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Archive 2012 · ICC vs OMS?
  
 
Rodolfo Paiz
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p.1 #1 · p.1 #1 · ICC vs OMS?


Hi!

Getting into large-format printing now. I understand that the OMS files are paper presets to be installed into the printer so the printer knows how to print on each new paper type.

What I don't understand is why some paper profiles also include ICC files. My monitors are calibrated properly with an i1 DisplayPro, which I thought produced the ICC file (which, in turn, I thought was the color-calibration profile for the monitor). Do I also need another ICC file? If so, why? Or should I simply ignore the other ICC files?

What am I missing here?



Apr 13, 2012 at 05:14 PM
BobCollette
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p.1 #2 · p.1 #2 · ICC vs OMS?


In an optimally color managed environment, you would have an ICC profile for each device in your system that handles color, i.e. your monitor, scanner, and printer. The ICC profile describes how each device handles color. For instance, a scanner or camera profile would describe what "color" each RGB code value coming out of the scanner or camera produces. Likewise with a printer, the ICC profile describes what code values to send the printer to produce a certain color. In a color managed environment, the image data that is passed from device to device is not RGB or CMYK code values, but rather colorimetric data, hence the need to know what a device's color characteristics are (how to convert to/from color values to code values).


Apr 13, 2012 at 06:11 PM
colinm
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p.1 #3 · p.1 #3 · ICC vs OMS?


The OMS file describes only the printer settings—it doesn't contain any data about how the paper interacts with the ink to reproduce color and tone.

The OMS file is just stuff like "increase the platen gap", "use photo black", "set the feed speed to 5", and "don't apply gloss optimizer."

The ICC file is what makes the screen translate to the print.



Apr 13, 2012 at 08:18 PM
Rodolfo Paiz
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p.1 #4 · p.1 #4 · ICC vs OMS?


Thanks, guys.

Hmm... I think I get it. So I guess I need an ICC file for the screen, and then an ICC and OMS pair for each printer/paper combination. Is that accurate?



Apr 13, 2012 at 09:14 PM
colinm
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p.1 #5 · p.1 #5 · ICC vs OMS?


Yep, you've got it.



Apr 13, 2012 at 09:30 PM
Rodolfo Paiz
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p.1 #6 · p.1 #6 · ICC vs OMS?


Thanks!


Apr 13, 2012 at 11:24 PM
Alan321
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p.1 #7 · p.1 #7 · ICC vs OMS?


Make that one for each printer/paper/dpi combination.



Apr 14, 2012 at 06:39 AM
cgardner
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p.1 #8 · p.1 #8 · ICC vs OMS?


In RGB the "recipe" for obtaining neutral colors is simple, just mix equal parts R=G=B. Due to the nature of the pigments/dyes and how they interact with the paper, and the reflective character and color of paper things aren't that simple for printing in CYMK.

ICC profiles are ideally custom made from a test print of 900 color patches generated from a standard file of known RGB values. The analysis of the that test print defines what the maximum satutration of the colors are on that printer. A 255,0,0 red file value will be more saturated on one printer/paper combination than another.

Perceputally the saturation of the darkest colors and the white of the paper base calibrate our vision for what to expect as "normal". For example in a photograph of a model in a red dress is holding a grayscale target under her chin the viewer will expect the dress to look very red (more intense than any other red in the scene), the skintone and color to be free from any warm/cool or green/magenta biases, and every step on the gray scale to look neutral as on the original she was holding.

What the profile does, in effect, is create the "recipe" for C+Y+M that will make the steps of the grayscale neutral — gray balance — and ensure that the mix of CYM in the skin and dress reproduce both similar, in terms of overall relative impression of the color visually, on the print. When it works correctly it's like the automatic transmission in a car, you don't really need to think about shifting the gears, you just press down the gas pedal and steer.

When you buy a printer it has profiles for its firmware / driver for all the printer brand papers. When you print letting the printer manage color and select paper type from the print dialog that tells the printer which one of the standard profiles to use, depending on the type of paper. Those profiles are "generic" in the sense they are not custom generated on that printer with a specific lot of paper and ink, but since the manufactuer controls all the variables they usually produce acceptable results perceptually — the print of the woman in the red dress holding the gray card would seem normal in terms of color balance.

