Updated 7/12/05
 

Inside WI > Biocomputing > Graphics > Photoshop > Color Management

 

Color Management

Color Settings

If color settings are set properly from the beginning, they can improve color consistency between scanner and monitors, between different monitors, and between monitors and printers. If they are set incorrectly, they can cause irreversible damage to your image.

When you run Photoshop for the first time, it will ask you to set your color settings. Please go to
Edit > Color Settings and set them like this:

The next step is to calibrate your monitor. Otherwise you may not see the advantages of this sophisticated system. It takes only 5 minutes.

 

What is Color Management? ............Back to top

Each device we work with produces a slightly different range of color. Color Management tries to keep files from different devices looking consistent as the file moves from scanner, to monitor, to another monitor, to printer.

Although Adobe's color management does a good job, it can't solve the problem entirely. Some of the visual differences have to do with the difference between making a color with light vs. making the same color with ink. The ingredients going into the color are much different with light than with ink. The two colors are made in 2 different color spaces. You can think of a color space as a kitchen with limited ingredients. Color Management is all about trying to make these different recipes come out with the same result.

RGB vs. CMYK .............Back to top

RGB and CMYK are two different color spaces. The RGB color space uses light in colors of red, green, and blue to create the visible spectrum. Our eyes see color in terms of reflected light, so in a way, the real world is in RGB. That is why RGB devices that use light to create color, such as film recorders, scanners, and cameras can reproduce color fairly accurately.

However, as soon as we try to take the image created by light and put it on paper, we enter the realm of
CMYK. Cyan, magenta, yellow and black are the colors of ink we use to try to reproduce the colors we see in nature. No matter which printer you use, you are going to need ink, dye, toner, or some physical manifestation of these colors. The ingredients used in the recipe limit accuracy in the creation of a color, so there will always be a difference between what you see on your monitor and what prints out.

RGB. Three colors of light, red, green and blue make white light. (Also make cyan, magenta and yellow).
CMYK. Three inks, cyan, magenta and yellow make black. In practice this black is sometimes muddy-looking, so a separate black, K is usually added. (red, green and blue are also made)

Gamut .............Back to top

The total range of colors able to be produced by a device is called its gamut. The explanation above is usually summarized by saying that the RGB gamut is larger than the CMYK gamut. Gamut applies to device capabilities, but can also be applied to other components of the reproduction process. For example, a given printer can reproduce a wider range of colors on coated paper than it can on newsprint. Therefore, coated paper is said to have a wider gamut than newsprint.

Within RGB and CMYK spaces, more variations in gamut exist. Monitors, for example, have a much smaller gamut than slide film and high quality digital cameras, which in turn have a much smaller gamut than what the human eye can perceive. Between monitors, there are also differences in gamut dependent on the phosphors and other hardware components used. Gamuts of printers also vary so that even though they follow the same color recipe, they often output slightly (or greatly) different results. Because of all this, color is highly device-dependent.

Early Color Management .............Back to top

In view of the above, converting color from RGB to CMYK with much accuracy and consistency as possible has been the focus of the printing industry. Photoshop, as a major component of the printing process, has had to address the issue as well. In previous versions of Photoshop, the RGB values were always defined as those displayed by your monitor.

This was simpler, but the RGB values in an image were "clipped" to the the gamut of the monitor, which, as mentioned above, has a much smaller gamut than film. Specifically, the monitors clip some of the cyan values that actually can be printed in CMYK, resulting in a smaller printing gamut than necessary. Also, because monitors vary so widely in their behavior, images looked different on each new machine. They also printed differently on each different printer. It was very difficult to predict what an image would look like when printed.

Color Management Systems .............Back to top

A color management system (CMS) is a set of software tools which attempts to compensate for the device dependent nature of color by mapping colors from a large gamut, like a monitor, to the a device with a smaller gamut, like a printer.

ICC

Though there will never be a perfect match between RGB and CMYK output, the International Color Consortium (ICC) has minimized the problem by establishing color standards. An ICC color management system has three components:

1. A device-independent color space (CIE)

2. Device profiles that define the color characteristics of a particular device.

3. A Color Management Module (CMM) that converts color from one space to another using the device profiles.

Current Color Management .............Back to top

Photoshop 5.0 made their workflow ICC compatible by uncoupling the RGB working space from the monitor, and including calibration software (Adobe Gamma) that allows you to create an ICC profile for your monitor.

 

 

By choosing an RGB space wider than that of the monitor, you are more likely to encompass all the colors printable on your printer (blue triangle). Instead of converting to the monitor's space (yellow triangle) and then to the printer, which clips colors from the CMYK space, the CMM uses the monitor's ICC profile, which you create using Adobe Gamma, to map the colors from your working space to the monitor space so you can edit the image. The colors retain their relationships to each other, so what you see is visually similar to the actual colors in your color space. Then when it is time to print, the larger color space, not the monitor space, is converted to CMYK by the CMM, using the profile of the printer you are using. This method is more accurate, and so gives you more control over the colors in your images.

Problems begin when images in one RGB working space are converted to another. Each conversion to a new color space changes the colors. After a few times, the image becomes severely degraded, especially the greens. When computers are set up differently, you may try to open your file on another computer and get the message that there was a profile mismatch. This means that this computer has a different RGB working space than the one on which you created your image. Because at Whitehead we all have many files originating in different places, the best thing to do in this situation is to choose "Don't convert".

 

Now that your images can safely be displayed and saved in Photoshop, you will begin to see the benefits of this new system in terms of color matching. First, you need to take a couple minutes to calibrate your monitor.

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