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PhotoGamutRGB
[a href=\"http://www.photogamut.org/E_Index.html]http://www.photogamut.org/E_Index.html[/url]
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To screw with your heads...
:~)
Actually, the Convert to Profile SHOULD dim out non-available rendering intents, but that logic hasn't been added to the app...yet.
[a href=\"index.php?act=findpost&pid=154591\"][{POST_SNAPBACK}][/a]
Thanks Jeff. I assume the word "yet" means it's one of those minor issues they know about and will get around to fixing in some future release.
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PhotoGamutRGB
http://www.photogamut.org/E_Index.html (http://www.photogamut.org/E_Index.html)
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Yes, this is the profile. Thanks.
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Jeff,
Very interesting. What would happen if you used the new profile with a non-V4 ProPhoto profile? I guess one could download the new profile and give it a try.
Bill
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I have no idea...I haven't had time to test the v4 profiles...(been kinda busy)
:~)
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Apparently, the answer is in ICC White Paper 26, but I have not been able to locate this paper on the ICC web site. Can anyone help?
"Advice for caution
Ideally the ICC v4 profile should not be combined with ICC v2 profiles. If that is unavoidable, see the intermediate-level ICC White Paper 26 'Using the sRGB_v4_ICC_preference.icc profile' for additional information and recommendations."
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Actually, I do not notice a change in the appearance of an image when I switch between pro photo and sRGB, despite the histogram changes. I think this observation strikes at the heart of the problem- when I soft proof, I don't see a histogram change, and so I don't yet know what the limits of the output space are. Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping. I "Preview" the image in sRGB in camera RAW because an sRGB image seems to yield decent results from most offsite RGB commercial printers that don't provide ICC profiles (Walgreens, etc). If I could preview with an ICC profile, I'd use that instead if I wanted to print the image from that printer.
John
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Softproofing does not change the histogram. It changes the appearance of the image on the display to mimic what the print will look like. It is like a filter which says "if you configure me this way, this is what I'll do to the appearance of your image", without actually doing it. Therefore because the image itself has not been altered, the histogram remains the same. However, if you were to actually convert to another colour space, you are altering the image and the change should show on the histogram.
Now, the rest of your post concerns what one could call "best practice". Normally, best practice is to work your images conserving the most data possible so that some time in the future you will have everything that was originally available to repurpose the image. If you render the raw file into an 8 bit sRGB working space and build a whole slew of adjustments on that basis because it is suitable for a Costco printer today, should the time come that you want to do something else with that image which can take advantage of more bit depth and a wider colour palette, you would need to go back to the raw file and start processing all over again by rendering the raw file in - say - 16 bit ProPhoto and redoing all the subsequent work. It is easier - usually - to start with the maximum information, then scale it down to the specific purpose at the moment using adjustment layers, as these can be repurposed in the future. The image you take to Costco would be a flattened file resaved with another name so you don't lose anything from your "Gold Master". If, however, you have a very high degree of confidence that you will never need anything more than an sRGB working space from this file, you could begin the process in sRGB and save yourself some steps. But I would recommend retaining the image in 16-bit mode till the very last point when you need to make a conversion that does not support 16 bit depth, because you have much less risk of damaging the image by eidting in 16 bit.
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Jeff, if that's the case, why does PS give us the option to select the three others?
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Well two (you can use an Absolute Colorimetric intent). Absolute and Relative share the same table and for all practical purposes are identical except for how white is handled. And Abs would look pretty awful in nearly all such cases.
On one hand, it would be useful for Adobe to dim Perceptual and Saturation in these cases but since picking them doesn't do anything but force RelCol, I guess they did this to make it 'easier'? And when more V4 profiles come about, they would have to rewire everything anyway. If someone toggles such matrix conversions between say Saturation and Perceptual and really feels one is better than the other visually, they deserve the RelCol rendering <g>.
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What springs to mind here is the fact that no monitor can fully display the gamut of ProPhoto.
Nor any image. Its important to realize that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math. In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision. I only point this out as now that we are seeing displays that get close to, match and exceed Adobe RGB (1998), people are now asking about the same capability for ProPhoto RGB. Ain't going to happen. We need really large synthetic color spaces for certain tasks but that doesn't mean all the colors defined are useful or in this case even visible.
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Uh, are you actually using "assign"? If so, this is wrong...are you referring to using soft proof or Convert to Profile?
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My mistake, Jeff. I should have said "convert." I haven't experimented with "assign profile yet," as I'm not sure how to use it.
Mark, I agree with you. The "costco" files are ones that I use for that printer only- I save all my masters separately.
John
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Actually, I do not notice a change in the appearance of an image when I switch between pro photo and sRGB, despite the histogram changes. I think this observation strikes at the heart of the problem- when I soft proof, I don't see a histogram change, and so I don't yet know what the limits of the output space are. Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping. I "Preview" the image in sRGB in camera RAW because an sRGB image seems to yield decent results from most offsite RGB commercial printers that don't provide ICC profiles (Walgreens, etc). If I could preview with an ICC profile, I'd use that instead if I wanted to print the image from that printer.
John
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John,
If you want to see the histogram in the printer color space, I think you would have to convert to that color space (convert, not assign). When you are soft proofing, the data are in the original color space and the histogram will be for that space, not the destination space. To view out of gamut colors, you can use the gamut warning in Photoshop soft proofing, but that does not tell you how far the image is out of gamut.
If you want to use the Costco profiles from Drycreek.com, you have to convert to the profile with the desired rendering intent. If you assign the profile, you have not changed the numbers in the file, but only how they are interpreted by Photoshop.
