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Author Topic: Color management myths and misinformation video  (Read 84926 times)

digitaldog

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Re: Color management myths and misinformation video
« Reply #440 on: September 22, 2014, 01:03:01 pm »

The blue balls show banding on the higher luminance ball and the lower luminance ball is very dark. The Epson profiles are apparently not as good as your custom profile. What do you think?
Just printed a test using the supplied Epson profile for glossy. I concur with your observations! I think it is a profile issue. If you can build a custom profile, that might be the way to go, this test file shows the 'issues' with the Epson Glossy profile as far as I'm concerned.
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Lundberg02

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Re: Color management myths and misinformation video
« Reply #441 on: September 23, 2014, 01:31:02 am »

They are very different Blue, 60 in top, 4 in bottom(every other line with my reader is zero in the bottom image).
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Lundberg02

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Re: Color management myths and misinformation video
« Reply #442 on: September 23, 2014, 01:35:01 am »

From EarthBound Light "What About ProPhoto RGB?" among many others:

It is the only one of the three though that encompasses the entire gamut of the Epson printer shown. sRGB severely clips the Epson gamut in the cyan to green region (bottom left) and yellow-orange region (top). Adobe RGB can still clip some very saturated yellows but does cover all the greens, and green is a very important color being in the middle of the visual spectrum and very prevalent in nature. It seems tempting then to use ProPhoto RGB in order to not lose that area of yellow. But if we do, we have to accept the fact that we also will be encompassing colors we can't even see, never mind print.
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digitaldog

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Re: Color management myths and misinformation video
« Reply #443 on: September 25, 2014, 10:35:44 am »

From EarthBound Light "What About ProPhoto RGB?" among many others:

It is the only one of the three though that encompasses the entire gamut of the Epson printer shown. sRGB severely clips the Epson gamut in the cyan to green region (bottom left) and yellow-orange region (top). Adobe RGB can still clip some very saturated yellows but does cover all the greens, and green is a very important color being in the middle of the visual spectrum and very prevalent in nature.

Someone on another forum suggested I test Adobe RGB (1998) to the Epson using the Gamut Test File. Here's what I see:

Blue/Cyan bkgnd of fish is more saturated with better detail with ProPhoto RGB. Due to the Epson's wider gamut than Adobe RGB in cyan's, this is quite a visible difference and the ProPhoto RGB image is purer (the Adobe RGB blue is less cyan which isn't quite correct IMHO). The big disconnect is the colored fabric in terms of what I see in 'shadow detail'. I talk about why I think this is happening in part 3 of the video in terms of how a really wide gamut working space allows dark but very saturated colors to better map to the output profile. This isn't so much about saturation as color difference and thus detail! The ProPhoto shadows of saturated colors seem more open and sharper! It's about how the colors differentiate when converted to the output profile which I illustrate with a 3D gamut map.

Bill's 14 Balls:
The differences here are significant! Again, Adobe RGB doesn't cut it. The Cyan ball shows banding more than ProPhoto, it's shifting in color (like I see on the fish bkgnd image). Magenta isn't that much different, a bit smoother in ProPhoto. Red suffers in Adobe RGB, there are magenta shifts of banding. Green is much smoother in ProPhoto, looks like a sphere, in Adobe, way too much banding. And blue suffers in Adobe RGB much like the Cyan ball.

What I suspect is that the 3880 gamut is just much larger in blue/cyan without even having to open ColorThink and plot the two gamuts.

So for this test image, to my eyes, Adobe RGB is just too small a gamut for this device. A Lightjet, Lambda, Frontier, really old ink jet, maybe good enough, maybe no difference on the print.

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Jim Kasson

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Re: Color management myths and misinformation video
« Reply #444 on: September 25, 2014, 11:56:02 am »

...we have to accept the fact that we also will be encompassing colors we can't even see, never mind print.

