Luminous Landscape Forum
Site & Board Matters => Article Discussions => Topic started by: inspiration.in.print on March 27, 2020, 07:10:12 pm
-
For anybody reproducing artwork this must be the most interesting article for along time. Just leaving more me with more questions?
How we use it to create a camera profile?
A Spanish web sit that dose not support English?
How it work with X-Right Software?
The Super Chroma Prophoto.tif is the best calibration that I have seen but can it get even better?
Anticipating a follow up to this article
-
What raw converter are you using? If from Adobe (LR/ACR) this simply isn't going to fly; never use (nor need) ICC camera profiles.
-
What are the spectral characteristics of the patches in the chart? They aren't created with process colors, are they? What is the stability of the spectra?
Jim
-
For anybody reproducing artwork this must be the most interesting article for along time. Just leaving more me with more questions?
How we use it to create a camera profile?
A Spanish web sit that dose not support English?
How it work with X-Right Software?
The Super Chroma Prophoto.tif is the best calibration that I have seen but can it get even better?
Anticipating a follow up to this article
Thanks!
- The process is done by capturing the chart like if it were a reproduction and then create the profile using a special software, in a few words.
- X-Rite software cannot create profiles for it as by now.
- Yes, with BasICColor Input 6 you can obtain actually even beter profiles.
Regards,
-
What are the spectral characteristics of the patches in the chart? They aren't created with process colors, are they? What is the stability of the spectra?
Jim
The chart is printed with Epson Ultrachrome inks.
Regarding the spectral characteristics, though there are not present the exact same colors as -say- the ones in the Colorchecker in the Superchroma, there are some patches that are very similar both in color and spectral curve. I can send you graphs in you wish.
Regards,
-
The chart is printed with Epson Ultrachrome inks.
Regarding the spectral characteristics, though there are not present the exact same colors as -say- the ones in the Colorchecker in the Superchroma, there are some patches that are very similar both in color and spectral curve. I can send you graphs in you wish.
Regards,
So they are process colors. That's an issue, since the basis functions for all the spectra will be derived from the number of inks used in the printer.
Jim
-
So they are process colors. That's an issue, since the basis functions for all the spectra will be derived from the number of inks used in the printer.
Jim
Indeed and more here:
https://luminous-landscape.com/hr-1-superchroma/
1. To offer the largest gamut available today, thanks to giclée printing with 12 pigmented inks.
As soon as I got to giclée, I was done. ;)
-
Indeed and more here:As soon as I got to giclée, I was done. ;)
Yup. French slang for ejaculation, right?
-
Yup. French slang for ejaculation, right?
Oui 😱💦
-
Indeed and more here:As soon as I got to giclée, I was done. ;)
FYI: https://en.wikipedia.org/wiki/Gicl%C3%A9e
-
So they are process colors. That's an issue, since the basis functions for all the spectra will be derived from the number of inks used in the printer.
Well, my tests and measurements (and clients) don't prove that's an issue as you can see in the article.
Regards,
-
Well, my tests and measurements (and clients) don't prove that's an issue as you can see in the article.
Regards,
If it makes you happy, that's great. And it's certainly the easy way to go. But it's an invitation to metametric color errors (both lighting and subject induced), unless you're mostly taking pictures of printer output.
Jim
-
FYI: https://en.wikipedia.org/wiki/Gicl%C3%A9e
"If fifty million people say a foolish thing, it is still a foolish thing."
-Bertrand Russell
This a massively made up BS term from long ago that the fellows who actually came up with the use for fine art printing has always dismissed (Nash and Holbert).
https://www.merriam-webster.com/dictionary/giclée
NOTE: According to paper and online sources, the French word giclée was first applied to ink-jet prints in 1991 by Jack Duganne, a printmaker working for Nash Editions in Manhattan Beach, California. A relatively early account of the origin can be found in “Paper Trail,” the editorial column of On Paper: The Journal of Prints, Drawing and Photography, vol. 1, no. 5 (May-June, 1997), p. 5: “When, in the mid-1980’s [recte, 1990-91], Nash Editions became the first press extensively involved in computer printmaking (with an Iris printer, in this case), it dubbed the works digital ink jet prints. This reflected, in a matter-of-fact manner, the process that takes an image scanned or generated on a computer, and then sends that image to be printed on a machine that spits out ink in minuscule jets … . ‘We had a man named Jack Duganne working with us at the time, who recognized there was no way to talk about this,’ says Nash Editions’s Mac Holbert. ‘He felt that if we just called it “digital ink jet print,” it would have absolutely no impact on the art world. So he went home to his French dictionary and found the word “gicler,” which means “to spray” or “to jet.”’ (Later, the printers discovered that the term in French was slang for ‘to ejaculate,’ which pleased them even more.) The term ‘giclée’ is still occasionally used. But even Nash Editions abandoned it as a ‘euphemism,’ and the more cumbersome ‘digital ink jet print’ prevails.”