If you want to compare the gamut of the file to that of the printer, you need appropriate software such as ColorThink (expensive) or Norman Koren's GamutVision (more reasonable). Then you can see which colors are out of gamut and how far they are out of gamut.
sRGB works reasonably well for the Costco printers (which may be Nortisu or Fuji Frontier, depending on the store), because the gamut of these printers is not significantly larger than the sRBG gamut. If you look at the interactive gamut display on Drycreek.com and compare sRGB with the Noritsu 3101 and Crystal Archive paper, you will see that the printer can handle some yellows and cyans that are out of the sRGB gamut. If you use aRGB, a few yellows in the Costco gamut still can't be represented.
The newer inkjet printers have a considerably larger gamut, and it is best to use ProPhotoRGB when outputting to them. Modern digital cameras can capture colors well outside of the aRGB and sRGB gamut, and such out of gamut colors can be contained in rather innocuous appearing images, as Jeff shows with a ColorThink plot on p. 12 of the ACR book.
Bill
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Its important to realize that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math.
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mmm can you explain how sRGB is a synthetic colour space as opposed to a real colour space.
Are the sRGB primaries not based on actual phosphors as specified in CCIR 709??
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mmm can you explain how sRGB is a synthetic colour space as opposed to a real colour space.
Are the sRGB primaries not based on actual phosphors as specified in CCIR 709??
sRGB is a synthetic color space but based on the behavior of (at the time) a CRT display with P22 phosphors and the spec was even based on the ambient conditions under which this theoretical display resided in. But its synthetic in that its based on simple math specifications (gamma, white point and chromaticity values).
From the father of sRGB (posted a very long time ago on the ColorSync list):
1. sRGB is not base on "standard" "typical" or any other type of PC monitor,
but is directly derived from the HDTV standard ITU-R BT.709/2
2. sRGB does represent not only average PC monitors, but is within the
factory tolerances of almost all CRTs on the market today, including Barco
professional CRTs. This is due to the shared family set of P22 phosphors
which almost all CRTs use today. While this "family" of P22 phosphors has
some differences between manufacturers, these differences fall within each
manufacturer's factory tolerances. Saying that sRGB chromaticities are
"quite small" is simply saying that CRT phosphors in general are quite
small.
3. While the 2.2 gamma was directly derived from HTDV, it has been
independently verified by Sony, Barco and others to represent the native
physical state of CRTs today. It is also very close to the native human
perceptual lightness scale when viewing CRTs. This combination makes this
gamma the optimal for CRTs to physically operate at. This also goes a long
way in explaining the compatibility with Windows and PCs in general since
these systems have not imposed any arbitary or proprietary system
adjustments.
4. The white point again is derived directly from the television industry
and is the standard is televisions and also in many aspects of photography.
Achieving a bright enough D50 white point to comfortably adapt to continues
to be a technical challenge for CRT vendors.
Michael Stokes
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sRGB is a synthetic color space but based on the behavior of (at the time) a CRT display with P22 phosphors and the spec was even based on the ambient conditions under which this theoretical display resided in. But its synthetic in that its based on simple math specifications (gamma, white point and chromaticity values).
From the father of sRGB (posted a very long time ago on the ColorSync list):
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Are the primaries of sRGB not within the CIE x,y chromaticity diagram and their coordinates are that of current CRT phosphors, within the specified tollerences, (and the same as LCD filters) hence making it a 'real' colour space as opposed to ProPhoto (ROMM RGB - Reference Output Medium Metric RGB) which has two of its primaries CIE x,y coordinates out side the spectral locus, thus making it a hypothetical or 'synthetic' colour space.
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Are the primaries of sRGB not within the CIE x,y chromaticity diagram and their coordinates are that of current CRT phosphors, within the specified tollerences, (and the same as LCD filters) hence making it a 'real' colour space as opposed to ProPhoto (ROMM RGB - Reference Output Medium Metric RGB) which has two of its primaries CIE x,y coordinates out side the spectral locus, thus making it a hypothetical or 'synthetic' colour space.
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Its a matter of semantics. Is it real because a CRT display can hit it? Sure. Of course, if you calibrate said CRT, will it exactly match the sRGB spec's, down to the exact location of the primaries? Probably not. Is it synthetic because its manufacturer is based on a theoretical device (one based on a real world device but not one we know for a fact exactly defines this space)? I'd say yes to that.
When you output hundreds of patches and measure them to build a printer profile, I'd say that is absolutely a 'real world' profile.
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Solution- Open files in camera RAW (RAW files, jpegs, whatever) and set the editing preference (in the bottom center of the screen) to 8 bit sRGB. Correct the exposure and all other global adjustments in camera RAW that you wish. When done, change the preference to 16 bit prophoto- watch the histogram become more compressed as this happens. Now, open the image in photoshop from camera RAW (which will be 16 bit prophoto), and apply whatever local adjustments you want- masks, hue/saturation, whatever. When done, convert back to 8 bit sRGB (if output is for the web or an offsite printer without ICC profile), or assign the printer's profile if available. Watch the histogram jump back to what you saw in camera RAW under the initial 8 bit sRGB settings. This will help prevent blown highlights (and crushed shadows) in your prints.
Any critique or comments appreciated.
Kinda stupid and pointless IMO. There is no point at all in using ProPhoto as an editing space when you're dumbing down all the colors to fit into sRGB before the image leaves the RAW converter. If you're going to keep all colors within sRGB, then just use sRGB as your editing space and be done with it. But that's a really stupid approach given that most printers can print at least some colors outside sRGB, and as printer and display technology is improving the proportion of usable gamut outside sRGB is getting larger all the time.