<pedantic mode on> If we can't see it, it's not a color. <pedantic mode off> ;)

Jim

digitaldog

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Re: Color management myths and misinformation video
« Reply #445 on: September 25, 2014, 12:12:42 pm »

But if we do, we have to accept the fact that we also will be encompassing colors we can't even see, never mind print.
And the same is true for sRGB! This is another red herring like "I can't use a working space who's gamut is larger than my display". As if the output profile doesn't produce colors (yes actual colors we can see) that can't be seen on the display with or without soft proofing. They fall outside display gamut (even those that can produce Adobe RGB (1998) gamut).
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #446 on: October 03, 2014, 03:24:41 pm »

I haven't been following this thread (and with a zillion pages I won't be going through it!) so I apologize if this point has already been made.

Anyway, it's this: the gamut of the test image is huge.  Here is a dEab map of the image compared to the Epson 9900 with Canson Photo Hi Gloss paper (a combination that is about as good as it gets at this stage).  As you can see the most of the image gamut exceeds the printer gamut by a dE of 20, going to a max of 140:



and here is a 3D Lab map showing the vectors in a Relative Colorimetric mapping from the image to the printer gamut:



In other words, the image is WAY outside both the printer gamut and obviously WAY, WAY outside the gamut of smaller color spaces like Adobe RGB or sRGB.

What that means is that if you follow Andrew's print test, what you will be doing is a Relative Colorimetric conversion to sRGB, which will clip the hell out of the image, resulting in the desaturation and flattening that you see.  This has nothing to do with the printing, it has simply to do with the fact that a) sRGB is MUCH too small to contain the image's gamut, and b) the conversion from ProPhoto to sRGB is a Relative Colorimetric mapping by definition, and RC mappings clip colors rather than compress them, so that what you end up with are flattened areas and color shifts.

All that this test demonstrates is that small working spaces can only contain the gamut of less saturated images, while larger working spaces can contain the gamut of more saturated images.

There is no competent color management expert that I am aware of who would not advise against converting an image from a large working space to a small working space before printing (unless you are sure that the smaller working space can fully, or nearly fully, contain the image's gamut ... and even then the possible benefits of doing the conversion are subtle and probably outweighed by the potential damage to the image).

sRGB, Adobe RGB or ProPhoto RGB each have their place: if you only want to use one color space and mostly print then ProPhoto is clearly a good choice; if you only output to the web then sRGB is the obvious choice because that is currently the only supported color space on the web.  Adobe RGB is not a bad compromise, and it conveniently fits the newer wide-gamut monitors.  If you are printing in black and white it doesn't matter what of the working spaces you use.  And so on ...

Robert
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ErikKaffehr

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Re: Color management myths and misinformation video
« Reply #447 on: October 03, 2014, 03:43:47 pm »

Hi Robert,

Two questions:

  • Has not both Adobe RGB and sRGB has passed it's best before date, now that we have 4K with Rec. 2020 colour space?
  • Is there a need for a new colour space needed for 8-bit representation of the Rec 2020 colour space?

I don't pretend to be an expert in colour management just asking for your opinion?

Best regards
Erik


sRGB, Adobe RGB or ProPhoto RGB each have their place: if you only want to use one color space and mostly print then ProPhoto is clearly a good choice; if you only output to the web then sRGB is the obvious choice because that is currently the only supported color space on the web.  Adobe RGB is not a bad compromise, and it conveniently fits the newer wide-gamut monitors.  If you are printing in black and white it doesn't matter what of the working spaces you use.  And so on ...

Robert
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #448 on: October 03, 2014, 04:28:21 pm »

Hi Robert,

Two questions:

  • Has not both Adobe RGB and sRGB has passed it's best before date, now that we have 4K with Rec. 2020 colour space?
  • Is there a need for a new colour space needed for 8-bit representation of the Rec 2020 colour space?

I don't pretend to be an expert in colour management just asking for your opinion?

Best regards
Erik


Hi Erik,

Well, having just emerged from a long and tedious 'discussion' about color spaces I'm not going to let myself get sucked into another pros-and-cons debate :).  But my opinion, for what it's worth, is that if you are defining a color space for future use, taking into account the likelihood that future devices will be able to display larger gamuts than current ones, then it makes sense to go for a large color space like the Rec 2020 (which also has the advantage of not having negative colors, as does ProPhoto) ... otherwise you will end up getting boxed in as has happened with sRGB.

