Troubleshooting Photos –
About Color Management
Electronics stores have an odd habit of displaying shelves of TV's all tuned to the same channel. It's odd, because the colors on the sets always differ, sometimes markedly, which makes you wonder how they would look at home. In reality, it's only because they're side-by-side that you notice the differences, so you'd adapt to and be happy with almost any of them. They do, however, illustrate a significant problem in picture reproduction – all devices vary in the way they reproduce color, and the slight variation you can see in supposedly identical TV's or monitors from the same factory balloon to major differences when you compare the colors rendered by different manufacturers' photo printers, paper and inks.
As a further illustration of this variation, the next time you're in a store with a selection of photo paper from different manufacturers, try comparing them side-by-side – each will have a slightly different interpretation of "white". Since the paper's definition of white affects the printed photo (along with other, less obvious differences such as the way different types of paper absorb ink and reflect light), a change in your paper-buying habits will force you to make changes in the way you prepare photos for printing – as will the purchase of a different brand of ink or a new printer. Adapting to a new printer or new paper by trial-and-error methods can be such a hassle that most of us will put off trying a new printer or paper, even when what we're using no longer really works for us.
Color management offers a way around this problem. Instead of a lot of trial-and-error, we get to do a bit of systematic work, culminating in right-the-first-time color (it may or may not be perfect, but it will be very close), and this cuts out a lot of the frustration. Instead of preparing color images individually for various media, a publisher can optimize the photo once, then publish to many media with different color requirements, without having to individually fine-tune the image for every medium. And if that sounds too high-end for your needs, consider that many of your photos may be both printed and shared on photo-sharing sites – multi-media publishing on a small scale, but multi-media publishing by any definition.
Incidentally, color reproduction gets very complicated once you go beneath the surface, so thinking through some of its concepts can make you feel like your head is on fire. We're not going there. This is a brief guide with a bit of background, but more of an emphasis on understanding why you make certain practical choices, followed by application-specific guides to doing it.
A very brief history
In the late 1980's, color printing was rapidly displacing black-&-white in newspapers and magazines, and many people understood that some form of publishing to computers was on the horizon (CD-ROM was the hot ticket; the Internet didn't open up to commercial publishing until 1995). Publishers realized that to make it happen, they would have to find a way around the old labor-intensive publishing methods, which were expensive and slow. Those methods relied on the color judgement of highly trained people – but color perception, even in well trained color specialists, is complicated by a number of physical, psychological and environmental factors, so people are not good judges of color, and their decisions can be skewed by such factors as adjacent colors and tones, light levels and even such seeming irrelevancies as whether the viewer has a cold (see this entertaining site for scientifically-based illusions that demonstrate that the characteristics that help our visual system make sense of the world around us also render it "not very good at being a physical light meter").
Although current processes then relied more on skilled hands and eyes than science, the science was in the wings, waiting for its close-up. For many decades, light and color had been quantified in ways that dovetailed neatly into the requirements of computers. Moreover, as the publishing industry was then second only to the auto business in size, and everyone agreed on what they wanted, there was clearly a lot of money to be made – always a good incentive to get ideas out of the lab.
The CIE 1931 chromaticity diagram that indicates all human-visible light. (This diagram indicates colors, because no monitor can show all the colors that people with full color vision can see and a monitor is what you're looking at.) More on this diagram, along with linked explanations of many color concepts, can be found here.
There are only three practical matters you need to know about this diagram: 1. It represents all colors visible by humans in numerical terms – which is what makes color management possible on computers. 2. All the digital devices you possess reproduce only a portion of this diagram (the triangle in monitor shows the approximate relative portion that your computer can display). 3. All those portions are different, sometimes massively but always significantly, which is why we need color management.
Visible light is a range of wavelengths within the electro-magnetic spectrum, and the colors that make up visible light are normally described in terms of their wavelength. The world is not colored by pure wavelength; most colors around us are combinations of several wavelengths. The needs of different trades or professions inevitably led to the creation of many ways of describing color, but scientists early recognized the value of turning a subjective description into an objective one, and agreed on ways to describe color as a set of numbers. The diagram above is a common representation of the visible colors quantified in 1931 by the CIE (in English, the International Lighting Commission). If you open the color chooser of your photo-editing application, you may see three or four ways of representing color but ultimately, these representations are numerical, and numbers are something that computers handle with ease.