A much better approach is to stay in ProPhoto, edit the image until it looks the way you want it to, and then save that as the master copy. When necessary, perform selective desaturation or whatever other edits you need to do to fit the image into a particular device's output gamut, convert the image to the device's profile, and then save that as a copy of the image. That way as print technology improves, you can go back to the master copy of the image and make a less-compromised version of the image for a new printer without having to go all the way back to the original RAW.
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A much better approach is to stay in ProPhoto, edit the image until it looks the way you want it to, and then save that as the master copy.
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MMM you guys are missing something here.
You cant edit in Prophoto until you 'it looks the way you want' because you are viewing in sRGB space (or the monitor space which is near to sRGB). so really the visual editing of ProPhoto is not a good idea.
The next colourspace outside of sRGB that manufacturers can now achieve is AdobeRGB as with the Eizo ColorEdge CG221.
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MMM you guys are missing something here.
You cant edit in Prophoto until you 'it looks the way you want' because you are viewing in sRGB space (or the monitor space which is near to sRGB). so really the visual editing of ProPhoto is not a good idea.
The next colourspace outside of sRGB that manufacturers can now achieve is AdobeRGB as with the Eizo ColorEdge CG221.
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Well yes and no. Yes, you can see an awful lot of the image which is falling into sRGB on an sRGB display. The colors that fall outside, the very saturated colors no but its not like the image you see on an sRGB display next to an Adobe RGB display look hugely different, they don't (I have such a setup). Does a spectral gradient look more saturated in ProPhoto RGB on the Adobe RGB display then the sRGB? Yes. Does the relationship of the image look so different I don't have any idea which is correct? Nope. I have to soft proof the image anyway to an output device which is vastly different in terms of gamut and as importantly, dynamic range. Then I have to view the reflective print and try to mentally compare it to an emissive display. Had to do this with chrome film and prints, chrome film and ink on paper from a CMYK press. Is this a prefect WYSIWYG? No, but its pretty close.
So, do you squash the colors in a working space to fit your display so you can see everything? Sure, if your only output is that display. But most of us have to output our files to all kinds of differing devices. Devices that far exceed sRGB. Then the question becomes, do you keep the colors you can output, outside the sRGB display? For most, the answer is yes.
We're dealing with, and always will deal with different reference media. Unless your life is really simple, you're just using a display as an output device, you have to live with these differences. One approach then is to throw away colors you can't see but can output. The other is output the colors you can't see but can output.
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Another thing that you don't mention is where does the image gamut lie.
If most of your imaging fall inside the sRGB space then use sRGB if not use Adobe RGB if not use
Prophoto - which covers the gamut of Real world surface colours.
But as for workflows.
If you want to VISUALLY edit colours, we are at the moment restricted to editing in monitor space sRGB or AdobeRGB.
These space will include some output spaces but not all. For those image gamuts outside the display gamuts there is NO VISUAL editing and we must 'go by the numbers'.
Eg image captured in sRGB, viewed in Photoshop on a AdobeRGB compliant monitor and converted to ISO Coated v2 CMYK.
The file can be viewed and visually edited in both inputspace and outputspace (if needed).
If the image gamut is outside that of AdobeRGB and ROMM encoding is used and the destination outputspace is for eg ISO Coated v2 CMYK, then any editing is done by numbers and the results evaluated after printing. This is fine if you are an experienced repro operator but not for the average (and even a lot of pros) photographers to work.
Most are making a VISUAL assessment of the file prior to saving or output.
The new sRGBv4.0 along with the other ICC v4.0 input and output profiles will make for a better sRGB workflow for most workflows.
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If you want to VISUALLY edit colours, we are at the moment restricted to editing in monitor space sRGB or AdobeRGB.
Again, yes and no. If you're editing based on a soft proof of an output device, you're going to be all over the map here with what does and doesn't fall within the gamut of your display, sRGB or otherwise.
These space will include some output spaces but not all. For those image gamuts outside the display gamuts there is NO VISUAL editing and we must 'go by the numbers'.
What numbers? You're editing for an Epson 3800 on luster paper, a SWOP press, a Lambda, or any other output device you want to mention. The ICC profiles you use to soft proof provide the output numbers but do you know what to aim for? What's middle gray for a Pictrography 4500 supposed to be? Or a Canon ipf 5000 running fine art paper?
The file can be viewed and visually edited in both inputspace and outputspace (if needed).
But again, even with something like SWOP, there are colors that fall outside an sRGB display so we're back to square one here (and square one isn't really a big deal).
The new sRGBv4.0 along with the other ICC v4.0 input and output profiles will make for a better sRGB workflow for most workflows.
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How so?
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You keep saying yes and no to some of my remarks without providing a a proper answer.
I dont think you are really understanding the point I am trying to make which was initially in reference to the comment
"that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math'
You also state
'In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision.'
mmm I think most people would challenge you on that one!
Colours outside the HVS????
I think what you mean is that ProPhoto is a colour encoding space which includes coordinates NOT COLOURS outside the HVS.
Same can be said of CIEXYZ and CIELAB.
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You keep saying yes and no to some of my remarks without providing a a proper answer.
Because your statements are black and white and there's more to it than that.
"that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math'
All the RGB working space are synthetic color spaces.
You also state
'In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision.'
mmm I think most people would challenge you on that one!
All you have to do is look at a CIE chromaticity diagram to see this. There are at least two primaries that fall outside the spectrum locus.
http://www.luminous-landscape.com/tutorial...photo-rgb.shtml (http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml)
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You also state 'In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision.' mmm I think most people would challenge you on that one!
Colours outside the HVS????