For an end-user like me, as long as the workspace can comfortably accommodate my image gamut, I don't see any disadvantage in using the older, smaller working spaces (and there are advantages as they present a smaller mapping problem for the profile development engineers).  I equally don't see much disadvantage to using a very large working space like ProPhoto, providing one is careful as it is easy to push the image colors out of (the destination) gamut without realizing it.

As for 8-bit version of the Rec2020 ... well, this probably wouldn't be a good idea because the space is really too large for 8 bits.  You would need to define a smaller gamut, and then it wouldn't be Rec2020 any more, I guess.

What I was really trying to address is the notion presented by Andrew that printing an image after converting it from ProPhoto to sRGB demonstrates that ProPhoto is superior: it doesn't; what it does is to demonstrate that a relative colorimetric mapping of an image that has a wide gamut to a small working space will result in the kind of mess that you can all too easily see, without having to go to print (assuming you have an AdobeRGB-size monitor).

Robert
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bjanes

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Re: Color management myths and misinformation video
« Reply #449 on: October 03, 2014, 04:51:45 pm »

Hi Robert,

Two questions:

  • Has not both Adobe RGB and sRGB has passed it's best before date, now that we have 4K with Rec. 2020 colour space?
  • Is there a need for a new colour space needed for 8-bit representation of the Rec 2020 colour space?

I don't pretend to be an expert in colour management just asking for your opinion?

Best regards
Erik


Erik,

I'm not an expert either, and perhaps Andrew can comment. However, I looked up the Rec 2020 gamut on Wikipedia (shown below, first image). It does not appear to be much wider than Adobe RGB (second image below, which is taken from a paper by Prof Dr Hoffmann). What he describes as real world surface colors are those colors that occur in nature from non-emissve (reflected light) sources. These are outlined by the dashed line. Some of the greens in his diagram appear to be out of the 2020 gamut. Some knowledgeable sources have said that this real world surface color gamut is too restrictive. Personally, I don't see any need for a new color space. Properly used, ProPhotoRGB works fine.

Bill
« Last Edit: October 03, 2014, 04:54:15 pm by bjanes »
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digitaldog

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Re: Color management myths and misinformation video
« Reply #450 on: October 03, 2014, 06:58:50 pm »

sRGB, Adobe RGB or ProPhoto RGB each have their place: if you only want to use one color space and mostly print then ProPhoto is clearly a good choice; if you only output to the web then sRGB is the obvious choice because that is currently the only supported color space on the web. 
And that's why those images are in ProPhoto RGB, they need to be printed and go to the web. The myths and misinformation you missed, because you failed to read the posts here is the suggestion to just use sRGB for everything.
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #451 on: October 04, 2014, 05:21:35 am »

And that's why those images are in ProPhoto RGB, they need to be printed and go to the web. The myths and misinformation you missed, because you failed to read the posts here is the suggestion to just use sRGB for everything.

I've had a quick scan of the thread and I don't see where there is a suggestion (or where there is a myth/misinformation) to use sRGB for everything.  That would be pretty crazy considering the fact that our monitors are now effectively aRGB or wider, and so are our printers, not to mention our cameras.  I don't know if you're referring to Gary Fong or what ... but I'm not going to pay him money to hear his views on the subject: not because I object to paying, but because I'm quite sure I'll learn nothing from it.

A lot of the posts here seem to be about whether or not one color space has more colors than the other etc. I think that's been debated to death and is just a confusion between the number of sample points and the range.

My post had to do with your video, which as far as I can see was the objective of your original post: to get advice from the members here on what should go into your video; and the objective of your video was to debunk some misconceptions.  However your video seems to me to go well beyond that and comes out with a very strong and clear message that ProPhoto is a superior working space to sRGB.  I don't argue that point: it is in some ways because it can encompass a much wider gamut.

What I am querying is your demonstration.  Specifically, I think that you are presenting a misinformation when you convert a wide-gamut image from ProPhoto to sRGB prior to printing, and then say that the resulting print shows the superiority of ProPhoto.  

