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Color Management 101 (TIP- Print this web page for easy reference.) The Basics
The subject of color management is complex, but I have endeavored to make my discussion of this topic as straightforward as possible. In so doing, I have assumed that you probably have some knowledge of color management already – or you wouldn’t be here. My goal for this website is pretty specific – I want to provide you with the very best custom ICC printer profile possible. To achieve this objective, it is important that you have at least some insight as to why this is important. But in case you don’t… here is a very basic – and brief – discussion of how color management should fit into your digital printing workflow. Here are the three objectives I want to accomplish here:
Help you set up your system to get the very best printing results when you use the profile. There are certainly other pieces in the color management puzzle – especially if you work outside the limited scope I describe here. People who fit into this category would include those who scan photographs regularly and who need an accurate input profile for their scanner. Those who work with printing presses or other highly sophisticated commercial-grade printing equipment would also fit into this category. These cases may require more specific consultation with on-site color management specialists – and this service is far outside the scope of what I offer here. Such comprehensive and exacting services can get very expensive in a hurry! Profiling Your Monitor (Display)
Before you can effectively use a
profile for your printer, you need to calibrate and profile your
monitor. This step is probably the easiest and least
expensive part of developing a color-managed workflow.
Since you have made it to this website, I suspect you have
calibrated and profiled your monitor already. But if not,
it is essential that you do this first. Using a printer
profile is a waste of time if your monitor has not first been
accurately calibrated and profiled. Using a Working Color Space Once you have successfully calibrated and profiled your monitor, you have effectively matched the color from your image’s color space to what you see on your monitor. A Color Space is a defined range of colors – also referred to as a gamut. There are device color spaces and working color spaces. Device color spaces define the range of colors that a camera can see, or that a scanner can scan, or that a printer can print, etc. But working color spaces, such as sRGB or Adobe RGB (1998), are not dependent on the color limitations of any particular device. Instead, they determine the range of colors in which you can work with an image. This freedom from device limitations allows you to obtain consistent image editing results. One of these working color spaces – sRGB – has become prevalent as the normal working environment for internet use. It was created several years ago to provide a gamut that would easily match the display capabilities of conventional display monitors. By today’s standards, sRGB offers a somewhat narrow gamut, especially given the continuing improvements in LCD displays and printer capabilities. But sRGB continues to be the most widely used editing color space for use on the world-wide web. Adobe RGB (1998) is another working color space that has evolved over the last several years, and its popularity can be attributed to the widespread use of Adobe Photoshop products. This color space was designed with a focus on printing, and it offers a wider color gamut than sRGB for this purpose. By providing a wider range of available colors, Adobe RGB offers better color accuracy in printed images, as well as more satisfying tonal detail in shadow and highlight areas. There are many other color spaces in use, and all have their merits. But universally, Adobe RGB (1998) is probably the most widely used image color space. It still offers a color gamut that exceeds the capabilities of even the most state-of-the-art inkjet photo printers available today. For this reason, I would recommend that you set up Adobe RGB (1998) as the working color space for your image files.
Another working color space that is becoming more popular is ProPhoto RGB. You may have already encountered this choice for a working color space, especially if you work with Adobe Photoshop Lightroom. The color gamut of ProPhoto RGB is even wider yet than Adobe RGB, allowing for color possibilities that are even beyond the capability of the human eye to see! Even though this is a more comprehensive working color space, it has its drawbacks -- especially when converting colors to a much smaller color space that will match the capabilities of most printers. The compression or clipping of colors that occurs when making this conversion can cause some pretty squirrelly results. For this reason, I do not recommend using ProPhoto RGB as your image working color space. I still believe that Adobe RGB is your best and safest choice.
With more
and more digital cameras today, you can generate JPG or TIF
images using the Adobe RGB color space right in your camera. But
if you shoot RAW, choosing your working color space will happen
later, when you convert from RAW to JPG or TIF on your
computer. At that time, the working color space you have chosen
for your editing software will also become the working color
space for your converted images. The Target Image
Notice that I mentioned that each color patch on the target image has a specific, measured numeric value for red, blue, and green. This is important. What this means is we are talking about profiling an RGB device -- not a CMYK device. "But my printer uses CMYK inks...," I hear you muttering to yourself. True -- most RGB printers actually use CMYK inks, but the output to the printer driver is in RGB format. The printer driver converts the RGB input so that the printer can put CMYK ink colors on the paper. It sounds confusing... and it is, a bit. The issue is that most desktop inkjet printer drivers are designed to handle RGB input. Despite the ink colors in the printer's cartridges, it is the RGB input to the driver that defines the printer as an RGB device.