You betcha! Challenge accepted, since it is so easy:
http://www.luminous-landscape.com/tutorial...photo-rgb.shtml (http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml)
Look at Figure. 3b (about half way down) ProPhoto RGB "actually exceeds it (visible spectrum) in the deep greens and deep blues. What this means is that colours can be pushed into areas which can neither be seen nor reproduced, producing very nasty looking results within the visible spectrum. User beware."
It is worth reading the rest of the article too. - Angst
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Look at Figure. 3b (about half way down) ProPhoto RGB "actually exceeds it (visible spectrum) in the deep greens and deep blues. What this means is that colours can be pushed into areas which can neither be seen nor reproduced, producing very nasty looking results within the visible spectrum. User beware."
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Well I don't know if user beware is compulsory, we don't want to scare people because its necessary to have such large working spaces.
Forgive my standard copy and paste, but it puts these kinds of color spaces into perspective.
I call it, Gamut mismatch (fitting round pegs in square holes)
It IS true that the wider the granularity in a color space, the harder it is to handle subtle colors. This is why wide gamut displays that can't revert to sRGB (current LCD technology doesn't allow this.) are not ideal for all work (ideally you need two units).
There are way, way more colors that can be defined in something like ProPhoto RGB than you could possibly output, true. But we have to live with a disconnect between the simple shapes of RGB working space and the vastly more complex shapes of output color spaces to the point we're trying to fit round pegs in square holes. To do this, you need a much larger square hole. Simple matrix profiles of RGB working spaces when plotted 3 dimensionally illustrate that they reach their maximum saturation at high luminance levels. The opposite is seen with print (output) color spaces. Printers produce color by adding ink or some colorant, working space profiles are based on building more saturation by adding more light due to the differences in subtractive and additive color models. To counter this, you need a really big RGB working space like ProPhoto RGB again due to the simple size and to fit the round peg in the bigger square hole. Their shapes are simple and predictable. Then there is the issue of very dark colors of intense saturation which do occur in nature and we can capture with many devices. Many of these colors fall outside Adobe RGB (1998) and when you encode into such a space, you clip the colors to the degree that smooth gradations become solid blobs in print, again due to the dissimilar shapes and differences in how the two spaces relate to luminance.
So, since we're dealing with simple shapes here (synthetic RGB working spaces), you have to move the primaries father apart, in the case of ProPhoto RGB, that means two are outside human gamut. So yes, you can define colors you can't see, let alone work with colors that fall outside your display gamut. Its just the compromise we have to deal with working with large gamut encoding color spaces. But I don't know that we need to be too scared of this (user beware now is probably appropriate)
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You also state 'In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision.' mmm I think most people would challenge you on that one!
Colours outside the HVS????
You betcha! Challenge accepted, since it is so easy:
http://www.luminous-landscape.com/tutorial...photo-rgb.shtml (http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml)
Look at Figure. 3b (about half way down) ProPhoto RGB "actually exceeds it (visible spectrum) in the deep greens and deep blues. What this means is that colours can be pushed into areas which can neither be seen nor reproduced, producing very nasty looking results within the visible spectrum. User beware."
It is worth reading the rest of the article too. - Angst
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yes ive looked at that article.
first the author states referring to figure 3b
'Below is a more traditional colour gamut chart. The large horseshoe shaped area shows the LAB colour space.'
The horseshoe does not show the CIELAB colourspace. It shows the CIE x,y chromaticity diagram. This is derived from CIEXYZ colour space.
The author also fails to mention that ProPhoto (ROMM RGB) primaries were chosen to encompass the gamut of real world surface colours without using unnecessary encoding space ie coordinates outside the visual locus.
Again there are NO COLOURS outside the spectral Locus!!!
For a reference on Prophoto (ROMM RGB)
look at the chapter
Implementation of Device-Independent Colour At Kodak
by Kevin SPAULDING and Edward GIORGIANNI
Colour Engineering- Achieving Device Independent Colour
Eds Phil Green and Lindsay MacDonald.
2002 John Wiley and Sons
Chichester
England
or go to kodak and search ROMM two pdf by by Kevin SPAULDING
[a href=\"http://search.kodak.com/?pq-locale=en_US&global=en&q=ROMM]http://search.kodak.com/?pq-locale=en_US&global=en&q=ROMM[/url]
Far more informative and correct.
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The horseshoe does not show the CIELAB colourspace. It shows the CIE x,y chromaticity diagram. This is derived from CIEXYZ colour space.
Two primaries do fall outside the spectrum locus. Here's an illustration made in ColorThink Pro in 3D. You can easily see the spectrum locus and the red shape of ProPhoto RGB and its clear it falls outside this plot. ColorThink allows you to plot using Yxy or Luv, it plots this over the spectrum locus.
Are you on a Mac? Double click on a profile to open the ColorSync utility.
Select New Utility Window, then click on the Profile button.
Select ProPhoto RGB and you can view the gamut in LAB (have Show Spectrum on), look at the plot. Now toggle to Yxy, to see the plot, which clearly shows the primaries falling outside the locus.
This isn't earth shattering news either.
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If you read my posts carefully you will find that I have not disputed the fact that two of the primaries lie outside the spectral locus.
What I have been saying is that there are NO COLOURS outside the Spectral Locus. It is only encoding space and should be called as such.
Using phrases such as "COLOURS we cant see' is wrong and very misleading and adds confusion to the reader.
Its a matter of semantics. Very important in colour science.
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What I have been saying is that there are NO COLOURS outside the Spectral Locus. It is only encoding space and should be called as such.
Its a matter of semantics. Very important in colour science.
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Yeah OK, I'll buy that. We can't see 'colors' outside the spectrum locus so, I'm OK saying they are not colors (heck, if I can't see them, they are invisible).