If you print on a paper other than one for which a profile is stored need to do one of two things: use a third-party profile and print with Photoshop managing the color, or use the closest "canned" profile per the datasheet provide with the paper letting the printer manage manage the color. The latter method allows people with less sophlisticated applications to print using the profiles in the driver and get acceptable looking results but is only as good as the match of the paper characteristics to one on the printer driver selection menu for your printer. But the driver menu usually has the option to "tweek" the characteristics when the printer is managing color.

Where you are likely to first interact directly with the printer profile if you choose to "shift the gears" manually is when "soft proofing" the file on your computer using the printer profile. Soft proofing is a simulation which shows how color and contrast will change in the printer's gamut vs. that of the calibrated screen. The file in soft proofing mode will usually look less saturated and flat vs. the normal screen image in some colors because the printer paper / ink gamut is smaller in those colors. The Catch-22 with soft proofing is that you are only seeing manipulated rendering of the printer's gamut via the "window" of your printer's gamut. Turning on the Out Of Gamut Warning will gray out areas in the image which the soft proofing isn't displaying accurately.

Soft proofing is useful to the extent you have made enough prints and compared the results to interpret what it is trying to tell you about the limitations of the printer vs. screen gamuts. The quickest way to get an understanding of how accurate soft proofing will be is to first make a print before editing it, then compare that baseline print with the appearance same file in soft proof mode on screen. The closer they match the more you can trust the soft proofed image on screen to predict results when editing the colors of the image. For example it makes little sense to boost the saturation in reds it the file to make the red dress more intense if the printer/paper/ink is already making it as red as physically possible. Pushing the reds beyond that will begin to adversely affect the tone of the skin and other lighter colors containing percentages of yellow and magenta the printer uses to create them.

The profiles you get with the paper are "generic" in the sense that they were generated on a printer similar to yours and will be a close, but not perfect match to your printer. But because of how the human brain adapts to color close is good enough in most cases. The best way to test how well the profile is working is to print a standard test file with a wide range of colors and known neutral objects like a gray scale. Print the standard with various settings and compare them to each other, the file in soft proof mode, and the file in the normal viewing mode and you'll quickly get your bearings on how the various settings / options affect results and which is producing what you consider the best results. That ultimately is a personal, subjective decision only you can make by comparison. As they as YMMV. :-)



Apr 14, 2012 at 11:46 AM
Rodolfo Paiz
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p.1 #9 · p.1 #9 · ICC vs OMS?


Good Lord, Chuck... thank you. Let me read that through a few times and I'll get back to you once I figure it all out.


Apr 15, 2012 at 04:43 AM
Peter Figen
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p.1 #10 · p.1 #10 · ICC vs OMS?


Rodolfo

"What I don't understand is why some paper profiles also include ICC files. My monitors are calibrated properly with an i1 DisplayPro, which I thought produced the ICC file (which, in turn, I thought was the color-calibration profile for the monitor). Do I also need another ICC file? If so, why? Or should I simply ignore the other ICC files?"

You monitor calibration is really a two step process. First, you use your i1 to calibrate - which sets the monitor to a known set of values - like 6500Kelvin, 120cd/m2, gamma 2.2, etc. The second part is the software making the monitor profile itself, which is the file that describes the calibration to applications that can use it.

You didn't mention which brand or model of printer you're planning on getting, but it's probably going to be either Canon or Epson. In the case of Epson, there are presets for different paper types in the printer driver, where you can choose any of the Epson branded papers. Those settings will load different ink loads and what are called linearization settings into the driver as a starting point for the subsequent printer profile for the paper being used. In order for the printer profile to work correctly, you have to use the same media setting when you print as was used when the profile was made. That give you the same base starting point and helps guarantee consistent color ever time.

In order to make color management work to give you consistent and predictable color, you need a minimum of two profile in play - you need a source profile and you need a destination profile - and in addition, if you want to see an accurate screen rendition, you need a monitor profile as well. The source is always your working space - usually an RGB working space like sRGB, Adobe RGB, etc., and the destination will be your printer profile. Since the RGB values of the working color space don't match the RGB values of the printer, the profiles act as a translator between the two languages, converting Spanish to French, if you will.

You can have canned profiles provided by printer or paper manufacturers or you can make or have made custom profiles that take into account your specific printer. The canned profiles are free, but often are less than perfect. The canned profiles that Epson provides for their own media have been getting progressively better over the last few years and are really very good now. The big problems come when you want to print on third party papers. You need custom profiles for the best results.