Having color in a computer-friendly form was a massive first step, but to implement color management at a practical level and make multiple-media publishing a reality, there were two broad problems that had to be addressed.
The first is the difference between the color range (or gamut) available with different reproduction technologies. Additive color (RGB or monitor color) has a vastly greater gamut than Subtractive color (CMYK ink or print color). Monitors can display almost 17 million colors without breaking a sweat, while CMYK is limited to about 100 thousand in a good magazine and 10 thousand or less in a newspaper (if the monitor number seems high, consider that a healthy young person with good color discrimination can see about 100 million colors). In addition, the monitor and print ranges both include colors and tones that are unavailable within the other set of colors.
Moreover, within each of those categories of monitor and printer, every device is different, not only between different models or from different manufacturers but every individual device. Your old Whizzycolor 100 printer is not only different from your new Zowiecolor Pro Printer, it's likely to be a bit different from any other Zowiecolor Pro Printer. And once we start playing around with third-party ink and paper combinations, anything is possible.
Both of these issues did get solved, and because there were strong financial incentives on both sides, the solutions are very accessible, being platform-independent and standardized internationally. Shortly after color management first appeared in the early 1990's on Apple computers as ColorSync, the International Color Consortium (ICC) harmonized file formats and methods across software publishers and computer platforms, thus avoiding the sort of mismatches and pointless differences that marked early publishing software (one remaining pointless difference: on a Mac, a profile is suffixed .icc, but on Windows, .icm; otherwise the files are identical and you can move a profile from one platform to the other simply by changing the suffix).
At the time the ICC was founded, digital photography was just an unbelievably expensive idea. Digital photography has grown now to the point where digital is the norm, film is the exception. Unfortunately, color management was for a long time in the hands of people who treated it as an opportunity to form a secret society rather than as route to hassle-free good color. That seems to have changed. Color management in image-editing software seems much more transparent and there are more options aimed at casual photographers. The result is that you can use your computer's built-in color management capabilities with manufacturer-supplied profiles for $0.00, or characterize and profile your own system for between US$100.00 and US$300.00 (the differences are outlined later).
How it works
Color management depends on two processes, called calibration and characterization.
- Calibration is the process of getting a device to do what it says it's doing, so when a monitor is told to display a specific value of blue, it will display precisely that blue and not something else – an essential starting point for color judgments. Calibration isn't the whole answer. You can vary the color displayed by a monitor, but some color devices can't be modified so easily – you can't tweak an ink color unless you happen to be its manufacturer, so you need...
- Characterization, which is a process of recording the range of colors that a scanner can scan or a printer can print (its gamut). In addition, characterization includes recording the difference between the input color (the color in the image that the scanner is scanning or in the file that the printer is printing) and what the scanner or printer produces (despite calibration, there always will be differences between ideal output and the colors actually achieved, and this must be allowed for).
- The key to a practical solution is to produce a table of adjustments that nudge the picture's colors in a direction that pleases you (a process that is a little more complicated than it sounds).
To characterize a printer/ink/paper combination (each of which makes a significant contribution to the final color you see printed):
1. First, you print a page that includes patches of different colors at varying degrees of saturation (the top half of the picture below). To this printed page, you attach the standard target that came with your color management software (the bottom half of the picture below). You then scan the assembled page. Your color management software reads the colors scanned from the standard target and compares those colors with the values that should be present (in effect characterizing the scanner). It then reads the sample you printed, using the scan of the supplied target to factor out inaccuracies in your scanner. From that information, it calculates the color value that was given to the printer, what came out and what correction values should be applied to each color to ensure that what gets printed is the color that was called for. The resulting file, which has been called a 'table of differences', is the profile for that combination of printer, ink and paper.