Note we can define numerically a 'color' in ProPhoto RGB we can't see, there's no reason to argue that. But is that a color?
If a tree falls in the forest and no one is around... never mind. <G>
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No. We can't numerically define a colour we cant 'see'.
We can define a coordinate in a colour encoding space that is outside the spectral locus but it is not
quote' a colour we cant see'
This implies that 'colour' exists outwith human perception.
Again the use of 'invisible colours' is wrong.
Using terms like the above will only help to cloud peoples understanding of colour science and colour reproduction etc.
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No. We can't numerically define a colour we cant 'see'.
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Well I think I'm going to have to disagree. In Photoshop, we can define the two primary colors (example R0/G0/B255) in ProPhoto RGB. But such a color would fall outside the locus. And here lies somewhat of an issue.
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No. We can't numerically define a colour we cant 'see'.
Rubbish. We numerically difine and measure all sorts of things we can't see. Human perception is not a good yardstick for defining whether or not something exists. Infrared and ultraviolet light exists, 100KHz sounds exist, and so do neutrons. All of those thing have been precisely defined, and can be measured with the right equipment. But none of us are capable of perceiving such things directly with our senses. Given that, I think it's a bit narrow-minded to define a "color" as something perceivable by human vision, as the exact range of wavelengths that any given human eye can perceive varies from person to person, and then there's the whole issue of color-blind people...
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Quote 'In Photoshop, we can define the two primary colors (example R0/G0/B255) in ProPhoto RGB. But such a color would fall outside the locus. And here lies somewhat of an issue.'
No you are defining a coordinate in a colour encoding space NOT a COLOUR!
Its a number and nothing but a number. You keep referring to it as a colour though, when its outside the HVS.
Why?
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No you are defining a coordinate in a colour encoding space NOT a COLOUR!
Its a number and nothing but a number. You keep referring to it as a colour though, when its outside the HVS.
Why?
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Everything we do on a computer is a number. That this number defines what you don't want me to call a color (because its outside human gamut) doesn't make it much different from the perspectives of the user, the application where you define the color or the numbers does it?
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You keep referring to it as a colour though, when its outside the HVS. Why?
Because insisting that a "color" be defined as something perceivable by human vision is arbitrary, and ignores the reality that not all humans perceive "color" in the same way (color blindness for example) and not all humans visually perceive the exact same frequency range of light waves anyway. In a dark room, I can faintly see the emissions of some IR remote control LEDs (same with the IR data port on some Palms & laptops), and can tell when a button is being pressed or data is being transmitted. Many people cannot. Is IR a color then, or not? I can see it, poorly, yes, but some IR falls within my range of visual perception. At what point does a "color" become a "color" instead of a mathematical construct? When 10% of the population can visually perceive it? 20%? 50%? 99?% Who put you in the position of authority to decide?
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Because insisting that a "color" be defined as something perceivable by human vision is arbitrary, and ignores the reality that not all humans perceive "color" in the same way (color blindness for example) and not all humans visually perceive the exact same frequency range of light waves anyway. In a dark room, I can faintly see the emissions of some IR remote control LEDs (same with the IR data port on some Palms & laptops), and can tell when a button is being pressed or data is being transmitted. Many people cannot. Is IR a color then, or not? I can see it, poorly, yes, but some IR falls within my range of visual perception. At what point does a "color" become a "color" instead of a mathematical construct? When 10% of the population can visually perceive it? 20%? 50%? 99?% Who put you in the position of authority to decide?
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Good point!
Well this at least is a civil and I have to say interesting conversation. Is a color someone can't see a color or not?
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Maybe we should all be using visible color when defining colors within the locus?
I'm pinging a color scientist on this. It will be interesting to hear what they have to say about this (science or semantics)?
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Maybe we should all be using visible color when defining colors within the locus?
Even that is measuring with a rubber ruler given the person-to-person variations in what wavelengths of light are visually perceivable and how they are perceived.
Is an 30KHz tone a sound? Some humans can hear frequencies that high to some extent, and bats and dogs can do so fairly easily. But most humans can't. Does that mean it isn't a "sound"?
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Even that is measuring with a rubber ruler given the person-to-person variations in what wavelengths of light are visually perceivable and how they are perceived.
Visible color as defined by the CIE, not necessarily everyone on the planet. The Standard Observer if you will.
We've all seen the plots of frequency of electromagnet energy that define visible light, or the spectrum locus. I'm suggesting visible colors are defined by such general statements, stuff outside such plots are colors, but simply not known to be visible to humans. Of course, YMMV.
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Even that is measuring with a rubber ruler given the person-to-person variations in what wavelengths of light are visually perceivable and how they are perceived.
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I think the way in which the rubber ruler issue gets resolved is by scientific method - e.g. to replicate visual experiments amongst a large number of volunteers, such that with a large enough sample of observers of the same phenomina the sample of responses becomes representative, reliable averages and their variances are calculated and that defines the standard, is it not?
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You can apply such methods to determine what percentage of the population can perceive a particular wavelength of light, but you still have the problem of defining what the cutoff percentage is before defining whether a color is "visible" or not. That's where the arbitrariness comes in. Do you define something as "visible" when 10% of the test subjects can see it, 25%, 50%, or 90%? No matter which of those values you choose to draw the boundary line, there will still be enough exceptions that using that boundary as a criteria for defining yes/no "colorness" attribute to a given point in a color space is pointless.
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Yes, at some point judgments about signifigance need to be made, but how did the CIE approach this one back in 1931?