-
If it makes you happy, that's great.
Or as the late, great expert on color (Bruce Fraser) would say:
"If you're happy with what you have, be happy that you're happy with what you have!"
Doesn't change the colorimetric facts you've pointed out:
an invitation to metametric color errors (both lighting and subject induced), unless you're mostly taking pictures of printer output.
-
If it makes you happy, that's great. And it's certainly the easy way to go. But it's an invitation to metametric color errors (both lighting and subject induced), unless you're mostly taking pictures of printer output.
Jim
Jim, it's not a question that I'm happy or not. If you watch the results with the colorchecker you can see both results, with it's own (colorchecker) profile and the SuperChroma profile, and judge yourself. It's just data.
Apart from that, as I explained and stated several times: this chart is meant to be used in professional environments where low quality and/or CRI lights will be used, so there's very few metameric issue to be seen.
I don't believe any serious professional photographer or museum will use cheap chinese lights for their work. And with high quality lights (Profoto, Broncolor...) the spectral curve is really smooth.
Regards,
-
Apart from that, as I explained and stated several times: this chart is meant to be used in professional environments where low quality and/or CRI lights will be used, so there's very few metameric issue to be seen.
First off, isn't that bas-ackwards? In professional environments, it is more likely that the lights will be of high quality, not less likely.
And second, metameric issues are not confined to situation where the spectra of the illuminant is smooth. Look at what happens to a print when illuminated by various black-body illuminants.
And third, it's possible to have high-CRI lights that are peaky.
Jim
-
First off, isn't that bas-ackwards? In professional environments, it is more likely that the lights will be of high quality, not less likely.
And second, metameric issues are not confined to situation where the spectra of the illuminant is smooth. Look at what happens to a print when illuminated by various black-body illuminants.
And third, it's possible to have high-CRI lights that are peaky.
Jim
And that's just data :D
-
First off, isn't that bas-ackwards? In professional environments, it is more likely that the lights will be of high quality, not less likely.
And second, metameric issues are not confined to situation where the spectra of the illuminant is smooth. Look at what happens to a print when illuminated by various black-body illuminants.
And third, it's possible to have high-CRI lights that are peaky.
Jim
Sorry, a mispelling. I meant high quality lights.
-
The image that comes to my mind is that of two seagulls who just flew over a guy and crapped on his head. Then flew off to eat sardines on a pylon.
So, Kasson et al, if you have something constructive to say - like what kind of ink you require in your aviary, or which color reference is the best on the market - please do so.
Hugo, what is your preferred hardware & software workflow to utilize your card?
thanks --
Brandt
-
The image that comes to my mind is that of two seagulls who just flew over a guy and crapped on his head. Then flew off to eat sardines on a pylon.
So, Kasson et al, if you have something constructive to say - like what kind of ink you require in your aviary, or which color reference is the best on the market - please do so.
It sounds like neither you nor the OP are appreciating the thrust of my argument as to why you need more independent spectra in your test target, not more colors that are the result of a narrow set of basis functions.
I've prepared a detailed explanation:
https://blog.kasson.com/the-last-word/two-digital-camera-color-fallacies/
Jim
-
hi Jim,
Thanks for the post on your site, that is constructive and does help explain the problem. That said, what you don't address is what's the best we *do* currently do (practically speaking) -- not to be confused with what the best we *can* currently do might be.
