Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: kenoli on December 22, 2015, 02:42:19 pm
-
Most of my printing involves the printing of artwork, both reproductions of artwork and working with an artist to modify a hand painted original.
I have a persistent problem matching blue colors, especially a large area of blue, like a sky.
There seems to be a shift from "turquoisish" to "purplish", i.e. blue + green to blue + red.
I am generally working with a scanned image and am printing to an Epson P9000, though I have had exactly the same experience with an Epson 9900.
I typically make printer and scanner profiles using a X-rite i1Pro spectrometer and software.
I am not completely sure if the problem arises in the scanning or the printing, but I think it is in the printing. I have my monitor profiled pretty well and generally the printed output corresponds fairly well with the color of the image on the monitor.
I can usually correct this (though it takes some work) using a combination of hue/saturation and levels in photoshop. Sometimes it requires adjusting the blues in hue saturation and sometimes the cyan. In levels, it involves adjusting the blue, of course.
It is always a challenging and persistent issue and I haven't found a set of layer settings that I can apply universally.
I'm wondering if others have any relevant experience with this issue that they can share with me.
One friend who has this trouble thinks it is due to the lack of any "true" blue ink in the Epson ink lineup. Epson does include orange and green inks and with the P9000 commercial version includes a violet that they say expands the blue gamut some, though we declined the violet ink as it requires switching out the LLK ink permanently which Epson says is not a good idea. The Violet was added for proofing applications where the pantone colors have to be matched exactly.
I am wondering what result I could have gotten if I did use the violet option.
I have a pretty good set of scanner and printer profiles that reproduce most other colors fairly accurately, with little required color correction.
Any help would be appreciated.
--Kenoli
-
These Epson printers can produce any hue and tone of blue that you require. That isn't the problem. It sounds like a profiling or a scanning issue. What was the original media? What scanner and scanning software are you using? How was the scanner profiled in respect to the media you are using? Is the matching problem coming from the image you see on the monitor in your printing application versus the image from the printer, or is it what you see on the original media versus what you see from the printer?
-
Most of my printing involves the printing of artwork, both reproductions of artwork and working with an artist to modify a hand painted original.
I have a persistent problem matching blue colors, especially a large area of blue, like a sky.
There seems to be a shift from "turquoisish" to "purplish", i.e. blue + green to blue + red.
I am generally working with a scanned image and am printing to an Epson P9000, though I have had exactly the same experience with an Epson 9900.
I typically make printer and scanner profiles using a X-rite i1Pro spectrometer and software.
I am not completely sure if the problem arises in the scanning or the printing, but I think it is in the printing. I have my monitor profiled pretty well and generally the printed output corresponds fairly well with the color of the image on the monitor.
I can usually correct this (though it takes some work) using a combination of hue/saturation and levels in photoshop. Sometimes it requires adjusting the blues in hue saturation and sometimes the cyan. In levels, it involves adjusting the blue, of course.
It is always a challenging and persistent issue and I haven't found a set of layer settings that I can apply universally.
I'm wondering if others have any relevant experience with this issue that they can share with me.
One friend who has this trouble thinks it is due to the lack of any "true" blue ink in the Epson ink lineup. Epson does include orange and green inks and with the P9000 commercial version includes a violet that they say expands the blue gamut some, though we declined the violet ink as it requires switching out the LLK ink permanently which Epson says is not a good idea. The Violet was added for proofing applications where the pantone colors have to be matched exactly.
I am wondering what result I could have gotten if I did use the violet option.
I have a pretty good set of scanner and printer profiles that reproduce most other colors fairly accurately, with little required color correction.
Any help would be appreciated.
--Kenoli
I agree with Mark. The printer is typically capable of printing colors accurately. The area where it is the most difficult to accurately render color is on the scanner side and it is easy to make or apply scanner profiles incorrectly.
A quick check is to scan a ColorChecker card, apply the profile, and load it in Photoshop. Then set the white point and luminance to match the lightest gray patch when read with the I1 Pro. The other patches should have Lab values that are at least reasonably close to that of the ColorChecker or a loaded reference image.
A simple and fast round trip test is to print an image of the ColorChecker from Bablecolor, scan it, then see how close the scanned image matches by looking at the actual Lab values in Photoshop.