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As far as I can see (ouch: pun) from following this discussion, the only definition of color that is precisely defined is one that requires the word "color" to be applied only to those visual sensations that can be seen by all persons. Since that must include those who are totally blind, clearly the set of "colors" is the empty set.
Ergo, there are no colors!
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In a dark room, I can faintly see the emissions of some IR remote control LEDs (same with the IR data port on some Palms & laptops), and can tell when a button is being pressed or data is being transmitted. Many people cannot. Is IR a color then, or not? I can see it, poorly, yes, but some IR falls within my range of visual perception.
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Very interesting!
Which LEDs are these, and what are their IR wavelength range. Can you specify the manufacture.
I would like to measure them as see exactly what spectral radiation they are emitting.
What is probably happening is that the LED is giving off both IR and visible wavelengths.
also
Quote
'I'm pinging a color scientist on this. It will be interesting to hear what they have to say about this (science or semantics)?'
MMM should be very interesting
also
" Visible color as defined by the CIE, not necessarily everyone on the planet. The Standard Observer if you will. "
Is this discussion not about ROMM a colour encoding space derived from CIE colorimetry??
and finally
"Given that, I think it's a bit narrow-minded to define a "color" as something perceivable by human vision,..."
What or how would you define 'colour' then? This will be most interesting!
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As far as I can see (ouch: pun) from following this discussion, the only definition of color that is precisely defined is one that requires the word "color" to be applied only to those visual sensations that can be seen by all persons. Since that must include those who are totally blind, clearly the set of "colors" is the empty set.
Ergo, there are no colors!
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And my tech editor (and a color scientist who I asked) agrees with you sort of (and papa)
Color, is a perceptual property. So if you can't see it it's not a
color. Color is not a particular wavelength of light. It is a
cognitive perception that is the end result of the excitation of
photoreceptors followed by retinal processing and ending in the
visual cortex. We define colors based on perceptual experiments.
A coordinate in a "colorspace" outside the spectrum locus is not a
color. We often refer to these as "imaginary colors" but this is by
and large also erroneous (you can't map an imaginary color from one
colorspace to another as the math (and experimental data) for each
colorspace breaks down outside the spectrum locus.
No one sees IR. Most IR LEDs have minor output in visible wavelengths
as well as IR.
Karl Lang
I learn something new and useful every day!
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Hi
Thanks Digital Dog and Jonathan Wienke for a stimulating and well mannered discussion.
Next!
Cheers, Papa v2.0
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Color, is a perceptual property. So if you can't see it it's not a
color.
Well, I'm willing to concede that Karl Lang knows more about the subject than I do. But I still have one nagging question: If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?
As an individual with a fairly common form of color-blindness (generally called "red-green"), I know that there are portions of the "visible" spectrum that are not visible to my eyes. Are those colors, or are they perhaps "semi-colors"?
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Color, is a perceptual property. So if you can't see it it's not a
color.
Well, I'm willing to concede that Karl Lang knows more about the subject than I do. But I still have one nagging question: If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?
As an individual with a fairly common form of color-blindness (generally called "red-green"), I know that there are portions of the "visible" spectrum that are not visible to my eyes. Are those colors, or are they perhaps "semi-colors"?
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I think the essential point here is that color is a subjective phenomenon. It has no objective reality specifically as a color. It has an objective reality as an electromagnertic wave length, or as a mathematical construct.
It is claimed that some species of birds, colorful birds of paradise, can see another primary in the ultraviolet region. We have no way of knowing what such a 4th primary would look like. In fact we have no way of knowing if one person's sensation of say red is the same as another person's. We usually refer to such subjective responses as qualia.
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I think the essential point here is that color is a subjective phenomenon. It has no objective reality specifically as a color. It has an objective reality as an electromagnertic wave length, or as a mathematical construct.
It is claimed that some species of birds, colorful birds of paradise, can see another primary in the ultraviolet region. We have no way of knowing what such a 4th primary would look like. In fact we have no way of knowing if one person's sensation of say red is the same as another person's. We usually refer to such subjective responses as qualia.
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[a href=\"http://en.wikipedia.org/wiki/Color_vision]Wikipedia[/url] has an interesting article on color vision. If you look at the graph of the spectral response of the human eye, you will see that there is a gap between the S (blue) and M (green) spectra. There was an interesting article in Scientific American a couple of years ago discussing the evolution of these sensors. Some animals (birds I think) have a fourth sensor in this gap, and human precursors apparently did also, but it was lost in evolution. Some mammals are dichromats and others have no color vision.
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If person A (not blind) can see a certain wavelength of light, but person B (also not blind) cannot, is there still a color here?
There is color for person A and no color for person B. Karl's point (and now that I think of it, Bruce Fraser once said), color is something that happens in our brains. The brain of person B doesn't 'see' the color, thus there isn't a color.
At the end of the day, it doesn't matter. We're just battery food in the Matrix <g>
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For those interested in the biology of color perception, a great introduction can be found in 'Vision and Art: The Biology of Seeing', by Margaret S. Livingstone. The author is a Harvard neurobiologist, but the book is very simply written and beautifully illustrated.
Dario
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'Wikipedia'...
is probably the last place you want to quote from, if one wants to enter any sensible discussion or to be taken seriously.
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'Wikipedia'...
is probably the last place you want to quote from, if one wants to enter any sensible discussion or to be taken seriously.
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A recent comparison by the highly respected UK journal [a href=\"http://news.bbc.co.uk/1/hi/technology/4530930.stm]Nature[/url] of Wikipedia to Encyclopedia Britannica showed that Wikipedia was about as accurate on scientific subjects as the more established publication. In recent threads Wikipedia has been quoted by Andrew Rodney, Jeff Schewe and others who expect to be taken seriously.