If you print your test image to a small-gamut paper like a fine art matte paper using a relative colorimetric mapping, you will get the same (or similar) flattening and banding that you get when you convert to sRGB.  The reason is simple: the RC mapping has to shift the very far OOG colors into the small paper gamut and because of the way that RC is defined and implemented, this will result in flat areas, banding, color shifts etc.  If, on the other hand, you use a Perceptual mapping, you may end up with a print that looks more or less OK.  The fact is that we cannot do a perceptual mapping from ProPhoto to sRGB so we cannot do the comparison PP->Small Gamut Print against PP->sRGB->Small Gamut print, with all mapping done perceptually.

On the other hand, what your demonstration SHOULD also have shown, is that your test image contains colors that are massively outside the gamut of currently available monitors and printers: and this is one of the real problems with ProPhoto: that it allows us to produce images that are wildly outside the gamut of our output devices.  That doesn't mean that ProPhoto is bad: it just means that if we use it we should use it with caution ... and we should NEVER convert a ProPhoto image to sRGB without FIRST ensuring that the gamut of the image can be more or less contained within sRGB.

Unfortunately we often do need to convert to sRGB because that is what the web uses: so advice on what to do to get an image with a wide gamut into the small-gamut sRGB space would be a useful contribution.  Could we, for example, construct a table-based sRGB-like profile that would allow us to do a perceptual mapping to this space, followed by a RC mapping to sRGB (thus allowing us to effectively do a perceptual mapping to sRGB)?

Robert
« Last Edit: October 04, 2014, 05:30:36 am by Robert Ardill »
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digitaldog

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Re: Color management myths and misinformation video
« Reply #452 on: October 04, 2014, 11:20:03 am »

I've had a quick scan of the thread and I don't see where there is a suggestion (or where there is a myth/misinformation) to use sRGB for everything.  

I don't know if you're referring to Gary Fong or what ... but I'm not going to pay him money to hear his views on the subject: not because I object to paying, but because I'm quite sure I'll learn nothing from it.

As usual, you're having severe difficulties connecting the dots.

1. The video is called "The benefits of wide gamut working space for print output" and that's exactly what it shows.
2. Yes, this is in a way, a direct response to Gary and no, you don't have to pay to hear his flat earth theories on color management.
3. Yes, there is a big world out there where people like Fong, Crockett, Rockwell and others suggest their audience use sRGB for evertything! The video shows why that's a dumb idea.
4. Any of the actual images in the test page could have been shot and converted in-camera to sRGB. Or shot raw and encoded into sRGB for all further output. The video shows why this is far from an optimal workflow!
5. You're still obsessed and confused about rendering intents, they all clip OOG colors (but do it differently) so I'll ignore your latest post about this here, as should others, as yet another of your rabbit holes and stick to my original idea to put you on the do not call list/ignore. But here I'm replying because you've again failed to understand the points. If you so desire and wish to create your own video addressing these ideas, please do so.
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On the other hand, what your demonstration SHOULD also have shown, is that your test image contains colors that are massively outside the gamut of currently available monitors and printers
I did show that, another video that goes into detail was referenced, the results of that wide gamut data was presented with a file anyone can use to see this. Again, make your own video demonstrating what you think a video on gamut's of working space should show. This thread is many, many pages long, the only one who's come here to suggest the video is flawed is you sir, and the lack of anyone replying to your posts is telling. As such, time to but on the Ardill filter again, you've proven you simply don't get it!
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Unfortunately we often do need to convert to sRGB because that is what the web uses: so advice on what to do to get an image with a wide gamut into the small-gamut sRGB space would be a useful contribution.  Could we, for example, construct a table-based sRGB-like profile that would allow us to do a perceptual mapping to this space, followed by a RC mapping to sRGB (thus allowing us to effectively do a perceptual mapping to sRGB)?
That you still don't understand that going from ProPhoto RGB to sRGB can and can/will clip colors despite any RI used illustrates you're unable to understand a very simple concept of color management and until you do so, going down another Ardill rabbit hole is pointless.
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #453 on: October 04, 2014, 01:27:57 pm »

As usual, you're having severe difficulties connecting the dots.