I'm assuming you are using Absolute Colorimetry for reproduction work since this prints the actual colors while Relative Intent scales things so Lab(100,100,100) will be the actual white point of the media and that can be quite different. A Lab value of (50,0,0) should print and measure within +/-2 for each of the 3 numbers. Usually it is within +/-1.
-
These Epson printers can produce any hue and tone of blue that you require.
Blues shifting magenta is an old and rather common problem, just one wart found in Lab which is often used as the PCS. Lab assumes that hue and chroma can be treated separately yet, experimental results indicate that our perception of hue varies with color purity. Mixing white light with a monochromatic light does not produce a constant hue, but Lab assumes it does. This is noticable in how Lab deals with blues, and is the source of this blue-purple shift.
-
Blues shifting magenta is an old and rather common problem, just one wart found in Lab which is often used as the PCS. Lab assumes that hue and chroma can be treated separately yet, experimental results indicate that our perception of hue varies with color purity. Mixing white light with a monochromatic light does not produce a constant hue, but Lab assumes it does. This is noticable in how Lab deals with blues, and is the source of this blue-purple shift.
While perceived hue changes with the luminance in the blues and red-oranges, the OP should not see such a change since the reproduction should match the artwork luminance it is a reproduction of. That is, the reproduction and art Lab values should measure quite close. If they appear differently, then they will not measure very closely.
-
Andrew, yes I too have heard of that issue, but if this is a generic problem, why do I get perfectly satisfactory blue skies in the photos I make and print, whether scans from old film or from numerous digital cameras? And unless we have the OP's image to analyze (I don't see it anywhere) I'm not sure one can presume there is a generic problem at play here.
-
While perceived hue changes with the luminance saturation in the blues and red-oranges, the OP should not see such a change since the reproduction should match the artwork luminance saturation it is a reproduction of. That is, the reproduction and art Lab values should measure quite close. If they appear differently, then they will not measure very closely.
EtoA: Corrected. The hue shift perceptual effect is relative to color saturation.
-
Andrew, yes I too have heard of that issue, but if this is a generic problem, why do I get perfectly satisfactory blue skies in the photos I make and print, whether scans from old film or from numerous digital cameras?
Because we have better color engines that attempt with some success to account for this old, blue-magenta shifting.
-
OK, so if the OP also benefits from the use of these better colour engines, it tells me we are back to a specific issue he is having, but until we know some answers to the questions I put, it's hard to know how to isolate his specific problem; anyhow, Doug Grey's analytical suggestions would make useful starting points.
-
Yes, we need a very low rez version of the image in it's working space to load into ColorThink, build a ColorList, plot it's gamut and run it through the output profile too. This isn't much different from the other thread going on here with issues reproducing blues. In that example, we (I) got an image in the working space and was able to plot it and show it's way outside the gamut of the Epson printer.
-
Yes, we need a very low rez version of the image in it's working space to load into ColorThink, build a ColorList, plot it's gamut and run it through the output profile too. This isn't much different from the other thread going on here with issues reproducing blues. In that example, we (I) got an image in the working space and was able to plot it and show it's way outside the gamut of the Epson printer.
No doubt you were able to make that determination, but at the same time, all these pro printers have enough gamut to reproduce very satisfactory blue skies; could it be that he needs to play with the R.I? Perhaps between RC and Perceptual there would be a substantial difference in the handling of the OOG blues?
-
No doubt you were able to make that determination, but at the same time, all these pro printers have enough gamut to reproduce very satisfactory blue skies; could it be that he needs to play with the R.I? Perhaps between RC and Perceptual there would be a substantial difference in the handling of the OOG blues?
That's certainly a possibility! Certainly with a perceptual rendering intent.
-
Blues shifting magenta is an old and rather common problem, just one wart found in Lab which is often used as the PCS.
Only if you are clipping at L*a*b* constant hue lines. If this is within gamut, then L*a*b* is not the explanation.
-
I think the first order of business is to clarify whether the OP is printing scene referred images. This is done for accurate reproduction work and is the norm for scanning then printing, but it is pretty awful for normal photography. The blue hue shift is a real issue for the latter because normally colors are more saturated with more contrast and that can cause a hue shift.
However, none of this applies to reproduction work. A Lab(30,0,-30) will be perceived to have a hue shift compared to a Lab(30,0,-60) whether they are printed or on the original artwork. The Lab values on reproduced art should be made as close as possible to the original art. The only time a hue shift difference between the two is when a color is outside the printable gamut and is mapped to something printable. That could be happening but my guess is that the major issue is the scanner profiling and application of the profile. This is an area where it is easy to get it wrong. It isn't as simple or accurate as making and using printer profile.