I.e. out in the messy real world of taking pictures and printing them and trying to get 'what I saw' to 'what I want' to 'what I see on my screen/print', is there a workflow, including a calibration target, that addresses the metameric issues you describe as well as the too-few-sample patches issue (from your post, it sounds like solving this would require calibration targets comprising actual human skin, which is probably not where we want to go...)? If yes, what is it? If no, what is in your opinion the best solution that is commercially relevant and realistically implementable by an enthusiast photographer (rather than, say, a major Hollywood studio, etc.)?
regards,
Brandt
-
Put another way, there are the following possibilities and ensuing questions:
1 - the problem is insoluble.
Q: what's the best practical solution that we have now, and are there any obvious ways to improve upon it
2 - the problem is soluble, but has not been solved.
Q: Again, what's the best practical solution currently available, and what would be required to improve this solution to the point that it meets the challenge
3 - the problem is soluble, and has been solved
Q: Is this solution commercially available, and if so, practical for individuals to implement.
-
Put another way, there are the following possibilities and ensuing questions:
1 - the problem is insoluble.
Q: what's the best practical solution that we have now, and are there any obvious ways to improve upon it
2 - the problem is soluble, but has not been solved.
Q: Again, what's the best practical solution currently available, and what would be required to improve this solution to the point that it meets the challenge
3 - the problem is soluble, and has been solved
Q: Is this solution commercially available, and if so, practical for individuals to implement.
As long as cameras don't meet the Luther-Ives condition, the problem is not perfectly solvable. However, we can come pretty close, for limited lighting spectra and limited subject matter. For those, the problem is close to solvable, given a camera with a tractable set of color filter array dyes and an appropriate lighting source. A demonstration of this is the success of heritage preservation photographers in color reproduction. The key to successfully doing this is using patches of the materials to be photographed, illuminated by light that is the same as will be used for the actual photography. Gather the patches, measure them with a spectrophotometer, photograph them, input the spectra to the profile making software along with the raw file.
The problem can also be nearly solved, and more accurately, by using a monochrome sensor and a filter wheel consisting of more than three segments. But there is no nonspecialist commercial software to deal with such a camera. As the number of segments in the filter wheel increases, the accuracy of the solution improves.
But most photographers don't want accurate color. Hunt defines possible objectives for color reproduction:
Spectral color reproduction, in which the reproduction, on a pixel-by-pixel basis, contains the same spectral power distributions or reflectance spectra as the original.
Exact color reproduction, in which the reproduction has the same chromaticities and luminances as those of the original.
Colorimetric color reproduction, in which the reproduced image has the same chromaticities as the original, and luminances proportional to those of the original.
Equivalent color reproduction, in which the image values are corrected so that the image appears the same as the original, even though the reproduction is viewed in different conditions than was the original.
Corresponding color reproduction, in which the constraints of equivalent color reproduction are relaxed to allow differing absolute illumination levels between the original and the reproduction; the criterion becomes that the reproduction looks the same as the original would have had it been illuminated at the absolute level at which the reproduction is viewed.
Preferred color reproduction, in which reproduced colors differ from the original colors in order to give a more pleasing result.
Most photographers want the last. That gives a lot of wiggle room, although it introduces an element of subjectivity. All the commercial raw developers are set up to attempt to deliver the last by default, and there are huge controversies about how well they do that, with hotly-debated opinions on all sides.
I see this is getting long. To be continued.
Jim
-
3 - the problem is soluble, and has been solved
Q: Is this solution commercially available, and if so, practical for individuals to implement.
If you're not too picky about accuracy, the problem has been solved, in various ways. In my opinion, the most accurate way to generate a color profile for a camera is to measure the spectral responses of the raw channels, and compute the profile from there. However, that way requires equipment that most photographers don't have, and, more to the point, don't know how to use. There are two main ways to do that. One is to photograph -- with no lens on the camera -- the image cast by a grating or a prism. Now we have the spectral response of each channel, but we don't know the amount of energy at each wavelength. To get that we need to measure the output of the rainbow-generating device vs wavelength. Put those to together and we have the spectral response of the channels. There are endless variations on this theme. You can also buy a device that has many individually-filtered spectrally disparate light sources, and that's the other method. I believe, but am not sure, that Adobe and others generate their profiles by looking at the spectral response of the cameras.
Whether doing the above is practical for individuals to implement is highly dependent on the individual. I would say that most people don't have the time, technical ability, mathematical and programming skills, and, most importantly, interest, to do that kind of work. Remember, most people don't want accurate color anyway.