Please, please, do not get to invested with the previous poster's long overly complicated post. While there is some valid information in there, there's also a lot of outdated stuff that will only confuse you and pretty much anyone else that tries to read it. I really don't want to go point by point down the list, but let's just say that Chuck gets modern inkjet printers a bit confused with the offset presses he used to work with.

Just remember that unless you're going to be using a true CMYK RIP (raster image processor) even though your printer does use CMYK plus other inks, you don't treat it as a CMYK printer. The standard printer driver assumes that you are sending RGB files, never CMYK. The driver itself provides a "black box" conversion to the printer inks colors as it passes the data to the printer, but it expects to get RGB data in.

There are a few of us here on this forum that have years of experience printing on large format inkjets. It's not that hard but there are a few things to watch out for. it's great fun and you can actually make a fair amount of money doing it as well. It's amazing how fast the word spreads that you have a large format printer and people start wanting large prints from you.



Apr 15, 2012 at 10:17 AM
 

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Peter Figen
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p.1 #11 · p.1 #11 · ICC vs OMS?


"In RGB the "recipe" for obtaining neutral colors is simple, just mix equal parts R=G=B. Due to the nature of the pigments/dyes and how they interact with the paper, and the reflective character and color of paper things aren't that simple for printing in CYMK."

This is only true for artificially created, gray balanced, abstract RGB working spaces, but not for actual device spaces, and, unless someone is printing through a true CMYK RIP (i.e. ColorBurst) you never consider CMYK when printing to an inkjet.

"ICC profiles are ideally custom made from a test print of 900 color patches generated from a standard file of known RGB values. The analysis of the that test print defines what the maximum satutration of the colors are on that printer. A 255,0,0 red file value will be more saturated on one printer/paper combination than another. "

Where did you get the 900 patch number from. Remember the old Linocolor offset profiles were from 210 patch charts, while the standard ProfileMaker RGB chart is 918 patches and the standard CMYK chart is close to 1500 and in Measure Tool, you could create charts with up to 10,000 patches. The newest Profiler software seems to like 1728 patches, but you can use ColorPort to generate whatever patch count you want. The tradeoffs are that the more patches, the greater the accuracy but often at the expense of smoothness, while too few patches leave the profiling software with too much interpolation to do if you have a non-linear device with bumps or dip in tonal response.






"Soft proofing is useful to the extent you have made enough prints and compared the results to interpret what it is trying to tell you about the limitations of the printer vs. screen gamuts. The quickest way to get an understanding of how accurate soft proofing will be is to first make a print before editing it, then compare that baseline print with the appearance same file in soft proof mode on screen. The closer they match the more you can trust the soft proofed image on screen to predict results when editing the colors of the image. For example it makes little sense to boost the saturation in reds it the file to make the red dress more intense if the printer/paper/ink is already making it as red as physically possible. Pushing the reds beyond that will begin to adversely affect the tone of the skin and other lighter colors containing percentages of yellow and magenta the printer uses to create them."

You typically don't make test prints of unedited files before you edit them unless you're using a completely uncalibrated monitor and can't reliably see what you file really looks like, and if your screen isn't calibrated, you effectively can't do soft proofing, so the whole question becomes moot. The whole idea of calibration is that you CAN make edits to color and contrast before printing because you monitor actually does give a reasonably reliable rendition on screen that lets you do that. All it takes is a few prints of edited files to see the correlation and pretty soon you won't even be thinking about it. The one thing to really watch in soft proofing is whether you actually need to check the "paper white" or "black ink" boxes, as these previews are often not nearly as accurate as leaving them unchecked - particularly when printing to photo papers. They're a bit better when previewing matte papers and canvasses. You'll be surprised at just how close to the screen good photo papers print, without any soft proofing at all.



Apr 15, 2012 at 10:38 AM
cgardner
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p.1 #12 · p.1 #12 · ICC vs OMS?


You never need to consider CYMK when printing exactly because the profiled based management handles the translation automatically, similar to how in a car with auto transmission you don't need to think about shifting. But it only works ideally if the printer profile is accurate.

How does one determine if a profile is accurate?

If one makes a print BEFORE doing any editing based on what is seen on a calibrated monitor one can see more objectively how the appearance of the color values in the file differ from the appearance on screen, both in normal and soft proofing with that printer's profile. I would call that process one of "calibrating" expectations of what the printer gamut is capable of.