-
I think the first order of business is to clarify whether the OP is printing scene referred images. This is done for accurate reproduction work and is the norm for scanning then printing, but it is pretty awful for normal photography.
http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf (http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf)
By Karl Lang
Page 3:
The capture of scene-referred data is a science. The printing of output-referred data is also a science. The translation of an image from scene-referred to output-referred is the art of photographic printing. The original scene must be interpreted to produce a print. This process is subjective; there is no single “right way” to do this.
Page 7:
If you send scene-referred data directly to a printer, or even a high quality computer display, you will not be very happy with the result. Even using the lightness-mapped data will provide a at, lifeless image. These media don’t have the dynamic range that’s encoded in the original scene; in fact, far from it.
Page 8
Trying to reproduce the dynamic range of our original scene-referred image within the dynamic range of print isn’t possible.
In order to create a photographic image that evokes some resemblance to the original scene, we need to compress some parts of the tone scale and stretch others. We may also use clipping on at least one end. Clearly this process is both subjective and image-dependent. There is no universal right way, no formula or curve that will work for every image.
-
I have a persistent problem matching blue colors, especially a large area of blue, like a sky.
There seems to be a shift from "turquoisish" to "purplish", i.e. blue + green to blue + red.
This sort of problem is usually pretty straightforward to figure out, if a little tedious. Track the color through your workflow.
[ Your biggest problem may be that you don't actually know what your workflow is in a technical, color numbers sense, and/or you are unfamiliar with the tools needed to do this. ]
i.e. Pick a uniform reference patch in the original. Measure it with your instrument. Scan it with your scanner.
Check the delta E and the error direction between what you measured and what the scanner profile predicts it will be using Absolute colorimetric. If that looks OK, move to the next step in you workflow.
If you are doing (say) a relative colorimetric to relative colorimetric conversion from scanner to printer then:
Convert the scanner RGB to relative (PCS) L*a*b* using the scanner profile relative colorimetric forward table. Convert that number to the printer "RGB" space using the printer profile relative colorimetric backwards table.
Check the printer profile invertibility/clipping by running that RGB forward through the printer profile using relative colorimetric, and check the resulting L*a*b* against the one you put in above.
Print a patch with that RGB. Measure it with your instrument.
Use the printer profile to convert the printer RGB to Absolute colorimetric L*a*b* using the forward table, and check the delta E to what you measured on the printer.
That's about it really. The source of your problems should show up there somewhere.
If the above indicates there is no problem (the delta E's are small and don't compound), then perhaps there is a difference between your actual workflow and the above manual one. You can do a similar exercise by comparing various values between files through your actual workflow and the manually calculated numbers.
Typically I would use ArgyllCMS icclu to do these profile conversions (of course!) - but maybe other tools could be used if they are more familiar (ColorThink ? Photoshop if you configure it properly ?).
-
Going back to square one for a moment, the OP still hasn't told us what the original media is, what scanner is being used and where the profiles come from. The original media is important to know about because there is a substantial difference in the handling especially of Blue between Kodachrome and all other chromes. If scanning Kodachrome, it is best to use specific profiles for Kodachrome. To makes those, a Kodachrome target is needed. Those are now as scare as hen's teeth and cost a fortune. I believe there are some Kodachrome emulation algorithms available that circumvent this problem. Between flavours of other chromes there are differences of colour rendition that are best served with bespoke targets. Then there is the scanner. Depending on the quality of the scanner, the consistency and accuracy of colour rendition could be an issue as well. A number of variables could be affecting the colour matching between the painting and the print right from the scan stage, before one even gets to how OOG colours are handled. It would be helpful when those looking for assistance provide as much relevant information as possible. It makes proposing useful answers more prospective.
-
http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf (http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf)
By Karl Lang
Page 3:
The capture of scene-referred data is a science. The printing of output-referred data is also a science. The translation of an image from scene-referred to output-referred is the art of photographic printing. The original scene must be interpreted to produce a print. This process is subjective; there is no single “right way” to do this.
Page 7:
If you send scene-referred data directly to a printer, or even a high quality computer display, you will not be very happy with the result. Even using the lightness-mapped data will provide a at, lifeless image. These media don’t have the dynamic range that’s encoded in the original scene; in fact, far from it.