For serious scholarly publications the author would most likely refer to primary sources and not an encyclopedia, and Wikipedia is not allowed to be referenced by many universities. However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.
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Wikipedia (http://en.wikipedia.org/wiki/Color_vision) has an interesting article on color vision. If you look at the graph of the spectral response of the human eye, you will see that there is a gap between the S (blue) and M (green) spectra. There was an interesting article in Scientific American a couple of years ago discussing the evolution of these sensors. Some animals (birds I think) have a fourth sensor in this gap, and human precursors apparently did also, but it was lost in evolution. Some mammals are dichromats and others have no color vision.
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It's seems there's quite a bit of ongoing research taking place regarding these additional color sensitivities. It's not only some birds of the feathered variety who can see a fourth primary but some birds of the homo sapien variety also.
Refer this article at [a href=\"http://ray.tomes.biz/b2/index.php/a/2007/06/21/p147]http://ray.tomes.biz/b2/index.php/a/2007/06/21/p147[/url]
In fact, it seems that some birds of the feathered variety can not only see a fourth primary between the current blue and green wavelengths, but a fifth primary in the ultra-violet region. They are pentachromats.
Simplified, we have some colorblind men who are dichromats; most of us who are trichromats; the occasional woman who is a tetrachromat, and some species of birds and butterflies who are pentachromats.
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Please shoe me where the article is in serious error.
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[a href=\"http://en.wikipedia.org/wiki/Color_vision]http://en.wikipedia.org/wiki/Color_vision[/url]
Wikipedia states
'three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.'
you can see colour with only two things!
As in the case of emmissive light or blackbody radiation - source and detector
See what I mean about Wikipedia
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http://en.wikipedia.org/wiki/Color_vision (http://en.wikipedia.org/wiki/Color_vision)
Wikipedia states
'three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.'
you can see colour with only two things!
As in the case of emmissive light or blackbody radiation - source and detector
See what I mean about Wikipedia
[a href=\"index.php?act=findpost&pid=156928\"][{POST_SNAPBACK}][/a]
Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
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Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
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That's what I thought, Eric, but wasn't able to express it so succinctly.
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no
using the eye as the detector
colour can be seen from a blackbody radiator (two things) and also from a surface reflection (three things)
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no
using the eye as the detector
colour can be seen from a blackbody radiator (two things) and also from a surface reflection (three things)
Given that the vast majority of objects in the universe are not luminous in the visible spectrum, I think that characterizing the Wikipedia article as "inaccurate" is pedantic nitpicking. Incomplete (for not listing the an exception for luminous objects) perhaps, but not inaccurate.
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Nonsense. You'r simply saying that two of the three might be the same thing. If I'm looking at a light source, the light source is also the sample.
[a href=\"index.php?act=findpost&pid=156959\"][{POST_SNAPBACK}][/a]
A further riposte to Papa:
If you want to nit-pick even further, color is a perception that occurs in the brain. The eye is only a sensor that transmits tri-stimulus color information to the brain, where it is processed, resulting in the perception of color. The eye may be working properly in a comatose person, but there will be no perception of color.
However, when presenting information to a general audience, some simplifications need to be made or else the presentation may be overwhelming. Thus, I am not considering the opponency theory of color, which would only muddle the issue further.
"Small minds are much distressed by little things. Great minds see them all but are not upset by them."
Francois de La Rochefoucauld
French author & moralist (1613 - 1680)
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Given that the vast majority of objects in the universe are not luminous in the visible spectrum,
[a href=\"index.php?act=findpost&pid=156981\"][{POST_SNAPBACK}][/a]
what do you mean by 'not luminous in the visible spectrum'
but to get back to the point of
"However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.'
Three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.
The above statement is not true.
I have identified an error as requested.
And JBANES you are correct in that the eye is only the detector and the "colour" is formed in the visual cortext. I should have descried the combination as
1. source and 2. observer
or 1. source 2. sample (reflective or transmissive) and 3. observer
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"However, the article I cited above is perfectly suitable for this forum. Please shoe me where the article is in serious error.'
Three things are needed to see color: a light source, a detector (e.g. the eye) and a sample to view.
The above statement is not true.
I have identified an error as requested.
And JBANES you are correct in that the eye is only the detector and the "colour" is formed in the visual cortext. I should have descried the combination as
1. source and 2. observer
or 1. source 2. sample (reflective or transmissive) and 3. observer
[a href=\"index.php?act=findpost&pid=157026\"][{POST_SNAPBACK}][/a]
Is this a serious error? I think not.
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depends on your point of view (excuse the pun)! ho ho
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To extend the argument to its logical confusion, papa v2.0 quoted "JBANES" when the correct author of the quote is actually "bjanes", therefore, nothing papa v2.0 says has any credibility whatsoever...
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To extend the argument to its logical confusion, papa v2.0 quoted "JBANES" when the correct author of the quote is actually "bjanes", therefore, nothing papa v2.0 says has any credibility whatsoever...
[a href=\"index.php?act=findpost&pid=157173\"][{POST_SNAPBACK}][/a]
That's what I call a "serious error".
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You can apply such methods to determine what percentage of the population can perceive a particular wavelength of light, but you still have the problem of defining what the cutoff percentage is before defining whether a color is "visible" or not. That's where the arbitrariness comes in. Do you define something as "visible" when 10% of the test subjects can see it, 25%, 50%, or 90%?
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What if you applied the arbritary 10% cut off with regard to something more easily measurable such as human height, would that mean those at the 5% percentile at either end don't exist/aren't human?
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What if you applied the arbritary 10% cut off with regard to something more easily measurable such as human height, would that mean those at the 5% percentile at either end don't exist/aren't human?