Many people are entirely satisfied by photographing commercial patch sets. However, for best results, you should measure your patch set with a spectrophotometer, since there is variation in the patches and they change with age. The X-rite SG patch set delivers more accurate results than the CC24, in my experience. With some color profile making software, you can add your own patches, measured with your own spectrophotometer.
If your camera obeyed the Luther-Ives condition, you could use patches that covered the range of colors that you're interested in. Since it does not, you must use patches that cover the range of spectra that you're interested in.
Most people are satisfied with commercial profiles, once they find one they like. Many who are not find that they can edit those profiles to their satisfaction. Adobe provides tools to do that.
Here is some background reading:
https://blog.kasson.com/the-last-word/the-color-reproduction-problem/
https://en.wikipedia.org/wiki/Tristimulus_colorimeter
https://blog.kasson.com/nikon-z6-7/camera-differences-in-color-profile-making/
Jim
-
I don't believe any serious professional photographer or museum will use cheap chinese lights for their work.
right, right - their for exampe will use chinese LEDs from the likes of Yuji ;D which will be put in nice boxes by the likes of https://dtculturalheritage.com/dt-photon-custom-cultural-heritage-lighting/
-
. And with high quality lights (Profoto, Broncolor...) the spectral curve is really smooth.
and if you refer to strobes you imagine that they have some special xenon bulbs ;D - what they can boast sometimes is more stable spectrum vs power output range, but then you can use way cheaper PCB Einstein
-
hi Jim,
These two posts, plus the one on your blog from this week, are a very helpful crash course on this problem. Thank you.
I am a hobbyist photographer, and qua hobbyist I'm a little more interested in 'what I want' rather than 'what my eyes really saw', though I prefer to stay relatively closely tethered to 'what I saw.' I'm not a follower of the Renoir/Kincade/Peter Lik school.
Meanwhile, after 10 years of development, I'm close to launching a very high-end consumer product that will be painted in colors of the customer's choice. This product will be sold online. Ultimately samples of the actual paint on the actual substrate will have to be sent to customers for approval. However it would save a lot of time and aggravation if the colors I see on my monitors match as closely as possible the automotive paints used. Carrying this accuracy through to customer viewing devices and print collateral would also be very helpful. I realize that I can't make customers profile their smartphones, but I want to control what I can. Qua product vendor, I care about accuracy a great deal.
From what you've said, it sounds like the practical answer from your perspective is an X-rite setup using their SG target. (?) One minor question, do you know what technology they use to print their target? They provide basically zero technical information on their site about the product.
regards,
Brandt
-
From what you've said, it sounds like the practical answer from your perspective is an X-rite setup using their SG target. (?) One minor question, do you know what technology they use to print their target? They provide basically zero technical information on their site about the product.
I'll get to the practical answer in another post, but I can deal with this on fairly simply. The patches in the X-Rite targets consist of paints that were mixed to have the desired spectrum. The spectra that they chose consist of what they consider to be commonly-photographed objects.
If you know anything about offset printing, they are spot colors, not process colors.
I don't know for sure, but I imagine that they spray paint substrates, then cut those up into the patches, and then glue the patches to the backing board of the target.
Jim
-
Meanwhile, after 10 years of development, I'm close to launching a very high-end consumer product that will be painted in colors of the customer's choice. This product will be sold online. Ultimately samples of the actual paint on the actual substrate will have to be sent to customers for approval. However it would save a lot of time and aggravation if the colors I see on my monitors match as closely as possible the automotive paints used. Carrying this accuracy through to customer viewing devices and print collateral would also be very helpful. I realize that I can't make customers profile their smartphones, but I want to control what I can. Qua product vendor, I care about accuracy a great deal.
From what you've said, it sounds like the practical answer from your perspective is an X-rite setup using their SG target.
I'd use some actual paint samples for the targets. Have you looked at the paint sample spectra to see how well-behaved they are?
Jim
-
Meanwhile, after 10 years of development, I'm close to launching a very high-end consumer product that will be painted in colors of the customer's choice. This product will be sold online. Ultimately samples of the actual paint on the actual substrate will have to be sent to customers for approval. However it would save a lot of time and aggravation if the colors I see on my monitors match as closely as possible the automotive paints used. Carrying this accuracy through to customer viewing devices and print collateral would also be very helpful. I realize that I can't make customers profile their smartphones, but I want to control what I can. Qua product vendor, I care about accuracy a great deal.
