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ICC Color Management Explained


The final version of the image of Amanda;
© Jerry Small


Here is an image of the yours truly in Photoshop, ready to be printed. I suggest using a standard color checker chart, like the one from GretagMacbeth, when you’re testing your profiles.
© Jerry Small


Above is the Photoshop CS3 “Print” dialog. All of the color management gets handled in the right hand panel of this box. Always remember to turn off color management in your printer’s software or you’ll get unexpected results.
© Jerry Small



Since the inception of digital imaging, no single activity has caused more confusion and frustration than the quest for attaining accurate output. Over the years, professionals and service bureaus have come up with many different concepts of how to produce accurate output. In most cases, it was hit and miss, and in many instances even the most successful results were very limited.

Anyone who works with digitally produced images desires to have a WYSIWYG workflow. In other words, they want their output to look exactly the way it does on their monitors. While it's understandable to feel that way, it's important to understand some of the misconceptions and pitfalls that come with achieving this goal.

The most important thing to understand is, no matter how hard you try, you will never get printed output to exactly match your monitor. But before you start thinking you're totally wasting your time, let me explain why. Put simply, when you view images on a monitor, you're looking at images that are lit by transmitting light through them from behind. When you look at printed images, you are looking at them reflectively. They are produced differently, and therefore they can never look exactly alike. You can get them close, sometimes really close. But they'll never be an exact match. Why? Well, for one thing, images produced by a monitor have a different color gamut (number of available colors) than images printed on paper. Some colors you see on a monitor, especially vivid bright colors, just can't be reproduced on paper. And when that happens, those colors have to be substituted when the image is printed, which forces the image to look different than it does on the monitor.

So Rule #1 in color management is: we are not trying to match our monitors. We are trying to come really close, while at the same time trying to be able to accurately reproduce those same results over and over again. Ideally, we want a situation where we have consistent, predictable color every time we output an image, no matter what it is printed on.

Color management is a workflow that allows us to achieve consistent, predictable color across multiple platforms and multiple devices. For this to work, we have to accept the fact that we'll never match our output to our monitor. Our goal is to come really, really close, but most important, be consistent. In other words, by using proper color management, I can predict from looking at the image on my monitor how it will look when it's printed. It may not match my monitor, and if it's off a little, it will always be off by the same amount every time. For example, if I print a portrait from my computer onto an Epson 7800 using Epson Lustre paper, and it appears a little yellower on the print than it appears on my monitor, I can trust the fact that everything I print from that printer on that paper will always be that little bit yellower compared to my monitor. I can even take it a step further by creating a Photoshop Action to compensate for the difference and guarantee myself that I'll always get prints I am happy with.

Using ICC Profiles

This is achieved through the use of ICC profiles. A profile is a small file that describes the characteristics of the device it corresponds to. For example, a printer profile describes all the color characteristics of the printer/paper/ink combination it was created from. A monitor profile describes the color characteristics of the monitor being used. The workflow, in basic terms, is to convert the colors of an image from the color space of the monitor to the color space of the output device. We can do this using ICC-aware software, such as Adobe Photoshop, or one of the many software RIPs that drive many high-end printers being used today.

There are several ways we can get ICC profiles to help us manage our output. The easiest is to get pre-existing, or "canned," profiles from printer or paper manufacturers. These are generic profiles that will get you good results, but may not always be accurate. The quality of the profiles depends on the conditions and the method they were created under. They can vary from very accurate to not even close. A more accurate means of getting profiles is to either create a custom profile yourself or have someone create it for you. Just remember, you need a different profile for every paper/ink combination you use. How to create a profile is beyond the scope of this article. For now, we'll concentrate on how to use profiles to get accurate output.

To successfully print using profiles, you need three important ingredients: a monitor profile, a printer profile, and a rendering intent.

Assuming you calibrated your monitor, you already have a monitor profile in place and Photoshop knows where it is. So let's go to the printer dialog and see how we use the other two ingredients. As you can see in the photo at the top of this page, the dialog box is divided into three panels in Photoshop CS3. On the left is a preview image of the file you are printing. The center panel has information about the printer and the image we're printing. I pretty much leave that panel alone, except for checking the "Match Colors" and "Show Bounding Box." The right panel is where everything happens. Here's what to do: At the top of the panel is a drop-down box. Make sure it says "Color Management." Next you'll see two radio buttons. Click the one labeled "Document." On the "Color Handling" drop-down box, change it to "Photoshop manages colors." One very important note is that you must disable color management in the printer dialog-that's the dialog that pops up from the printer driver-otherwise, you will get very unexpected results. Next, the keys to accurate output: On the Printer Profile dialog box, select the profile for the printer/paper/ink combination you're using. Lastly, choose a rendering intent.

Rendering intents

Because ICC profiling is nothing more than a translation from one color space to another, we need a rendering intent to tell the color management software how to make that translation, how to map the colors in the image from one color space to another, and also what to do with out-of-gamut colors (colors that are outside the range of the color space the image is being translated to). It all comes down to what level of accuracy you want to maintain in the relationship between colors.

If you use the Perceptual rendering intent, the software will actually change the color numbers, so those colors will be different from the monitor to the printer. However, it will maintain the relationship between the colors, so the image has the same "feel" when you look at it. If you roll your mouse over the rendering intent in the Photoshop CS3 print dialog box, you'll actually see an explanation appear in the lower right panel of the box for that rendering intent. According to many experts, this intent is often used for photographs with a lot of out-of-gamut colors.

If you use Relative Colorimetric, the software tries to compares the whites in the image to the whites in the destination device and maps the numbers accordingly. This actually preserves more of the original colors than the Perceptual rendering intent. Any colors that are out of gamut are remapped to the closest reproducible color in the destination space. This is considered a more accurate rendering intent.

Absolute Colorimetric is a little different. Colors that are within the gamut of the destination are left unchanged. Colors that fall outside the gamut are shifted to the closest reproducible color. The big difference is, white points aren't compared, and the relationship between colors is not maintained. This color space is used mostly to simulate other devices, usually for proofing purposes.

Confusing? You bet! What it comes down to is how you want your images to appear. My suggestion is when you use a profile for the first time, do a little experimenting. Print the same image using the different rendering intents and decide which one you like the best. There are many experts who will insist that you use one rendering intent or another in various situations. But when it comes right down to it, as long as you (and your clients) like the results, that's all that matters, right?

So that's color management in a nutshell. It's not as complex or mysterious as it used to be, or as many people think it is. While many labs will handle the color management for you, this should help you if you ever have to do it yourself, or at the least, give you a better understanding of what's going on behind the scenes.

Gary Small of Photographic Creations, Inc. (www.jsmallphoto.com) has been a pro photographer since 1979, and in business with his father, Jerry, for most of that time. He's been working with digital imaging for more than 10 years; he hasn't shot a roll of film in over five years and instructs other photographers in digital imaging, Photoshop, and color management.


   







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