1. The video is called "The benefits of wide gamut working space for print output" and that's exactly what it shows.
2. Yes, this is in a way, a direct response to Gary and no, you don't have to pay to hear his flat earth theories on color management.
3. Yes, there is a big world out there where people like Fong, Crockett, Rockwell and others suggest their audience use sRGB for evertything! The video shows why that's a dumb idea.
4. Any of the actual images in the test page could have been shot and converted in-camera to sRGB. Or shot raw and encoded into sRGB for all further output. The video shows why this is far from an optimal workflow!
5. You're still obsessed and confused about rendering intents, they all clip OOG colors (but do it differently) so I'll ignore your latest post about this here, as should others, as yet another of your rabbit holes and stick to my original idea to put you on the do not call list/ignore. But here I'm replying because you've again failed to understand the points. If you so desire and wish to create your own video addressing these ideas, please do so. I did show that, another video that goes into detail was referenced, the results of that wide gamut data was presented with a file anyone can use to see this. Again, make your own video demonstrating what you think a video on gamut's of working space should show. This thread is many, many pages long, the only one who's come here to suggest the video is flawed is you sir, and the lack of anyone replying to your posts is telling. As such, time to but on the Ardill filter again, you've proven you simply don't get it! That you still don't understand that going from ProPhoto RGB to sRGB can and can/will clip colors despite any RI used illustrates you're unable to understand a very simple concept of color management and until you do so, going down another Ardill rabbit hole is pointless.


Why do you get so angry if you're right and I'm wrong?

Rendering intents do not all 'clip' colors, unless you include the compression of colors into a smaller space as being 'clipping'.  Of course I understand, as you very well know, that the whole purpose of color management is to attempt to address the misfit between our various input, display and output devices, and that one very important aspect of this is modifying the image colors so that the image can fit into a smaller destination color space in as pleasing (or as accurate) a way as possible.  

Here is a definition of Clip: "To cut, cut off, or cut out with or as if with shears".  Neither the Perceptual nor the Relative Colorimetric mappings do this.  If they did then the colors would simply disappear.  Instead, as you know, the colors are compressed or shifted: in the case of Perceptual the mapping attempts to preserve the relationship between the image's colors; in the case of Relative Colorimetric the mapping brings the out of gamut colors into gamut without attempting to preserve this relationship.  

The effect of these two rendering intents can be very different and the more the image gamut is outside the destination gamut the greater the difference: then one intent may give a much better result than the other.  So having the choice of which intent to use is very important, as the ICC has recognized by defining v4 which DOES allow both perceptual and rendering intents to be used between working spaces (you can download the sRGB v4 icc profile here: http://www.color.org/srgbprofiles.xalter and you will be able to check out, for yourself, the difference between the two rendering intents when applied to a mapping from ProPhoto or Adobe RGB to sRGB).

I do understand that with v2 profiles that the ONLY rendering intent available when going from working space to working space is Relative Colorimetric and that even though the other intents are shown as available in Photoshop they will all use the RC mapping.  This is not necessarily the case with v4 which allows for working space profiles to use tables, so that they can now implement other intents.  Whether they do or not is optional, and, as far as I know, the only color space that currently allows for a Perceptual mapping as well as a Relative Colorimetric mapping is the (Beta) ICC sRGB v4 profile.  But no doubt profile makers will produce versions of ProPhoto and Adobe RGB etc., which will provide both intents.

You certainly go to a lot of trouble in your video to show the benefits of ProPhoto over sRGB, I'll give you that.  But the sense that one gets from the video is that sRGB is inadequate or defective and will in all likelihood yield inferior results compared to ProPhoto.  Well, that may not have been your intent, but that is certainly what comes through to me.  And, as you know, it is NOT true that sRGB will inevitably yield inferior results than ProPhoto.  

Depending on the profile maker, some images may print much BETTER from sRGB, ESPECIALLY if the rendering intent chosen is Perceptual.  Have a look at this really excellent explanation (with animation) if you don't believe me: http://graphics.stanford.edu/courses/cs178/applets/gamutmapping.html.  The rendering intents implemented here are by no means optimal, but they are rigorously correct.