As a rule, CMYK printers utilize special software, called a RIP (Raster Image Processing) program, that allows the printer to work with CMYK input. The use of a RIP program adds another layer of technology to the color management work flow, and creating ICC printer profiles for CMYK printers is a more complicated process. I limit my creation of custom ICC printer profiles to RGB printers because of the complexity of working with CMYK profiles. If you are NOT using a RIP program, it is probably safe to say you are using an RGB printer -- NOT a CMYK printer. Equipment and Software for Analyzing the Target Image In order to measure the value of each color patch from the target image(s), I use an X-Rite GretagMacbeth Eye-One (i1) Pro spectrophotometer in conjunction with specialized software, specifically designed to compare the spectrophotometer’s measurements from your target against a reference baseline for the purpose of generating a profile that is unique to your printer, your ink, and the paper on which you printed the target. The Eye-One Pro spectrophotometer is a state-of-the-art instrument that provides consistent readings with great precision. Although the Eye-One Pro can be used as a hand-held device for reading your target image(s), I use it with an “iO” XY-coordinate scanning table, also made by GretagMacbeth. Using these two devices together makes scanning the target color patches a completely automatic function – which is not only faster – but less prone to error, as well. Armed with specific details about your printer, the software you use for printing, the paper on which you print your photos, the ink used to print your images, and other important information about your computer environment – I can then create a profile that will enable you to get the very best results possible from your image printing workflow. Printer Environment Color management specialists often speak of the need for establishing and maintaining a “stable system environment” in which to use your profiles. In a nutshell, this refers to your computer system (PC or Mac) and its peripherals. For our purposes, we define this to mean its output devices – specifically the monitors or LCD displays, and the printers. Once you have created profiles for your monitor and printer, it is essential that you maintain the “status quo” of your system environment from that point forward. If any change is made to this “stable” environment, it is very likely that your output devices will need new profiles.
Your printer is a much more stable output platform than your monitor. Its color characteristics drift off course much more slowly and subtly. For the most part, once your printer has been profiled, it should maintain its color characteristics within acceptable limits for a very long time, as long as you make no changes in the operating environment. This means using exactly the same printer settings, paper, and ink that you used when you printed the target used to make the profile. This is a simple, but critical rule -- it is absolutely essential that every time you print using a particular profile, you must reproduce EXACTLY the same conditions as when you printed the target used to make that profile. As long as you remember this caveat, and maintain a stable operating environment for your printer, your profiles should work consistently for you. But you should be aware of the kinds of changes that may adversely affect your printer’s ability to maintain a stable color output. If you change your printer’s connection to your computer, you run the risk of requiring new profiles. For example, if you upgrade from a parallel connection to USB, or if you switch from USB to Firewire, you may see changes in the color output from your printer. You could also experience problems if your printer is moved from a direct connection to a network. The inks you use probably have an expiration date. Check the cartridge packaging or your manufacturer’s website to see what the shelf life is, and try to stay within the guidelines. Ink that has “expired” may cause color shifts in your printed output, rendering your profiles useless. However, the solution here is not a new profile, but changing to fresh ink cartridges. Upgrading your computer to a new operating system may change the way your printer works. Similarly, be alert for color changes if you upgrade your printer’s drivers. It is always a good idea, when establishing the stable environment you want for your printer, to install the most recent drivers available for your printer and operating system before you print the target image. But always be prepared to “roll back” the drivers to the previous version that you are sure worked with your printer profiles. You may find this to be necessary someday with a driver upgrade in the future. Repairs or maintenance to your printer may make it necessary to acquire new profiles – especially if the problem is with the print heads or the electronics that control the movement of the print heads or the movement of paper through the printer. These kinds of changes to a printer’s fundamental operating characteristics can wreak havoc on your printer’s inherent stability. If you change the brand of ink you use, you will probably need a new profile. It is tempting to make this kind of switch – there are lots of third-party inks available out there, and they all cost less than the manufacturer’s inks intended for use with your printer. I’ve been there and done that. I have since become a firm believer in sticking with the manufacturer’s inks. I experienced very noticeable color shifts and numerous other problems with off-brand inks – just to save a few bucks. But never again.
The driver for your printer was more than likely supplied by the manufacturer, and it is probably unique to your make and model of printer. Unfortunately, each manufacturer’s driver designs are proprietary, and the user interfaces are not the same across the broad spectrum of different printers. Because of this variety, it is impossible to show screen shots of all the different settings for every printer. However, the settings are usually similar, and all of the settings required are generally common to all photo printers. There is a good discussion of the printer driver settings, along with some representative screen shots, accessible from the Downloads page. The choices and settings for your particular printer may vary somewhat from those described and shown in the instructions, but locating and working with these settings for your particular printer driver should not be difficult. Coming to Terms With Terminology
In order to fully comprehend how
color management works with your profile to give you the printed
results you want, you will have to grapple with some new terminology
that will appear on your screen when you start printing with an
ICC printer profile. Not to oversimplify what actually
happens, but when you print using a profile, you are converting
the colors in your image from one color space to another.
The image that has been defined -- probably in Adobe RGB -- must
be converted to the color space that your printer can handle,
and it is likely to offer a different range of available colors
than the original working color space of your image.