If you want to put colorimetrically correct patches on your web site, you don't need a camera at all. Just measure the paint chips with a spectrophotometer, calculate the colorimetric values in sRGB when they are lit by D65 light, and use those values for your posted color patches.
Jim
-
From what you've said, it sounds like the practical answer from your perspective is an X-rite setup using their SG target.
if you want to create profiles using targets - get a decent spectrophotometer, decent light (to go above high 2K or very low 3K spectrum you need to get a strobe or if you want a constant light then Solux / https://www.solux.net/cgi-bin/tlistore/index.html / or for example Yuji sells some ready LED solutions if you can't DIY = https://store.yujiintl.com/collections/high-cri-led-lights ), rawdigger & free dcamprof ( https://torger.se/anders/dcamprof.html ) and you can use "synthetic targets" buy shooting shooting various materials separately and combining the data (also read _completely_ the megathread @ https://forum.luminous-landscape.com/index.php?topic=100015.0 )
-
I'd use some actual paint samples for the targets.
enterprising person who is capable of DIY work can hit a proper supply shop and buy actual pigments to make his own paints to paint patches for targets
-
If you want to put colorimetrically correct patches on your web site, you don't need a camera at all. Just measure the paint chips with a spectrophotometer, calculate the colorimetric values in sRGB when they are lit by D65 light, and use those values for your posted color patches.
indeed - I'd just suggest to Sea-Speak to get software like BabelColor Patchtool to automate the work with that to some extent (it is not that expensive product)
-
enterprising person who is capable of DIY work can hit a proper supply shop and buy actual pigments to make his own paints to paint patches for targets
Sounds like the poster already has access to samples: " Ultimately samples of the actual paint on the actual substrate will have to be sent to customers for approval. "
-
Sounds like the poster already has access to samples: " Ultimately samples of the actual paint on the actual substrate will have to be sent to customers for approval. "
indeed, as you noted above he does not need to photograph anything... unless he wants to photograph the ready product as a whole
-
hi,
Now we're cooking with gas. A few items.
-I'm a hobby letterpress printer. Totally get the spot vs process distinction.
-I haven't looked at actual paint samples yet, nor measured, to see how well-behaved their spectra are.
-I can definitely get some test panels painted and measured with a spectrophotometer. I'm a few months away from that point but will get there.
-Babelcolor patchtool is reasonably priced, no problem to get that software.
Questions
-Re lights - I put Soraa Vivid lamps in my house. Wondering whether you have looked at these and whether they would be suitable. I suppose I need to figure out whether Soraa lamps can be used to construct a D65 source.
-Re spectrophotometers, are the Xrite products the best practical product available, or is there a different vendor with a better mousetrap?
-
-I'm a hobby letterpress printer. Totally get the spot vs process distinction.
-I haven't looked at actual paint samples yet, nor measured, to see how well-behaved their spectra are.
-I can definitely get some test panels painted and measured with a spectrophotometer. I'm a few months away from that point but will get there.
-Babelcolor patchtool is reasonably priced, no problem to get that software.
Questions
-Re lights - I put Soraa Vivid lamps in my house. Wondering whether you have looked at these and whether they would be suitable. I suppose I need to figure out whether Soraa lamps can be used to construct a D65 source.
-Re spectrophotometers, are the Xrite products the best practical product available, or is there a different vendor with a better mousetrap?
I use the X-Rite spectros, and have for about 30 years, although the manufacturer names have changed. I am currently using two i1Pros and an iSis. The newest i1Pro, the 3, doesn't have a lot of software support yet, though.
For illumination of the samples, ideally I'd use the same lighting I expect the user to use to evaluate the product. You don't need a D65 source to calculate the spectrum of the sample illuminated by a D65 light. Take the reflectivity spectrum of the sample and perform a wavelength-by-wavelength multiplication by the spectrum of D65.
It's less accurate, but you can use the Bradford adaptation algorithm to change white points, too.
I don't know how you're going to control the adaptation of the viewer when she is looking at the samples on the web, but adaptation can make a huge difference in color appearance.