After making dozens or hundreds of prints the traits of a printer will become obvious and once aware of the difference, large or minor, most will incorporate corrections into the workflow. All I was suggesting is shortening the learning curve by of "calbrating expectations" by doing a few contolled test with known neutral content like a gray scale in a test shot.

If the photo is a woman in a red dress you'd have difficulty seeing any gray balance error in the profile driving the printing process. Having her hold a gray scale and color patch target in the photo would make it easier to see the differences by virtue of being able to easily lay the actual targets used in the photo over the orint for direct comparison.

The same hold true for monitor calibration. Spend $300 for a calibration tool and use it to calibrate the monitor and brain having faith in the technology then trusts what is seen by eey as the "correct" color. But what if some operator or system error doesn't perform the calibration process correctly. How would one know? If for example in incorrect calibration process created a slight green bias your eyes and brain when looking at the monitor will adapt to it and not see it. That's the reason you want a neutral wall around the computer. Taking a break from staring at the monitor screen and looking at the wall will "recalibrate" color perception of the brain. So while you might not see a green cast after staring at an image, you will be more likely to notice it after "recalibrating" perception by looking away at the netural wall.

One of the reasons I set Custom WB at capture whenever possible, and include gray card and color target in a test shot after setting it, is so when I first open the image I know the from the baseline of my camera the color is technically neutral and I should not see any color cast in the neutral content.

Most scenes don't have neutral content to evaluate. If shooting woman sitting on a red car in a parking lot without any reference target it might be easy to spot a green bias due to a monitor calbration error when opening the file because the tires and pavement you expect to be neutral look green. But if the shot was instead taken on grass under the shade of a tree there may be a combination of problems, not technical, but human perceptual variables, in play. The first is the fact the lighting will have a green bias the viewer usually will not be aware of when shooting. Without any control target a photographer using Daylight WB will produce a file in the camera which faithfully records the green bias they didn't realize was there. When they get home and open the file on their perfectly calibrated monitor and look at the file expecting the netural content to look neutral, their eyes will adapt to the monitor image and they will not detect the green bias there either.

I've seen that scenario in hundreds of photos posted on forums here. A outdoor photo under trees taken with Daylight WB will have more saturated green foliage, which looks good, but dull gray human skintones resulting from green light on the warn toned skin. The lighting will appear flat — low in contrast. Why do they post photos that way? Their brains adapt perception when looking at the calibrated montor. The problem isn't the camera, or the montior, it's the fact human color perception adapts.

Taking the scenario to the next step, printing, what will happen? The file might look perfectly balanced on screen, but when printed the print will show the green bias that is actually there. Why? Because the printer doesn't have a brain driven by expectations and memory of what things look like. It will simply take the RGB values in the file, green bias included, and reproduce them accurately per the printer profile.

Change the scenario slightly. Have the woman next to the card hold a gray card and MacBeth color target, but still shoot with Daylight WB. When opened on the computer the eyes will adapt and not notice the green in the car or woman, but it will be more likely to notice the bias in the neturals of the gray card, or notice that the greens seem more saturated and reds duller on the MacBeth target than normally seen and expected in a daylight shot. Adding the target gives the brain a known set of objects to "recalibrate" to. Having a neutral wall and room lighting similar to the white point of the monitor works similarly. After staring a a shot with a lot of green grass in it for 5 min. your color perception will get biases. Taking a break from the screen and looking at the wall you "trust" as neutral send your brain to a "neutral corner" which will allow you to see the color more objectively when next looking at the monitor.

Setting Custom WB works similarly. In the under tree scenario if Custom WB was set on a gray card held in the green biased light the camera will add the needed + magenta correction to make the card and content neutral at capture. It will not affect the recording of the RAW values but will tell the calibrated monitor to add the same + magenta correction when displaying the image.

When setting Custom WB in camera in essense you are shifting what you trust as the "accurate" color from the monitor to the camera. Let's assume for the sake of example the monitor calibration got messed up or has drifted since the last calibration. Open an image with a Grey Card shot after setting the Custom WB and you would expect it to be R=G=B. Expecting that to be true you will see the card as neutral even if the monitor has a bias. How can you see if the screen has a bias? Click the card image with the correction eyedropper tool.