Because these two color gamuts do not match, the printing
software needs to know the RENDERING INTENT
you want to use when making this
conversion.
If you choose the Relative Colorimetric rendering intent, the white point and black point of the smaller color gamut -- in this case the inkjet printer -- are matched to the exact same color values of the wider color gamut, Adobe RGB. This means that any image colors that are outside the inkjet printer's color gamut will be clipped -- and image detail beyond the extreme white and black points of the printer will be essentially lost. However, the colors that fall within the printer's range of available colors will match the color values from the image color space (Adobe RGB) exactly. There is one more term with which you should become familiar -- that is BLACK POINT COMPENSATION. This feature is intended for use when you have selected the Relative Colorimetric rendering intent. See the figure on the right for a graphical representation. When you enable Black Point Compensation (BPC) with Relative Colorimetric selected, the black point in Adobe RGB is mapped to the black point of the printer, just as with the Perceptual rendering intent. However, the converted colors at the white end of the spectrum are still clipped, with loss of image detail that is outside the printer's color gamut. So, you retain good shadow detail, but highlights get clipped. You also get closer matching of color values between the two color spaces at the highlight end of the spectrum. There is no set standard for which of these settings to use when printing with a printer profile. It really is a matter of what works best for you. There are some images that will give you better results with Perceptual -- others will do better with Relative Colorimetric and no BPC. And still others will give you better results with Relative Colorimetric and BPC enabled. You will have to try each method yourself to see what gives you the best results. Soft proofing can be a help when trying to make this determination.
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There are
thousands of pages that have been written about color
management, and reading some of them will help you gain an
understanding of the subject – and also help you build a
meaningful color-managed workflow. Here is a list of some
There are
some very good monitor calibration devices and software packages
available: Spyder3 by DataColor (different versions and price
points), also various versions of Pantone Huey, and X-Rite’s
GretagMacbeth Eye-One Display software. All of these
systems include a precision colorimeter device for monitor
calibrations, and software that will help you create a custom
monitor profile. These are the major players, and all
provide very good results at a reasonable price. All of these
systems provide detailed information about the display settings
you should use in order to view your images on your monitor with
uncompromised color accuracy
Once you have completed the calibration of your monitor, you can
depend on your monitor profile to give you an accurate color
display of your images. Now you are ready for the next step –
precisely matching the image colors on your monitor with the
colors in your printed images. This is accomplished by using an
ICC printer profile that defines the way in which your printer,
ink, and paper interact with each other to produce the exact
colors you want in your prints. In order for me to create a
custom ICC printer profile that precisely meets your
specifications, you will have to send me a “sample” from your
printer – called a “target image.” This is a carefully
constructed simulated image that consists of rows and columns of
different color patches – hundreds of them – each one of which
has a specific, measured numeric value for red, blue, and
green. Using very specialized equipment to analyze the target
you print, I am able to compare your printer’s results with what
they should be. The measured variances can then be stored in a
special file – called a “profile” – which your printer can use
to print colors with greater accuracy, and that are as close as
possible to what you see on your monitor.
Your monitor
or LCD display is by far more dynamic and less stable than your
printer – it will change its display characteristics quite
rapidly over a short period of time – sometimes in just a matter
of days. The solution to this problem is simple, however. Just
make it a point to recalibrate and profile your monitor on a
regular basis – once every two weeks or so is probably okay. You probably already
know that this is a quick and simple process. Calibrating and
profiling your monitor takes no more than 10-15 minutes.
So…
basically, any change wrought by you or outside forces that
impacts the way your printer operates may render your profiles
useless. Even something as innocuous as a change in the
humidity of the place where the printer is located can be a
problem. I have read about problems with a printer placed near
a window – with the changing seasons causing different amounts
of sunlight to strike the printer at different times of the
year. So be wary of even very subtle changes in your printer’s
operating environment. If you start seeing shifts in your
printer’s color output, you need to run through the checklist of
everything that might have happened to cause the problem.
The
software needs to know how to deal with the image's colors that
are outside the gamut the printer is capable of reproducing.
There are two rendering intents with which you need to be
familiar, and which are the only ones that have any real meaning when printing digital photographs. One
rendering intent is 
The
longer bar on the left represents the wider gamut of the working
color space -- in this case, Adobe RGB. The shorter bar on
the right represents the color gamut of the inkjet printer,
which is not able to reproduce the full range of colors from
Adobe RGB. If you choose the Perceptual rendering intent,
the white point in Adobe RGB is mapped to the white point of the printer -- and the same happens with the
black point. By doing this, the entire Adobe RGB
color gamut is mapped to the smaller printer gamut, but all the
in-between color values are compressed so that they all "fit" in
the smaller gamut. What this does is ensure that the
shadow and highlight details are retained in the conversion.
However, the exact colors -- especially at the extreme ends of
the spectrum -- may not match up exactly. The colors near
the middle of the spectrum will match up much more closely than
the colors at the extremes.