Jim
-
-Re lights - I put Soraa Vivid lamps in my house. Wondering whether you have looked at these and whether they would be suitable. I suppose I need to figure out whether Soraa lamps can be used to construct a D65 source.
If you're going to be taking photographs, I'd recommend a Xenon flash tube from a brand name vendor. And I'd go out on a limb and put Godox into that category.
The Soraa lamps I've seen have a big peak in the blue part of the spectrum.
https://blog.kasson.com/the-last-word/further-adventures-in-observer-metameric-failure/
Jim
-
Indeed, the Soraa LED I measured wasn't anything to write home about and not close to as ideal as the Solux.
-
ok, good to know the Soraa lights can be ruled out. Any experience with Waveform? They have a claimed 99CRI D65 LED strip source that I could use to build a lamp.
https://store.waveformlighting.com/collections/led-linear-modules/products/absolute-series-99-cri-led-linear-module?variant=8190565777510
Thanks for the pointer to Solux, and to Godox for bulbs. I will need to take some photos of actual products at some point - won't only be able to use the spectrophotometer directly on paint sample panels. That said - for sample panels - if I were to buy an off the shelf solution rather than build a box, is Just Normlicht clearly better/worse than Pantone?
-
ok, good to know the Soraa lights can be ruled out. Any experience with Waveform? They have a claimed 99CRI D65 LED strip source that I could use to build a lamp.
https://store.waveformlighting.com/collections/led-linear-modules/products/absolute-series-99-cri-led-linear-module?variant=8190565777510
Thanks for the pointer to Solux, and to Godox for bulbs. I will need to take some photos of actual products at some point - won't only be able to use the spectrophotometer directly on paint sample panels. That said - for sample panels - if I were to buy an off the shelf solution rather than build a box, is Just Normlicht clearly better/worse than Pantone?
The Godox are strobes, not bulbs. I'd use those instead of LEDs, and I'd use standard light modifiers. I wouldn't put too much credence in CRI for this kind of work; it's only using 18 patches of the CC24.
Why won't you be able to use a spectro directly on the sample panels?
As to the sample images, you could just use a Lumariver Repro profile, and edit the pictures so that the painted parts fell into the range indicated by your spectro measurements.
Jim
-
ok, good to know the Soraa lights can be ruled out. Any experience with Waveform? They have a claimed 99CRI D65 LED strip source that I could use to build a lamp.
https://store.waveformlighting.com/collections/led-linear-modules/products/absolute-series-99-cri-led-linear-module?variant=8190565777510
These still have spikes in the blue part of the spectrum.
-
Got it. Understood that the Godox are strobes. I typed 'bulb' when I should have typed 'flash tube'. I meant that I understood you to be telling me that the Godox flash tubes are reasonably good.
And, sorry, I got myself a little confused there - thought I would need to have a D65 light source separate from the spectrophotometer for characterizing paint samples, but of course the spectrophotometer has that source built into it. (And, having spent enough time on the Solux website I now see that they offer the Colorview 6500K light booth, which should be adequate should I need to use my camera to photograph paint samples; I can imagine scenarios in which that becomes useful)
So putting this all together:
1 - making web rendering colors as accurate as possible (I am using Keyshot for CAD rendering, will have Keyshot interactives on the website, and will have to figure out how to set the sRGB values in that software for a given color):
-Produce paint samples with the actual paint on the actual substrate
-Measure physical samples w i1 spectrophotometer and convert to sRGB coordinates for web display purposes
-Use Babelcolor patch tool to manage the sample collection and conversion process
-Calibrate monitor with the same spectrophotometer, and suggest less expensive version (e.g. i1 Display Pro) to customers if they are interested in picking a custom color (to make the narrowing-down process more efficient).
2 - When making photos of finished product:
-Use good quality strobes (e.g. Godox). Sounds like if I can generate the environmental illumination with Solux bulbs that would be ideal.
-Use ColorChecker SG target (or other wide-gamut target that uses spot rather than process colors).
-Monitor calibration, etc. as above.
Have I correctly understood the basic workflow elements?