Paper choice makes a huge difference in the way color is rendered on paper, but color management can even out many of the differences. The top half of card was printed on uncoated print-your-own-greeting-cards paper; the top half of photo was printed on coated semi-gloss photo paper. The lower portion is an international-standard IT8 target included with the colorimeter and software to provide an accurate color reference when the complete page is scanned.
After the page was scanned, the page scan was analyzed by the color management software. By comparing the colors that were printed against what should have been printed, the color management software creates tables that compensate for the differences. These tables, called profiles, were then used to print the photo below.
2. When you print to a color-managed printer, your operating system filters the picture information through the profile you select and adjusts all colors so that the colors that are printed more closely resemble those in the source photo.
The characterization/correction process is rather like the correction you would do if you were driving a car with a speedometer that reads high – you want to drive at 60, but you know that an indicated 60 is more like 55, so you drive at an indicated 65 to be closer to a real 60. The only difference is that color management software is doing similar conversions on the fly for the entire spectrum of millions of colors, subtly tweaking them up or down to reflect the image's intent.
Color management lets you get good results the first time, even with paper that is less than ideal for photo printing. This photo was printed using profiles made with the IT8 target shown above. The only modification is scaling to this size. ph-cms shows it on photo paper with color management on. cd-cms shows it on matte, very porous greeting-card paper with color management on. cd-no cms shows it on the same paper with color management off.
ph-cms looks exactly like the original seen on screen. cd-cms has lost color and contrast but is recognizably the same picture (the print looks very much better than the scan because the scanner picks up paper texture that isn't noticeable in the print). The loss of color and contrast make cd-no cms scarcely worth looking at, either in the original print or on screen.
Where color management gets interesting is in deciding what to do about colors that are out of gamut), or outside the range that a printer (or other device) can reproduce. The most obvious examples are fluorescent colors, deep purple or a really rich yellow, all of which are unavailable on monitors and which require special inks to print. They must be changed to a color the monitor or printer can deliver; whether this is done by changing the one color alone or by subtly altering the entire photo depends on the rendering intent.
There are four rendering intents, but only two are much used in photography.
- Saturation (sometimes called Graphics in Windows) tells the printer to shift unprintable saturated primary colors to the nearest primary colors it can cope with. Saturation is intended only to preserve eye-popping color, such as those used in pie-charts and other business graphics.
- Absolute colorimetric (Match in Windows) matches printable colors exactly and clips the unprintable ones to the nearest ones that it can handle. This sounds good, except that the absolute colorimetric intent makes no allowance for changes in the white point. If you were to print on a slightly yellowish paper, for instance, the blues might creep toward green, the reds toward orange.
- Relative colorimetric (Proof in Windows) is more useful because it makes allowance for the color of the paper (assuming you had profiled the printer with that paper) and adjusts all colors to deliver printed color identical to the source color. The relative colorimetric intent still clips out-of-gamut colors to the nearest in-gamut colors, which can mean loss of detail, but if you have a photo whose colors are all in gamut and you want exact color matches, it is a good choice.
- Perceptual intent (Picture or Image in Windows) is the one most commonly used for photography. Perceptual intent doesn't maintain absolute color fidelity; rather, it works to maintain the relationship between colors. Out-of-gamut colors are shifted to the nearest in-gamut color and all other colors are shifted to the degree that is needed to keep them distinct from adjacent colors. The result is that all colors in the picture may be shifted somewhat, but the overall appearance of the picture is maintained with all detail intact.
Rendering intent affects the way out-of-gamut colors are translated into the printer's gamut. When perceptual intent is chosen, all colors are altered, even those that are in-gamut, to preserve the relationships between colors. The two greens in the upper corner of the triangle, for instance, will remain a lighter and darker green when shifted in-gamut.
If relative colorimetric intent is chosen, out-of-gamut colors are translated to the nearest in-gamut color. In-gamut colors remain unchanged. Colors like the two greens in the upper corner of the triangle may end up being almost the same color. Although this could sacrifice some detail, relative colorimetric may be the right choice for some photos, particularly if you need faithful rendition of in-gamut colors.
What about color spaces?