Page 8
Trying to reproduce the dynamic range of our original scene-referred image within the dynamic range of print isn’t possible.
In order to create a photographic image that evokes some resemblance to the original scene, we need to compress some parts of the tone scale and stretch others. We may also use clipping on at least one end. Clearly this process is both subjective and image-dependent. There is no universal right way, no formula or curve that will work for every image.
I agree with all of that so your point is what?
You do realize (I hope) that the process of scanning and printing to reproduce the scanned article is done using a scene referred process.
If a friend gives you a 4x5 borderless print and asks you to enlarge it to an 8x10 the proper way to do it is to scan it with a scene referred profile. Resize it. Then print it using Absolute Colorimetric Intent. As long as the print media has a gamut that is as large as that in the scanned image there is no art to it. Just the science and the numbers.
The OP is scanning something and wishes to reproduce it. A good scanner profile and AC printing is the best way to do it.
-
I agree with all of that so your point is what?
You do realize (I hope) that the process of scanning and printing to reproduce the scanned article is done using a scene referred process.
If a friend gives you a 4x5 borderless print and asks you to enlarge it to an 8x10 the proper way to do it is to scan it with a scene referred profile. Resize it. Then print it using Absolute Colorimetric Intent. As long as the print media has a gamut that is as large as that in the scanned image there is no art to it. Just the science and the numbers.
The OP is scanning something and wishes to reproduce it. A good scanner profile and AC printing is the best way to do it.
Yes, and I think this makes all the more sense insofar as the OP indicates these are scans and prints of photographed artwork - (likely paintings?), which would have far fewer gamut issues than photographs of the great outdoors. At least blue values in the original art should be generally amenable to measurement, which would indicate the existence of potential gamut compression issues straight away, once compared with the gamut limitations of the printer/paper profile discernible in Color Think Pro.
-
Going back to square one for a moment, the OP still hasn't told us what the original media is, what scanner is being used and where the profiles come from. The original media is important to know about because there is a substantial difference in the handling especially of Blue between Kodachrome and all other chromes. If scanning Kodachrome, it is best to use specific profiles for Kodachrome. To makes those, a Kodachrome target is needed. Those are now as scare as hen's teeth and cost a fortune. I believe there are some Kodachrome emulation algorithms available that circumvent this problem. Between flavours of other chromes there are differences of colour rendition that are best served with bespoke targets. Then there is the scanner. Depending on the quality of the scanner, the consistency and accuracy of colour rendition could be an issue as well. A number of variables could be affecting the colour matching between the painting and the print right from the scan stage, before one even gets to how OOG colours are handled. It would be helpful when those looking for assistance provide as much relevant information as possible. It makes proposing useful answers more prospective.
This is very true for the most precise colorimetric replication. Other than that you just have to spot check colors with a spectro and hope you're are close enough.
-
Going back to square one for a moment, the OP still hasn't told us what the original media is, what scanner is being used and where the profiles come from. The original media is important to know about because there is a substantial difference in the handling especially of Blue between Kodachrome and all other chromes. If scanning Kodachrome, it is best to use specific profiles for Kodachrome. To makes those, a Kodachrome target is needed. Those are now as scare as hen's teeth and cost a fortune. I believe there are some Kodachrome emulation algorithms available that circumvent this problem. Between flavours of other chromes there are differences of colour rendition that are best served with bespoke targets. Then there is the scanner. Depending on the quality of the scanner, the consistency and accuracy of colour rendition could be an issue as well. A number of variables could be affecting the colour matching between the painting and the print right from the scan stage, before one even gets to how OOG colours are handled. It would be helpful when those looking for assistance provide as much relevant information as possible. It makes proposing useful answers more prospective.
You got me thinking a bit. Because of the limited dye set for wet processes, the math to fix up the scanner output should be fairly simple and you don't need many patches because the spectral characteristics should be just a linear combination of the dyes. It's a much simpler problem than trying to fit a CFA response to a large number of natural colors. Simple regression should produce quite accurate results. Likely a simple matrix would map the colors correctly to D50. At least if there are only 3 dyes in the wet process. If there are more dyes than that one would probably need to use LUTs.
A simple picture of a colorchecker printed using the wet process would be more than enough. One measures the print with a spectro and that becomes the target to extract the dye responses from.