-
As for CRI, it's a bit of a kludge to make a light source appear to be closer to daylight for marketing and light manufacturers. CRI was developed in large part to aid in the sales of Fluorescent tubes. There are BCRA tiles used to compare under a reference light source but only eight. That's too small a set of tiles. That make it easy to create a spectrum that will render the 8-14 tiles and doesn't tell us that the light source is full spectrum. It doesn't tell us how the other colors will render. My understanding is there are two reference sources; Tungsten for warm bulbs and D50 for cool ones: Above and below 4000K. That means that a normal tungsten bulb and perfect daylight both have a CRI of 100! As such, a high CRI is a decent gauge of how well a light will preform in your home but not such a great indicator of how well it will work for photography and proofing. Both a Solux 48 and a "full spectrum" tube from home depot may have a CRI of 97. I can assure you the Home Depot bulb has a giant mercury spike and some spectral dead spots.
A better metric is called CQS (15 very colorful patches). That doesn't tell us about the spectrum which is even a better way to evaluate the illuminant.
-
Hugo, what is your preferred hardware & software workflow to utilize your card?
thanks --
Brandt
Regarding to hardware, well, that's up to your taste and budget. Almost any decent camera these days with a good lens cap be up to the task. However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.
In terms of profiling software, I've found that the best are BasICColor Input and Profilemaker 5 (yes, still the old one) followed (by a noticeable margin) by Lumariver and all Argyll-based software.
For RAW developing: CaptureOne without any doubt.
PS: Thanks for the empathy.
-
However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.
And yet, neither has a color gamut. Cameras don't have color gamuts. An arbitrary colorimetric camera profile may have a color gamut but the camera doesn't.
http://www.color-image.com/2012/08/a-digital-camera-does-not-have-a-color-gamut/
-
Regarding to hardware, well, that's up to your taste and budget. Almost any decent camera these days with a good lens cap be up to the task. However, regarding to color gamut of the sensor, Canon and Sony not high res are some of the best.
I've found that a good lens cap makes capturing good colors difficult. A lousy lens cap works better. Or even no cap at all.
I'm with Andrew on the gamut of sensors, except in special cases not found in real cameras.
Jim
-
Sensors have a color gamut because its limited by the very filters of the CFA.
-
Sensors have a color gamut because its limited by the very filters of the CFA.
Sorry, completely wrong. Ask some actual color scientist!
I did! I asked it to Mark D. Fairchild from RIT and I just would like to share his answer here:
"This one is easy for me … cameras absolutely do not have gamuts
A color gamut is the range of colors produced by a device or system. I can take an image from any camera and produce any colors I like.
So I fall strongly, and unequivocally, on the side that says cameras do not have color gamuts. (FWIW, this isn’t even a discussion among the faculty in our program, we all agree on this.)
The human eye also does not have a gamut. The spectral locus on chromaticity diagram (which is also missing a dimension) simply shows the response of the eye to monochromatic light. The limit is in the light, not the eye. The camera can also respond to all that light."
-
The chart is printed with Epson Ultrachrome inks.
Regarding the spectral characteristics, though there are not present the exact same colors as -say- the ones in the Colorchecker in the Superchroma, there are some patches that are very similar both in color and spectral curve. I can send you graphs in you wish.
Regards,
Hi,
I am not sure inkjet prints are very good for calibration targets. The reason that the colors are just a mix of inkjet inks that are intended to yield a metameric match for the the colors printed under a set of viewing conditions.
My guess would be that if you look at say a reflectance spectrum from say 'human skin' and compare with reflectance spectrum from a printed patch, they could have very different spectral response, they could still yield Lab values that are pretty.
So, I would avoid printed targets, but use some well established test chart, like the ColorChecker variants from XRite.
Best regards
Erik
-
I am not sure inkjet prints are very good for calibration targets.
Neither is Jim or I. But the one fellow who is sure digital cameras have a color gamut (despite the text from no less than three color scientists who say they do not) is sure it's an OK process. But then there's a sales incentive here no? :o
-
Neither is Jim or I. But the one fellow who is sure digital cameras have a color gamut (despite the text from no less than three color scientists who say they do not) is sure it's an OK process. But then there's a sales incentive here no? :o
Not a gamut:
(https://torger.se/anders/img/ssf_csep.png)
'This diagram in u’v’ chromaticity coordinates shows the color separation capability of a Canon EOS 5D Mark II.'
Black areas essentially indicate areas where the sensor is 'color blind', that is cannot separate between colors. The irregular shape is "Pointer's gamut" that includes all known non specular colors in nature.