The key is that if the image gamut is contained by both the working space and the destination space then a Relative Colorimetric mapping is the best and safest one to use as the colors will not be changed.  If it is NOT then what we need to do is to check each rendering intent to see which gives the best result: and this will depend on how well the profile implements the mappings.  So a profile from one supplier (say XRite) may give a better result with a Perceptual mapping while one from another supplier (say Argyll) may give a better result with a Relative Colorimetric mapping (or vice versa).

The situation gets even more complicated with v4 as this allows for an optional intermediate gamut called the Perceptual Reference Medium gamut (PRMG) when converting from one color space to another.  This has pros and cons that can (probably will) affect which rendering intent gives the best result.

So do we agree on anything at this stage?  Well yes, I do agree with you that we should absolutely NOT convert a wide-gamut image held in a working space into a smaller-gamut working space unless this is unavoidable.  It is, unfortunately, currently unavoidable for the web: but it is not, by any means, unavoidable for printing.  If we do the conversion before printing then we will be using a RC mapping which WILL bring all of the out of gamut colors into gamut, and in so doing do the kinds of things you demonstrated with your test image.  By converting the image to sRGB we will be damaging the image and so we will get an inferior print. But if the image was already in sRGB, putting it into ProPhoto would not improve the image (and might even result in a slightly worse print).

I also agree that if we want to use only ONE working space then we are better using a big one like ProPhoto. But I see absolutely nothing wrong with using sRGB for images with small gamuts (black and white, needless to say); and Adobe RGB for images with medium-sized gamuts; and ProPhoto RGB for images with large gamuts.  You might say that this is just complicating one's workflow - yes, perhaps it is, but it's nevertheless perfectly valid and will not result in worse prints.

In the example I've given here: http://www.luminous-landscape.com/forum/index.php?topic=93997.0, part of the image colors were outside both sRGB and Adobe RGB and also outside the gamut of a wide-gamut print: in that case, how can I tell what the actual color is?  All I can do is print and hope for the best.  Soft-proofing doesn't help (how could it if the print gamut is wider than my monitor gamut?).  Some of us might prefer to sacrifice some very saturated colors in exchange for being able to view all of the colors on our monitors.  That's a choice ... one which I, for one, am happy with (most of the time, but not, inflexibly, for ALL images).  I am not asking you or anyone else to do the same: that's for each of us to decide.

That others on this forum haven't come out in agreement with me is really irrelevant: this is not an election, it's a matter of fact.  If all of the world agreed (as it once did) that the world is flat, this would not make it so (fortunately :)).

It seems to me that you are doing what Fong et al are doing (I do speak from ignorance as I haven't read/watched these gentlemen's advice, but you tell me they advocate sRGB all the way, so I'll take your word for it) ... but you are doing it at the other end of the spectrum: you're advocating ProPhoto all the way.  Fine, it's your right to do so ... but it is equally my right to disagree with you and to disagree with how you present your argument.

But it would certainly be very good if we could agree to disagree ... without the personal attacks.

Robert
« Last Edit: October 04, 2014, 01:36:25 pm by Robert Ardill »
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smthopr

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Re: Color management myths and misinformation video
« Reply #454 on: October 04, 2014, 03:36:03 pm »

Guys, correct me if I'm mistaken, but... Doesn't a conversion from prophotoRGB to sRGB map all colors to reproduce the same except for out of gamut colors which will convert to the nearest color?

Which implies that, for example, all very saturated, out if gamut pure reds will convert to the same maximum value in sRGB. IOW they clip when using RC intent.

To avoid any clipping one would do an "assign profile" command and then see desaturated color.

I think the lesson of all these pages here is that we need displays that can reproduce the gamut of all the other output devices!
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #455 on: October 04, 2014, 04:17:43 pm »

Guys, correct me if I'm mistaken, but... Doesn't a conversion from prophotoRGB to sRGB map all colors to reproduce the same except for out of gamut colors which will convert to the nearest color?

Which implies that, for example, all very saturated, out if gamut pure reds will convert to the same maximum value in sRGB. IOW they clip when using RC intent.

Yes, with v2 profiles a pure red 255,0,0 in ProPhoto will map to a pure red 255,0,0 in sRGB and as Andrew explained these are not the same colors.  So the color is shifted, but not clipped (unless you define this shifting as a clipping).