Color spaces provide descriptions of the colors available to the device used to record or work on the picture and these may cause you some confusion. Point-&-shoot cameras can record in sRGB; DSLR's can record sRGB, Adobe RGB and sometimes ProPhoto (but sRGB is almost always the default).
sRGB was developed by Microsoft and HP to encompass all the colors displayed by a normal good-quality monitor. As such, it comprises approximately 35% of the human-visible spectrum. This doesn't sound like much, but experts regard it as quite sufficient for most applications.
Adobe RGB was developed by Adobe to encompass the range of first-class color photo printers driven by RGB devices. It improves on sRGB's color gamut in three areas: fairly significantly in cyan-greens, somewhat in intense magentas and oranges, and a bit in dark greens.
Comparisons between sRGB and Adobe RGB are often shown as triangles on the CIE 1931 diagram with sRGB's triangle very much the smaller; this is a misleading comparison caused by an over-representation of greens in the 1931 diagram that makes Adobe RGB look disproportionately large, much in the way that a Mercator map inflates Greenland almost to the size of Africa (Africa is 13 times the size of Greenland).
Choosing the right space is not just a matter of 'more is better'. Color imaging does not have an unlimited budget – for any given bit depth, there is a pre-determined number of discrete colors that can be represented, whether you're working in sRGB or Adobe RGB. Since those discrete colors are more widely separated in Adobe RGB than in sRGB, there is a greater risk of posterization or banding in Adobe RGB. That risk – which is not present in all photos – is worthwhile if a specific image needs the additional colors it provides. Sunset shots or rich foliage might well benefit from Adobe RGB, but only if you can print into the range that it offers (and on the Web, whose default color space is sRGB, these richer colors will seldom be seen).
Remember that while Adobe RGB addresses the gamut covered by RGB printers, only the best color photo printers can print to that broad a range. Prints made at a chain store often don't even cover the sRGB gamut; to see the full Adobe RGB range, you'll need a pro-quality printer. You will probably be better off optimizing your prints for the printer (or printing service) you use than blindly using Adobe RGB in the expectation that it will magically make your prints better.
Acquiring color management capabilities
Digital photography came of age after color management had become accepted in the graphic design and printing industries, so color management should have been thoroughly established in photography right off the bat. In fact, support is uneven; some printer manufacturers support it comprehensively and openly, others rather grudgingly. However you can still improve your printer results by using color management. If you're willing to pay for a color management hardware/software package, you'll get first-class results. If you want to skip the expenditure, you can improve on your present results by using the variety of free tools and profiles now available.
The first step is getting color you can rely on from your monitor (a few monitor basics to consider are given in the context of viewing this site). Mac users can get very good results from OS X's own monitor calibrator when you use it in expert mode (basic mode isn't much help). Windows users can use the free and very capable QuickGamma 2.0 or Adobe Gamma, which is included with Photoshop Elements (including the trial edition). Note that these visual calibrators are only as good as the eyes of the person doing the setup; if your color discrimination isn't good or you're too idle to clean your glasses once a month, buy a colorimeter.
Once you have a reliable monitor, your next move is to discover what sort of color management possibilities are available for your printer – but first it's important to distinguish between ICC-based color management that happens in your image-editing program, and your printer's proprietary color management system that occurs within its printer driver. The instructions provided by this site provide methods based on turning off your printer's proprietary color management system and relying on the ICC capabilities within the image-editing program, an approach which is both more powerful and less prone to error. Under no circumstances should both systems be turned on together.
If you have a printer that came out after 2004 (or for which a new printer driver was issued since that date), chances are good that the printer driver includes ICC profiles. These may be aimed at using the printer with specific types of paper from that printer manufacturer, they may be generic, such as 'ink jet paper' and 'premium photo paper' or they may be a mix of both. Both Canon and Epson are coy about ICC color management, though less so about their proprietary versions of color management – but the information and profiles are packaged with the drivers or available from their Web sites and they claim their profiles are good enough that there is no need to make your own. HP, who brought out one of the first proprietary versions of color management, seems to have embraced the ICC and offers good information, both general and printer-specific. (Links change frequently, so use the corporate site addresses and search for 'color management' for a wealth of information.)