Source: https://torger.se/anders/dcamprof.html
Best regards
Erik
-
From the FAQ's on Munsell Color Science Laboratory:
Question:
"Digital image sensors (such as those used in digital cameras) use red, green, blue ink-based color filters to generate color. Do they therefore have a color gamut that limits the range of colors that they can detect? (255)"
Answer:
"Let's start with the short answer to your question; there is no such thing as a camera, or scanner, gamut. A gamut is defined as the range of colors that a given imaging device can display. To say that a camera had a gamut would be to imply that you could put a color in front of it that it could not possibly respond to. While it is certainly possible that two colors that are visually distinct might be mapped into the same color signals by a camera, that does not mean that the camera could not detect those colors. It just couldn't discriminate them. For example, a monochrome sensor will map all colors into a grayscale image and encode it as such. Certainly the encoding has a gamut (in this case a lightness range with no chroma information), but did the camera responded to all the colors put before it. It is the encoding that imposed the gamut. In the color world, encoding is based on some explicit or implied display. For example, sRGB is a description of a display and therefore defines a gamut (but only if the sRGB values are limited in range). If a camera encodes an image in sRGB, that doesn't mean that the range of colors the camera detected are only from within the sRGB display gamut, but it means the camera data have been transformed to best use that sRGB encoding. As long as a camera has three or more sensors that span the visual spectrum, then it will respond all the same stimuli as our visual system. Whether the camera can discriminate colors as well as the human visual system will depend on the encoding of the camera signals, quantitization, and the details of the camera responsivities. (To return to the black and white system, that camera encodes all the colors into a gray scale. They could then be displayed as any color within a given display, but many colors from the original scene would be mapped to the same values.)
Since there is no such thing as a gamut for an input device, then there is no way to compute it or calculate a figure of merit. Generally, the accuracy of color capture devices is assessed through the accuracy of the output values for known inputs in terms of color differences. Also, sensors are sometimes evaluate in terms of their ability to mimic human visual responses (and therefore be accurate) using quantities with names like colorimetric quality factor, that measure how close the camera responsivities are to linear transformations of the human color matching functions. Doing an internet search on "colorimetric quality factor" will lead you in the right direction."
https://www.rit.edu/cos/colorscience/rc_faq_all.php#255
I'll post this again too:
Digital cameras don't have a gamut, but rather a color mixing function. Basically, a color mixing function is a mathematical representation of a measured color as a function of the three standard monochromatic RGB primaries needed to duplicate a monochromatic observed color at its measured wavelength. Cameras don’t have primaries, they have spectral sensitivities, and the difference is important because a camera can capture all sorts of different primaries. Two different primaries may be captured as the same values by a camera, and the same primary may be captured as two different values by a camera (if the spectral power distributions of the primaries are different). A camera has colors it can capture and encode as unique values compared to others, that are imaginary (not visible) to us. There are colors we can see, but the camera can't capture that are imaginary to it. Most of the colors the camera can "see" we can see as well. Yet some cameras can “see colors“ outside the spectral locus however every attempt is usually made to filter those out. Most important is the fact that cameras “see colors“ inside the spectral locus differently than humans. I know of no shipping camera that meets the Luther-Ives condition. This means that cameras exhibit significant observer metameric failure compared to humans. The camera color space differs from a more common working color space in that it does not have a unique one to one transform to and from CIE XYZ. This is because the camera has different color filters than the human eye, and thus "sees" colors differently. Any translation from camera color space to CIE XYZ space is therefore an approximation.
The point is that if you think of camera primaries you can come to many incorrect conclusions because cameras capture spectrally. On the other hand, displays create colors using primaries. Primaries are defined colorimetrically so any color space defined using primaries is colorimetric. Native (raw) camera color spaces are almost never colorimetric, and therefore cannot be defined using primaries. Therefore, the measured pixel values don't even produce a gamut until they're mapped into a particular RGB space. Before then, *all* colors are (by definition) possible.
Raw image data is in some native camera color space, but it is not a colorimetric color space, and has no single “correct” relationship to colorimetry. The same thing could be said about a color film negative.
Someone has to make a choice of how to convert values in non-colorimetric color spaces to colorimetric ones. There are better and worse choices, but no single correct conversion (unless the “scene” you are photographing has only three independent colorants, like when we scan film).