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To avoid any clipping one would do an "assign profile" command and then see desaturated color.

I think the lesson of all these pages here is that we need displays that can reproduce the gamut of all the other output devices!


Well, Assign Profile is doing a completely invalid interpretation of the data - the only time it makes sense to use is when there is no profile attached to the image, and then we make a best guess as to what color space it should have (usually sRGB).

It would certainly make things a whole lot easier if our displays were the widest gamut devices in our armory!!

Robert
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Eyeball

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Re: Color management myths and misinformation video
« Reply #456 on: October 04, 2014, 05:06:04 pm »

Yes, with v2 profiles a pure red 255,0,0 in ProPhoto will map to a pure red 255,0,0 in sRGB and as Andrew explained these are not the same colors.  So the color is shifted, but not clipped (unless you define this shifting as a clipping).

Robert, I think most people would consider this case to be "clipping", rather than "shifting", for a few reasons:

- It is the color value of the pixel that is being truncated or "clipped" to the border of the smaller gamut.  The pixel itself is not being clipped or eliminated.

- The important difference between pixels with "clipped" color values when using relative colorimetric and pixels with "shifted" color values when using perceptual is that the shifted values could be reverse-shifted back to the original gamut (or at least something close).  Clipped values cannot be "reverse-clipped" because that relative gamut-positioning information has been lost.  In your example, there are a whole range of potential color values that are going to get clipped to 255,0,0 in sRGB and once they are clipped that way, there is no way to re-create that original range of out-of-gamut color values.

- A similar thing occurs when we commonly refer to "clipped" highlights or shadows.  It doesn't mean that the pixel turns invisible or is eliminated from the image.  It means that the true brightness value was beyond what could be recorded and was therefor recorded as the min or max value.  The true brightness was "clipped" to the min or max pixel value.  Information was lost that cannot be recovered.
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #457 on: October 04, 2014, 05:12:24 pm »

Robert, I think most people would consider this case to be "clipping", rather than "shifting", for a few reasons:

- It is the color value of the pixel that is being truncated or "clipped" to the border of the smaller gamut.  The pixel itself is not being clipped or eliminated.

- The important difference between pixels with "clipped" color values when using relative colorimetric and pixels with "shifted" color values when using perceptual is that the shifted values could be reverse-shifted back to the original gamut (or at least something close).  Clipped values cannot be "reverse-clipped" because that relative gamut-positioning information has been lost.  In your example, there are a whole range of potential color values that are going to get clipped to 255,0,0 in sRGB and once they are clipped that way, there is no way to re-create that original range of out-of-gamut color values.

- A similar thing occurs when we commonly refer to "clipped" highlights or shadows.  It doesn't mean that the pixel turns invisible or is eliminated from the image.  It means that the true brightness value was beyond what could be recorded and was therefor recorded as the min or max value.  The true brightness was "clipped" to the min or max pixel value.  Information was lost that cannot be recovered.

Yes, you're quite right ... I was being pedantic :).

Robert
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smthopr

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Re: Color management myths and misinformation video
« Reply #458 on: October 04, 2014, 06:03:15 pm »

Yes, with v2 profiles a pure red 255,0,0 in ProPhoto will map to a pure red 255,0,0 in sRGB and as Andrew explained these are not the same colors.  So the color is shifted, but not clipped (unless you define this shifting as a clipping).

Well, Assign Profile is doing a completely invalid interpretation of the data - the only time it makes sense to use is when there is no profile attached to the image, and then we make a best guess as to what color space it should have (usually sRGB).

It would certainly make things a whole lot easier if our displays were the widest gamut devices in our armory!!

Robert

If ppRGB 255,0,0 and 250,0,0 and 245,0,0 all map to sRGB 255,0,0 then I would refer to that as clipping.
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Robert Ardill

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Re: Color management myths and misinformation video
« Reply #459 on: October 04, 2014, 06:22:07 pm »

If ppRGB 255,0,0 and 250,0,0 and 245,0,0 all map to sRGB 255,0,0 then I would refer to that as clipping.

If you look at my previous post you will see that I am not arguing about the term clipping.  As I said, I was being a bit picky. 

Robert
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