-
Wow! What an amazing array of responses. It is going to take some sorting through to give them justice, and, I think a bit of learning on my part to fully understand all of them.
I am scanning with an Epson 10000XL. I have made scanner profiles using the i1Pro device & software and with Vuescan and, in the end have found that I get the best results with the profile that Apple loads for that scanner.
I am scanning reflective RGB and scanning a variety of sources, mostly original artwork and it is the latter that offers this challenge. The artwork I am working with currently involves a few media, including traditional watercolor paintings on watercolor paper, mixed media on flat matte paper made up of a range of media from oil pastel to pan pastel to collages to watercolor. The fields of blue watercolor in the mixed media and the traditional watercolor are the areas that give me the most trouble.
I will try some of the tests proposed, to the point I actually understand how to do them and report back. I may not get to it until after Christmas. I do have a color checker target and a collection of Wolf Faust targets that I use for making scanner profiles. Vuescan actually offers a process for making profiles all the way from the scanner to the printer that I haven't tried.
I greatly appreciate the thought and time all of you have put into this.
--Kenoli (the OP)
-
OK, this is starting to clarify. You can have difficulty with this kind of scanning because the reflective properties of paint on paper seem to differ enough from what the profiling targets' colors have been configured for that accurate profiling becomes very difficult. I have heard of this problem before and the only viable solution I've read has been workarounds using editing tools either in the scanner software or in the post-scan editing process. (I know one technically savvy photographer/artist who tried to produce a profiling target using the pigments of the painted media, but as I recollect it was not a good solution - perhaps I can check with him and refresh my memory of this - it was years ago.) Hence the absence of a good profiling solution for this particular kind of scanning adds manual intervention and time, but off hand I don't know of a viable alternative.
I assume of course that you were using a reflective target to make a profile for a reflective scanning process. That is essential, if it is to work at all.
You may not be satisfied with the quality of results from a Pro-level printer if you are using a scanner as the reader of the printer profiling target, if that is what you meant by Vuescan offering a complete profiling solution from scan to print. So if you haven't spent time on this, that's fine.
-
I'm sure he isn't using the scanner to profile his printer. He said he uses an I1Pro and software for making scanner and printer profiles.
However, applying scanner profiles correctly is tricky to the point I gave up and wound up just assigning the scanner profile after loading the unmanaged scan in Photoshop. One way too make sure the profile is used properly.
Your points about the difficulty scanning media with irregular surfaces, especially lumps with glossy surfaces. Profiles are all made with 0/45 spectros and I have no idea how well the scanner replicates that geometry. And the artwork surface geometry is another factor to make life difficult. Watercolor art should be ok though. Probably his best bet is to check the color accuracy by following GWGill's post. Once that is verified he should be able to see whether the scanner will be adequate for artwork.
-
I'm sure he isn't using the scanner to profile his printer. He said he uses an I1Pro and software for making scanner and printer profiles.
However, applying scanner profiles correctly is tricky to the point I gave up and wound up just assigning the scanner profile after loading the unmanaged scan in Photoshop. One way too make sure the profile is used properly.
Your points about the difficulty scanning media with irregular surfaces, especially lumps with glossy surfaces. Profiles are all made with 0/45 spectros and I have no idea how well the scanner replicates that geometry. And the artwork surface geometry is another factor to make life difficult. Watercolor art should be ok though. Probably his best bet is to check the color accuracy by following GWGill's post. Once that is verified he should be able to see whether the scanner will be adequate for artwork.
True Doug, he is not using the scanner to profile his printer. He just mentioned what appears to be that that as an option in Vuescan and I responded that it's iffy in principle.
I think the character of the reflectance (influenced by the factors you mention here) plays a role in how well a scanner and profile combination can deal with colours in painted media. I agree one should expect watercolour to be less challenging than some other paint media, but not necessarily - could depend on the kind of watercolour and what it is painted on.
The workflow options of scanning with the correct profile at the scan stage, or applying the same scanner profile to a "raw" scan in Photoshop produces identical results from my testing, provided the scanning application itself is amenable to good colour management. As you would imagine, I use SilverFast Ai Studio 8.x and have found either option equivalent.
-
Further on this subject, to refresh my memory of discussions with highly experienced and knowledgeable practitioners from years gone by, I pulled up this response from one of them who will remain anonymous "to protect the guilty"; we were talking about how to work around the problems of accurate painting reproduction using cameras or scanners with conventional profiles. I think these comments are relevant and insightful in this context:
<<Just a remark here about what we discussed a few years ago on the subject of ** Using the actual artist's colors and building a profile based on those colors ** I'm talking specifically about watercolor ...