If a monitor is calibrated correctly there shouldn't be a color shift on the card or photo content in a Custom WB shot. Exposure may shift if the card isn't exposed close to its relfective value, but the colors shouldn't shift. Including the MacBeth color chart and the gray card in the test shot makes it easier to see any color shifts when that simple test is done. What that with the card also does in the event the montor calibraion isn't 100% perfect is to make the image under consideration appear as is would in terms of gray balance on a perfectly calibrated monitor.

With the simple expedient of setting Custom WB and then verifiying it with the eyedropper tool the file as opened will be technically neutral and be displayed neutral, taking the variable of adaptive human perception of color out of the loop. "Trust" regarding what is correct color shifts from what is seen on the montior (from the baseline of thinking it is perfectly calibrated) to trusting the fact that camera will set Custom WB correctly off the gray card. The difference? The camera WB baseline can be verifed with the eyedropper test on the card.

How do you verify your montitor calibration i correct? Compare it to the camera baseline. Take a subject outdoors on a clear sunny day free from any reflected color casts and have them hold a gray card and color chart. Take a shot with Daylight WB. Use that shot to set Custom WB off the card in the center circle of the viewfinder (Canon cameras). Comparing the two frames will show you any difference between the Daylight WB baseline in camera on a clear day vs. Custom WB. They should be similar in appearance and eye dropper values on the card. Open the files on the computer. Do the "click test" on both. If the camera did WB correctly the card should be R=G=B and no shift in color will be seen. Open the file in Photoshop or whatever you use with your normal workflow but make no changes based on appearance and print it as you normally do. Compare the print with the actual targets the subject was holding.

That's a test you only need to do once to evaluate montor and printer. The image of the target on the print will likely not be an exact match to the colors in the chart but the neutrals in the chart and gray card should be a match if the printer profile got the "recipe" for convering RGB neutrals to CYMK neutral correct on your printer / paper combination.

If you get in the habit of including standard targets in your test shots whenever you encounter problems you can't figure out you can make a print the test shot from that session with the targets in similar a similar manner, then lay out that print, your baseline test print, and the actual targets and compare the differences. Since there would be no user modifcations in the loop based on monitor appearance any changes between the two prints would logically be the result of some variance in the printing due to different batch of ink, paper, change in printer calibration, user error (wrong profile selected), etc.

Without standard targets in the workflow it is difficult to objectively see or solve workflow problems. Even when Custom WB isn't practical, a shot of the card and target in a test shot with eye dropper correction when opened gets you to the same neutral baseline for starting the editing process. If as suggested you make a print at that point you can see what changes in print appearance are due to the screen / printer gamut differences more objectively than after tweeking contrast and saturation. The baseline print becomes a road map to show you what needs improvement.

I'm not suggesting you do that with ever photo you print, but if you've never tried the ideas suggested here you might find trying them at least once edifying in a way you can relate to and verify with your eyes by direct comparison. A quirk of human perceptiion is that it adapts rapidly to any single gamut it is exposed to, but presented with two different images it will detect even minor differences between the actual targets and the print and screen images of the them.



Apr 15, 2012 at 12:34 PM
Rodolfo Paiz
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p.1 #13 · p.1 #13 · ICC vs OMS?


Finally worked through all this... thanks for all your help, and pardon the delays as I do my homework.

My new printer is an HP Z3200 in the 24" variety. HP, Epson, and Canon all make fantastic printers, but the HP's built-in i1 spectrophotometer is a huge differentiating factor. My old B9180 had a densitometer, and as long as I stuck to HP papers it never made a bad print in its life. I could just finish an image to my satisfaction on the monitor, hit print and it was good. With the Z3200, I hope to be easily free to use any favorite paper while having the printer calibrate itself accurately for that paper.

Amazing how much better the tools have gotten over time. Right now I need to fix a software glitch that isn't letting me create new paper presets on the printer. I'm using canned profiles from Ilford and Hahnemuhle in the meantime; but they only have OMS files, hence the original question. Then I need to create a camera profile in Lightroom. Once I get both camera and paper set up properly, I should be 99% of the way there.



Apr 16, 2012 at 01:24 PM
cgardner
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p.1 #14 · p.1 #14 · ICC vs OMS?


What a camera profile will do is allow you to more accurately reproduce the MacBeth color chart, but in practical terms that's not an important goal for pictorial photography.