To extend your range a bit, you can download ICC profiles from such photo paper manufacturers as Kodak, whose paper/printer profiles are in the Pro support section with all their color management info (search 'icc profile photo printer', and Ilford. A quick search on Google for 'paper ICC profile' will turn up a number of sellers who offer unusual, sometimes less expensive papers and profiles that work with the paper and specific printers. For example (and these are just examples, not recommendations):
If you are not satisfied with manufacturer-supplied profiles or you want to try different combinations than are offered and you don't mind spending the money (from about US$60 for a colorimeter alone to $300 for a complete package), consider buying your own standalone color management colorimeter-&-software package to calibrate and profile your system yourself. You will probably be well pleased with the results. Look for packages from Datacolor and X-Rite – both sell various combinations that include colorimeter, IT8 target and software, two or one of these items. Don't be dismayed if you land on a page with very expensive products – most color management companies make extremely pricey equipment for professional and scientific purposes, but they also make consumer-level gear – just keep looking. Large photo stores and on-line sellers like Amazon also carry color management packages. You need a colorimeter to calibrate a monitor, and the IT8 target and software if you want to do your printer paper (you also need a scanner, or access to one).
Getting the details right makes a difference. Printer was accidentally printed using a generic profile for the printer in use; too much of all colors and specifically too much blue was laid down, making the gold green in the shadows. Printer + is a profile for the printer and paper used, and is a very close match to the on-screen original.
What you need to buy depends on your ambitions.
If you want only to calibrate your monitor, it's now possible to buy a colorimeter with software for under US$100.00.
If you want to calibrate your monitor and characterize your printing system (recommended, as the complete solution has the greatest impact on your print quality with the least fuss), a colorimeter, IT8 target and software package is available for under US$300.00 (you will need a scanner or access to one).
How various devices reproduce color, represented within the horseshoe-shape of the CIE diagram above. The point of these illustrations is not to show that one device is better than another, but to show the huge, sometimes wild differences in the way these devices represent color. Before color management, the only way to make a photo look equally realistic when the capabilities are so different was through costly tweaking by skilled operators. Color management lets you and me get results that make us happy.
cmyk is what commercial printing presses use for papers and magazines – a limited gamut compared to others, but satisfactory when handled correctly. s rgb and adobe rgb are two color spaces used for monitors, digital cameras and printing (see above). scanner is a good-quality slide scanner, cd scan is a popular slide-scanning service and camera is a good digital SLR.
Plugging and playing
Actually using color management is quite simple once you've done it a couple of times (which is the whole point), but it's nice to have a guide for the first forays. If you're using Photoshop, there are no better guides than the essays provided by photographer Ian Lyons. Moreover, he posts them for versions from Photoshop CS3 to 7, Mac and Windows. Get the right version, because Adobe changed its mind about implementation several times, then print it and walk yourself through the process.
This site provides instructions for:
- Photoshop Elements 3, 4 & 6 for Mac OS X;
- Photoshop Elements 3 for Windows XP;
- Photoshop Elements 4 for Windows XP;
- Photoshop Elements 7 for Windows XP;
- Paint Shop Pro Photo X2 for Windows XP.
Whether you are using free solutions or a full color management package, be careful to turn it on at the application/program level (normally preferred, but some recent printers insist that you use their internal system) or the printer level, but not both. Otherwise you will end up with a seriously mis-colored print. Also remember that printer profiles are specific to the settings for which they are made. If you change the paper, or to a lesser extent the print resolution, you will see color shifts, sometimes dramatic ones.
The virtue of a little do-it-yourselfing. The first image, again representing a color gamut within a wire-frame version of the CIE human-visible range, shows a generic ICC profile for a photo printer with its maker's ink and paper. The second shows the custom profile made with a widely available profiling package. The differences in the prints made with the two profiles are subtle, but the custom profile delivers a definite improvement.
The other, greater advantage of do-it-yourself profiling is that you have more freedom in choosing printer, ink and paper combinations. For example, printer makers will give you profiles for their printer with their inks and their paper, but if you want to color-manage your printer with someone else's ink and paper, you must make the profile yourself.