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Some of you guys sure like tying yourselves in knots .
The question, 'is a particular color visible?' is very vague and therefore can only have a vague answer based on unstated assumptions. Make the question more precise by adding by whom, then you can get a more precise and meaningful answer.
'Is this color visible by 70% of the human population, by 10% of the human population, by 90% of a particular species of bird etc etc ?', then you can get a meaningful answer, if you do your research.
Part of the confusion is due to the colloqial and metaphorical way we use language where it is expected that the reader or listener will understand what we have missed out or not clearly defined. For example, the question itself, "Does the ProPhoto Color Space contain colors which cannot be seen by 'normal' humans?" implies that colors have an objective existence. But we know this is not true.
To avoid this untrue implication, perhaps the question should be something like, "Does the ProPhoto color space define the position of frequencies within the electromagnetic spectrum which cannot be seen by most humans?" One could then go on to make the question even more cumbersome by defining what is meant by 'seen".
Sometimes one just has to use a bit of common sense, ya know.
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as we say in scotland
best you thats see a loon that canna swim
and see them drown
with oot the chance of of oiffering your arm
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as we say in scotland
best you thats see a loon that canna swim
and see them drown
with oot the chance of of oiffering your arm
[a href=\"index.php?act=findpost&pid=157398\"][{POST_SNAPBACK}][/a]
No, papa! You cannot shed light on this by quoting gibberish.
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No, papa! You cannot shed light on this by quoting gibberish.
[a href=\"index.php?act=findpost&pid=157417\"][{POST_SNAPBACK}][/a]
Funny because what ive read here by the so called experts turns out to be quality gibberish.
including yourself!
"Does the ProPhoto color space define the position of frequencies within the electromagnetic spectrum which cannot be seen by most humans?"
need i say more
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"Does the ProPhoto color space define the position of frequencies within the electromagnetic spectrum which cannot be seen by most humans?"
[a href=\"index.php?act=findpost&pid=157452\"][{POST_SNAPBACK}][/a]
Yes.
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Yes.
[a href=\"index.php?act=findpost&pid=157467\"][{POST_SNAPBACK}][/a]
Thanks!
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need i say more
[a href=\"index.php?act=findpost&pid=157452\"][{POST_SNAPBACK}][/a]
no.
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sorry guys
beep your expert on the last qoute
"Does the ProPhoto color space define the position of frequencies within the electromagnetic spectrum which cannot be seen by most humans?"
no it does not
come on guys you are letting the side down
lets go back to colour fundamentals
Grassmans law of additivity
the pro photo or ROMM ' Primaries' only exist in a manor which has been evolved from the CIE COLORMETRY of CIEXYZ colour space
in order to define the human visual spectrum we need to develop a primary that is not ' visible ' but a mathematical constraint for that colour space
hence the CIE XYZ space
the coordinates of these spaces include the colours we ca see and also empty space as well!
there are no colors outside the human visual system!!!!!!!!
we are having a discussion on ProPhoto
so lets get there!
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Hunt calls color a "percept". This elegant term does convey that a whole processing chain is involved in creating a percept, including not least an original active perception. Note also that practical color science is increasingly factoring the conditions under which the perception is taking place into mathematical description of the "color" perceived.
As a sidenote, I'd dispute that the eye is only a "sensor" for tristimulus information, if only because some women are quadrichromats (and there are rods, and there is a substantial amount of compression and therefore processing going on, and and ...)
Edmund
A further riposte to Papa:
If you want to nit-pick even further, color is a perception that occurs in the brain. The eye is only a sensor that transmits tri-stimulus color information to the brain, where it is processed, resulting in the perception of color. The eye may be working properly in a comatose person, but there will be no perception of color.
However, when presenting information to a general audience, some simplifications need to be made or else the presentation may be overwhelming. Thus, I am not considering the opponency theory of color, which would only muddle the issue further.
"Small minds are much distressed by little things. Great minds see them all but are not upset by them."
Francois de La Rochefoucauld
French author & moralist (1613 - 1680)
[a href=\"index.php?act=findpost&pid=157002\"][{POST_SNAPBACK}][/a]
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As a sidenote, I'd dispute that the eye is only a "sensor" for tristimulus information, if only because some women are quadrichromats (and there are rods, and there is a substantial amount of compression and therefore processing going on, and and ...)
Edmund
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Quick reference to the [a href=\"http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=303800]OMIM[/url] web site will show that human color vision is quite complex. A pertinent quote is, "...distinguished 2 types of normal color vision according to 'greenpoint,' i.e., the point at which the subject sees pure green, and 2 types according to 'bluepoint.' He presented the following genetic hypothesis: males can be of either G1/B1, G1/B2, or G2/B2; females can be of 6 genotypes."
From a brief reading of the description of the female tetrachromats, it would appear that rather than having an entirely new photo pigment, they merely may have two slightly different copies of the gene for the green pigment. One could debate is this is true tetrachromaticity.
Since the green gene is on the X-chromosome, us males can have only one copy of each gene, but there are differences among "normal" males in their green photo pigments, and all men may not see this color in quite the same way. Of course, color blind males see color quite differently. Some women could have more than 4 and up to 6 different photo pigments.
Any generalization concerning human psychology and physiology is likely to be a simplification, but many times a useful simplification for our comprehension of the processes. This leads to a veritable goldmine for nit-pickers . However, current color theory is based on the tri-stimulus theory and the camera makers have not yet accommodated these female tetrachromats, and I do not think that these advances have been incorporated into the standard CIE observer database.
Hopefully, the authority of this reference will satisfy even Papa V2.0.