There are two elements to managing color: gray balance/linearity over the tonal range and selective color. Selective color in a digital camera is controlled via styles. Styles selected in camera don't affect the RAW values captured, but they will change the appearance when displayed. For example here's a MacBeth chart shot in RAW with the Style changed in PP:







Notice how the style choices shift the colors but the neutral column isn't changed? That's the difference between gray balance linearity and selective color control. What a custom profile of the camera will do is give you a custom style, which will produce a closer match between the print of the photo of the target when the two are compared. That would be useful if you shoot clothing for catalogs and need to show the customer what that green pair of pants will look like when they get them. But for most other photography its more a matter of trying different styles and see what works best — changing the color selectively, without screwing up the neutrals.

I use ACR and open my test shots contain the control targets using the Camera Calibration tab as show in this screen shot below. Abobe when adding cameras to ACR shoots a color target with the camera styles then recreates the same values selectable via the pull down menu on the right. If you create a camera profile using the DNG editor and load it, that's the screen in ACR where you would apply it to your RAW image data. It will change the appearance of the file in the same way changing styles will, shifting colors but not altering the neutrals on the chart.







Since I set Custom WB at capture the grays are neutral. Selecting different styles from the menu will shift the colors but not affect the neutrals. For example here's the shot with Landscape applied...







As you can see from the charts above Landscape increases saturation in primary reds, greens and blues which isn't the best choice for a portrait. The fact I have the subject holding a gray card with the MacBeth target on it makes it easier for me to see, by back and forth comparison of the "canned" styles what is changing colorwise while the neutrals stay neutral. Once I find the general color balance I want for the image I can fine tune it using the sliders on the right, save the settings, and apply them to the rest of the images in the batch.

With that workflow color management starts with a technically neutral baseline of Custom WB and using the Camera Calibration tab allows me to keep the neutrals that way while tweeking the color to taste on a bespoke basis image-to-image as the content and implied mood dictate. For most portraits I will usually tweek the skintones warmer than the starting neutral baseline, but occasionally if the mood of the subject or the environmental clues dictate I will shift the bias cooler or a bit greenish on the skin.

YMMV and I don't want to discourage you from doing the exercise of profiling your camera because it will help you understand what I explain above. Color is a moving target influenced by the content of the photo and the desired mood you want to project about subject and environment. Control baselines like custom WB off a gray card, including color charts and profiling the camera are just the "neutral corner" you send your color perception to so it will be more objective when you edit.



Apr 16, 2012 at 02:35 PM
Rodolfo Paiz
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p.1 #15 · p.1 #15 · ICC vs OMS?


I do understand that the camera profile is essentially there only to ensure that the camera and Adobe software are being objective about which particular shade of color I'm shooting, and that the interpretation of color comes later. However, I do sometimes have a problem when shooting certain subjects -- the LucasOil orange biplane comes to mind -- when you want to ensure that you match the color of the real thing and doing so in post is notoriously tough.

Really, in my mind the purpose of calibrating the camera is to ensure that I can get "accurate" color (or as close to it as I can) when I need to. Otherwise, I'm perfectly happy pulling and pushing sliders.

My real concern is to ensure optimum use of resources by learning enough to get my prints to come out near-perfectly-matched to what I see on-screen.



Apr 16, 2012 at 05:44 PM
cgardner
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p.1 #16 · p.1 #16 · ICC vs OMS?


If the paint on the plane exceed the gamut of the printer the printer can't reproduce it "accurately" in the literal sense of putting the print next to the plane, but is that really a problem if the prlnt is never compared side-by-side with the plane?

The plane probably doesn't exceed the printer gamut because logo colors are usually selected with assistance of consultants like Pantone so Lucas color is with the gamut of all advertising media, screen and print, where it will be seen. For example Coke Red can be printed accurately in 4/C offset print ads, and it will match the PMS spot color and the red seen on a TV screen or computer monitor.

As a printing plant manager part of my job was educating designers so they realized every color in the PMS swatch book could not be matched on a CYMK press. Pantone makes a swatch book created from CYMK mixes. I keep a supply of them in my desk and hand one to each new designer. They might want day-glo orange on the cover, but day-glo orange can't be reproduced in CYMK on press.

A real challenge was reproducing fine art which often it created with saturated color beyond press / printer gamuts. It's physically impossible to reproduce them accurately. The best that can be done is to max out the saturation of the printer gamut, secure in the knowledge that absent direct comparison with the painting the viewer will accept it accurate, when it is actually facsimile.