<<1- Measuring off the artist painting is pointless because the spectrophotometer scans only a minute part of the pigments that make up the color, these are not representative of the color that our eyes perceive (I did extensive tests of that and sent you samples of my tests, I'm not sure if I have kept them).
<<2- So you must photograph or scan the art then [ >Select ] a larger area of the color and [Filter>Blur>Average] that color ... and then you are no longer measuring the *original*. You are measuring a bad photograph displayed on a screen possibly using a bad profile ...
<<I *did* build sets of hundreds of patches (of diminishing intensity) using a brush and the *actual pigments from the artist*. That did not help much because the artist in question always used a *mixture* of two or more pigments together.
<<I am now of the opinion that if the camera could capture all the colors accurately and "equally" then an accurate reproduction would be achievable using Lightroom and Photoshop.
<<I agree that accurate lighting and good profiles are important but they will not get you close enough to an accurate reproduction of the painting unless you do a *lot* of tweaking with Photoshop.>>
The discussion back then focused on both scanning and camera capture, but more the latter; the basic problem posed by the reflectance characteristics of the original media was seen to be of a similar character.
-
Further on this subject, to refresh my memory of discussions with highly experienced and knowledgeable practitioners from years gone by, I pulled up this response from one of them who will remain anonymous "to protect the guilty"; we were talking about how to work around the problems of accurate painting reproduction using cameras or scanners with conventional profiles. I think these comments are relevant and insightful in this context:
<<Just a remark here about what we discussed a few years ago on the subject of ** Using the actual artist's colors and building a profile based on those colors ** I'm talking specifically about watercolor ...
<<1- Measuring off the artist painting is pointless because the spectrophotometer scans only a minute part of the pigments that make up the color, these are not representative of the color that our eyes perceive (I did extensive tests of that and sent you samples of my tests, I'm not sure if I have kept them).
<<2- So you must photograph or scan the art then [ >Select ] a larger area of the color and [Filter>Blur>Average] that color ... and then you are no longer measuring the *original*. You are measuring a bad photograph displayed on a screen possibly using a bad profile ...
<<I *did* build sets of hundreds of patches (of diminishing intensity) using a brush and the *actual pigments from the artist*. That did not help much because the artist in question always used a *mixture* of two or more pigments together.
<<I am now of the opinion that if the camera could capture all the colors accurately and "equally" then an accurate reproduction would be achievable using Lightroom and Photoshop.
<<I agree that accurate lighting and good profiles are important but they will not get you close enough to an accurate reproduction of the painting unless you do a *lot* of tweaking with Photoshop.>>
The discussion back then focused on both scanning and camera capture, but more the latter; the basic problem posed by the reflectance characteristics of the original media was seen to be of a similar character.
Most interesting.
I prefer to do reproductions using cameras rather than scanners for many of the reasons above. The exception being where I need precise dimensional control. Photographs have to be dimensionally mapped and corrected for lens and illuminant levels. This is pretty easy for a fixed setup where you have a reference illuminance image. Then a short Matlab script does the adjustments.
These aside, what photography allows that scanners don't is control over the angles of illumination. My preferred setup is two lights on both sides at 45 degrees to the object as this closely matches the way profiles require spectrophotometer measures. This usually works but sometimes you can get reflections from surface features you won't see if, say, the art is displayed from above with a 30 degree illuminant angle. With cameras, you can change the illumination positions to avoid much of that.
The Luther condition is a problem with both scanners and cameras but more so with scanners because the combination of the color filters and the scanner's ragged spectrum makes color rendition worse.
I recall a paper that showed camera CFAs can be made to match Luther conditions much better by using 3 photographs, two with different colored filters. The RAW file color channels from each image can then be processed to provide much more accurate XYZ values. It should work pretty well with the right filters but I never tried it and never really had the need for the increased accuracy the technique would provide.
-
I know of no shipping camera that meets the Luther-Ives condition. This means that cameras exhibit significant observer metamerism compared to humans.
http://dougkerr.net/Pumpkin/articles/Metameric_Error.pdf
-
I know of no shipping camera that meets the Luther-Ives condition. This means that cameras exhibit significant observer metamerism compared to humans.
http://dougkerr.net/Pumpkin/articles/Metameric_Error.pdf
That's right and it hasn't really improved over the years. The paper I was referring to used several color filters in addition to an unfiltered image to effectively improve closeness to Luther-Ives. It was published quite some time ago. I believe the person was working with the Rochester folks. It's been a while so I could be wrong on that.