As for matching screen and printer? It is s similar situation. The printer can't physically match the 3D gamut of the screen. Knowing this when I print my goal isn't to match the screen literally, but to max out the gamut of the printer while keeping the neutrals in balance. If it does the print will be accepted perceptually by the viewer irrespective of whether it looks like the screen in side-by-side.

The printer can reproduce some colors the screen can't display accurately and some screen color the printer can't match in absolute terms. But again that's not an issue because absent direct comparsion your brain adapt perception to either gamut and providing the entire gamut of the device is used (e.g. Max 255,0,0 red = 100% magenta + 100% yellow) and it has neutral gray balance ( no abnormal color biases ).

If you print you need to manage color from the print backwards. Print a test file that has a full range an gray balance, then detune your expensive monitor via soft proofing with printer profile so the monitor looks as desaturated and flat as the print looks. You can spend a lot of cash on a wide gamut monitor but it will not allow printer to create any different 100% magenta + 100% yellow than a laptop screen would.

Is the closet possible match of print and screen desireable? Yes. A wide gamut Abobe RGB monitor will more accurately soft proof simulate the printer, but since most ink jets exceed AdobeRGB what is seen on screen will not be 100% accurate in absolute terms. If editing is done in ProPhoto the screen isn't displaying it literally either; the color management renders the editing gamut to fit the screen gamut.







Apr 17, 2012 at 02:51 AM
Peter Figen
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p.1 #17 · p.1 #17 · ICC vs OMS?


"If editing is done in ProPhoto the screen isn't displaying it literally either; the color management renders the editing gamut to fit the screen gamut. "

Are you saying that there is a Perceptual rendering to the screen from ProPhoto to the monitor profile?



Apr 17, 2012 at 03:38 AM
cgardner
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p.1 #18 · p.1 #18 · ICC vs OMS?


I'm saying that what is seen when editing is limited by the gamut of the monitor used for editing.

For example if editing in soft proofing mode with the out of gamut warning on and adjusting saturation in a color you will notice this happen:

Initally as you increase saturation you will see the change on the monitor.

Then you will reach a point where no difference is seen in the image on screen when the slider is moved. That's the point where gamut of the screen is reached but the editing and printer gamut hasn't been. At that point you are "flying blind" in terms of visual feedback from the monitor.

As saturation is continued to be increased a point will be reached where the out of gamut warning kicks in and starts to grey out the colors where the manipluation has forced the color in absolute (i.e. Lab coordinate) terms beyond the limit of the printer's gamut. Any further increase in saturation will increase the Lab coordinates of those pixels (out to the limit of the editing gamut border's Lab coordinates) but it will not increase the saturation of the color on the print because the the physical limit of the printer gamut has been reached.

That of course is not how one would typically edit color, but it illustrates what happens to colors which happen to have more saturation when printed than the screen can display and what the out of gamut warning is indicating.

The opposite scenario is a color for which the monitor gamut is larger in absolute terms (Lab coordinates) than the physical limit of the ink on paper gamut. In that situation you would see the out of gamut warning kick in while soft proofing indicating the limit of the printer gamut has been reached, but if soft proofing is turned off and saturation is increased even more there would be a visible change in what is seen on screen. That is the more misleading scenario because when the color is pushed beyond the limit of the printer gamut the print will pale in direct comparison. So in that sense when you turn on soft proofing on a brilliantly saturated screen image and it turns dull and flat what is is doing in practical terms is lowering the expectation of what the printer can be expected to produce vs. what the monitor in normal mode used for viewing screen images can display.

Back in the days before profile managed color on computers we'd temper the expectations of print clients by separating the image on a transparency then making a proof on the same grade paper and inks that would be used on the production press. That proof wouldn't look as good by comparison with the transparency, or proof created with higher grade paper and more highly pigmented inks, but represented accurately what the client could expect their advertising and editorial subjects to look like in the magazine. Less sophisticated customers wouldn't understand why we couldn't match the saturation of the transparencies, but the more technically knowledgeable ones understood you can't get any more saturation than the ink and paper can deliver. There is of course the option of printing on different inks and paper, which is why today an 8 - 12 color ink jet printer produces much better looking images than the 4/C inkjets of 10 years ago and why a glossy print will look more saturated than the same file printed on a matte surface paper.

In practical terms what matters is the gamut of colors in the scene being photographed and how they relate in absolute terms to the monitor and printer gamut. The editing gamut isn't a factor if ProPhoto is used because because the scene, monitor, and printer gamuts are usually all smaller. When mapped as 3D wireframes it can be seen that the vast majority of the colors in the monitor gamut are also within the printer's gamut...







What that means in practical terms is that those colors will not change much when printed. It is only the most saturated colors that fall outside the other gamut and change. What doesn't show in a comparison of gamuts is where the actual colors in the scene fall relative to the gamuts. Not what the camera records, what is in the scene, like the Lucas Oil color, relative to absolute Lab coordinates which model the range of human vision.

If you put an apple on the hood of a Ferarri and park the Ferarrri next to red fire truck and a 10 year old red Chevy with sun faded paint the scene will have a range of reds, some which fall inside the monitor and printer gamuts, some that don't in absolute terms. But what the cameara captures isn't the color in absolute terms, but rather in relative terms. Exposure control is used to keep the most saturated red in the scene , likely the Ferrari, just at or below clipping (255 in 8-bits). Based on that exposure all the other reds in the scene which are less saturated are recorded as NNN red channel values relative to the exposure of the most saturated red. Pushing exposure beyond the point where the red of the Ferrari reached 255 will make the other red objects have higher values in the red channel, but it pushed too much the added exposure will start decreasing detail and blowing the neutral highlights.

When the image is displayed on screen the birghtest red in the Ferrari is mapped to the brightest red the monitor's profile allows it to display. The calibration process of the monitor ensures that in relative terms of saturation within the monitor gamut the fire truck, apple and Chevy seem less intense to the same degree as when seen in person by eye. The brain of the viewer, not seeing anything in the room more saturated than the red Ferarri on screen adapts to the screen gamut and thinks it matches what was seen by eye.

Wkithout manipulation the file is printed on a glossy printer brand paper letting the printer mangage color at Costco, a 4/C ink jet and an 8/C ink jet. Each printer will map the 255 red in the Ferrari to the most intense red the magenta/yellow ink or dyes can produce. The printer's profile will ensure that the less saturated reds fall in place in relative terms so the relationship between the Ferrari, apple, fire truck and Chevy look similar to what was seen by eye in person. If viewed separtately each will look OK. Viewed side-by-side the 8/C ink jet will look better than the 4/C ink jet and it may look better than the Costco photo print. So in practical terms how good the print looks is mostly a function of convenience and cost. The print from Costco costs 18 cents and there's no overhead because you didn't but the printer. The ink jets? The consumable costs plus the amortization of the printer over the lifespan print output is much higher, more so for the 8/C which has twice as many ink cartridges to buy.

Now take the prints and monitor and put them on the hood of the Ferrari next to the apple. Which red will look best then in absolute terms? Likely the 12 coats of hand rubbed paint on the Ferarri. But if you wait until the sun goes down the monitor image will look better

That's what I mean when I say that color is a moving target and its perception is organic in the brain of the viewer and influenced by external frames of references. You can if you wish spend $4,000 on a monitor and an equal amount on a printer, but absent direct comparison with the montior image or your prints the aveage viewer probably will not see $8,000 worth of difference between your print and one from Costco in terms of color if there isn't a red in sight that is more saturated than the red they see in the photo of the Ferarri. Why? Because they know how red a Ferrari is before they seen the photo. They see the photo and their perception adapts to their expectations.

That's the part of the magic trick that make color reproduction work. If you understand that you can save a lot of money on gear, unless you are a guy like Peter who caters to a very sophisitcated clientelle who have 12 color ink jet prints on their walls for comparison. The Costo print hung on that wall would suck by comparison. But in my house all the prints are made with printers with similar gamuts and the viewers have no idea that a Ferrari can look any redder in a photo




Apr 17, 2012 at 12:44 PM
Peter Figen
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p.1 #19 · p.1 #19 · ICC vs OMS?


Never at a loss for words, eh?


Apr 17, 2012 at 03:07 PM
Eyeball
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p.1 #20 · p.1 #20 · ICC vs OMS?


FWIW, I created a custom profile for my Canon 5D2 for use in LR and ACR and it was totally worth it. Much better skin tones than what I could get with any of the stock profiles and much easier than messing with the Camera Calibration sliders, which are much cruder controls than what is used in the DNG Profile Editor. I am sure the Profile Editor is not perfect either, but I think it has a nice compromise in terms of number of sample points used.

I also think that custom camera profiles can help with color consistency among cameras if that is important to you.



Apr 17, 2012 at 03:21 PM
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