I just read the article you linked. It's quite a good explanation and overview of the issue. Thanks.
-
Everyone:
I continue to be overwhelmed by the thought and skill shown in the replies to my query.
I am greatly appreciative though not sure what next steps to take since a lot of this is beyond my knowledge level. I'm fascinated by the conversation and would like to understand everything better than I do.
I would greatly appreciate a suggested process in words a much less knowledgable person (that is, me) can understand that would either help solve the problem or give you more information that would help move the discussion along towards a solution. I'm willing and anxious to learn. I do have a color checker target and did read through the babble color website, to some degree. I'm not sure if I need their $250 software or not to follow suggestions related to their site.
I will add a bit of info here that might be helpful:
1. I am perceiving the shift from blue (on the turquoise side) to blue (on the violet side) largely from what I see on the monitor to what I see coming out of the printer. This occurs both from images I have scanned and images artists bring to me. The primary artist involved, however, is bringing me images that he digitized with a scanner. I do have his originals for comparison. For others, I don't know the source of the images.
2. I have carefully profiled the scanner, monitor and printer, all three with i1pro and the scanner with other devices as well. The problem with the i1pro scanner profiling process is that it requires a scan of a target (I am using wolf targets) and I am not sure exactly how to get a scanned image that is not already affected by the scanner driver. VueScan has a process they say will do this as well as the Epson Scan driver, though I get quite different results depending on which I use to provide the image to i1pro. In the end, I have found that I get the best results with the scanner profile provided through Apple's operating system (not sure who provided it to them or how it was created).
3. Other than the blue issue, I am getting pretty good color pass through all the way from the scanner to the printer.
4. I have a t3i camera, and some soft boxes that provide lots of light. I have decided to use the scanner instead of the camera as I commonly need much better resolution than I can get from the camera. In the artwork I do with my partner, we commonly enlarge scans many times and images shot with the camera are inadequate. I also had serious color challenges using the camera input, but that was before I really knew how to manage color inputs from a camera. I now have some tools to help with that, including color checker and some Expodisc filters, though color checker is pretty much keyed to Lightroom, with which I have little experience. The scanner has been a simple solution and I can scan large artwork in sections and stitch it together in Photoshop and have them at high resolution.
5. I do have the Adobe Lightroom software (CS6), though I have only looked at it briefly and do not use it. I have been using Aperture to organize my images but use Photoshop CS6 to edit images. Everything is upside down in the Aperture world at this juncture.
I can provide any other info anyone would like.
Again, I appreciate the thought and time people have put into this. I seem to have struck an interesting topic.
--Kenoli
-
I continue to be overwhelmed by the thought and skill shown in the replies to my query.
There are a few things you could try before it gets too complicated.
1. How's your lighting? If it's not controlled and it's fairly yellow (most indoor lighting is) then your blues may appear purple.
2. Work on isolating the problem. Try printing known-good images with similar blues and see if they shift. (Andrew Rodney has a great test image for such colors). Also try scanning a known good image (more difficult to get your hands on) to see if blues shift on it. Isolating the problem is the key.
-
You have an I1 Pro. First establish that your monitor and printer profiles are operating correctly. The monitor profiling software should ensure that. Second, make a few blue/purple patches in an image in Photoshop using Lab color space. Print them out using Absolute Intent, then measure them with the I1 Pro. The Lab values should be very close to the colors you made the patches in the image. The important thing is that the measurement of the patches match the Lab values you entered to create the color patches because their appearance can differ a lot due to illuminant differences from the monitor's setup.
Basically, you want to check each component of your workflow for accuracy. Andrew Rodney has some good tutorial videos on how to adjust monitors to match your print viewing. It's important to also do this if you want what you see on a monitor to match what you see on a print but the most important thing is to be able to print a defined color accurately and that has nothing to do with the monitor side. It's entirely a function of the printer and profile being set up correctly.
Once these are working then the next step should be to verify or fix the scanner profile. Divide up the issues and address one at a time. Trying to get everything "right" without using instruments to measure each aspect separately, is a hard and frustrating process.