Color Management 101

Introduction to Color Management

Using color management is a critical aspect of taking your digital photos from capture to print. Color management describes an integrated system of computer hardware and software working together to translate color from one device to another in a controlled way. If you want your prints to look their best you should establish and follow a color-managed workflow.

Gamut = Range of Colors Available
Different devices (monitors, printers etc.) interpret color numbers in different ways, because of differences in the type of device and their primaries (their main colors: red/green/blue, or cyan/magenta/yellow/black etc.) No device can reproduce all colors and all devices reproduce color differently. The range of colors that a device can reproduce (or that a digital file contains) is called the color gamut. A large gamut contains many possible colors and a small gamut has relatively few colors available.

Enter the CMS
The Color Management System (CMS) on your computer controls how colors are translated from one device to another. The CMS on Mac is ColorSync; on Windows it’s ICM. Both handle color management automatically at the system level. However, different programs, such as Photoshop, can be set to take advantage of color management or not, and some programs, including most web browsers, do not use color management at all.

ICC Profiles – Source and Destination
The CMS translates color from device-to-device using profiles, also referred to as ICC profiles. A profile describes the color gamut of a device or an image file. Profiles are stored in specific places within your operating system so they are made available to any program using the CMS. The CMS processes the source color values through the numbers in the profile to create the optimum values for the destination. For example, an image file in the Adobe RGB color space would be the source and an Epson printer would be the destination.

Rendering Intents
Out-of-gamut colors are color values present in the source but that do not exist in the destination. For example, the limited gamuts of many color printers pose difficulty reproducing bright shades of blue. The method the CMS uses to handle colors that are out-of-gamut for the destination is Rendering Intent. The two most useful types of rendering intents are Perceptual and Relative Colorimetric: Perceptual compresses the gamut of the source to fit into the destination, remapping all the colors to preserve their visual appearance as perceived by the human eye. Relative Colorimetric keeps all the in-gamut colors unchanged and clips the out-of-gamut colors to the closest possible match within the destination gamut. Perceptual often gives the most natural rendering, but Relative Colorimetric is numerically more accurate.

Calibrate and Profile Your Display
The most important consideration in managing the color in your workflow is to have your monitor calibrated and profiled. You need to use the correct monitor profile to see accurate color. Most monitors come with a default profile; you can either use the profile provided by the manufacturers or make custom profiles yourself using specialized hardware and software such as the X-Rite i1 Display system.

Embed Profiles in Image Files
A color space defines the available gamut for an image file or device. In Photoshop, this is referred to as the file’s Working Space. The most common working spaces are sRGB, Adobe RGB (1998) and ProPhoto. An image file can have an embedded profile that defines the working color space and tells the CMS how to interpret the colors for that image.

When you save image files, most often you should embed the working profile so that later in the workflow all the devices know the working color space and handle the color translations appropriately. (Note that if you choose “Don’t Color Manage This Document” from the warning dialog box in Photoshop, you are disabling color management for that file during that working session, producing unpredictable results – not recommended.)

When sending an image to a lab or other vendor, you need to know how your file will be processed. Ask them if there is a specific color space that they want the file saved in. In some cases you may be asked by a service provider to not embed the profile. In these cases, you can still convert the colors in the image to another color space, which will often produce the same results as if the profile was embedded

Find out if the vendor can provide a profile for the printer they will be using; if you have one, you can Soft-Proof the file in Photoshop.

Soft-Proofing
In Photoshop, you can use printer profiles to simulate on your monitor how the image will appear when printed. This is called Soft-Proofing. It’s important to understand that because a monitor is a transmissive device (transmitting light to generate color on the screen) and a print is a reflective image (made visible by light reflecting from the surface of the paper and ink) that it is physically impossible to have a print look exactly like what you see on screen. However, Soft-Proofing provides a reasonable simulation, and with practice, you can train your eye to accurately predict how the print will look.

To Soft-Proof in Photoshop (not available in Elements):

Open your Master file and select Image > Duplicate to open a copy of the image in a second window. Position the two document windows so you can see both images.
In the Master file, select View > Proof Setup > Custom…
In the Customize Proof Condition dialog box, choose your desired printer profile from the “Device To Simulate” dropdown menu.
Make sure Preserve Color Numbers is unchecked.
Simulate Paper Color and Simulate Black Ink should both be checked.
Try both Perceptual and Relative rendering intents to find the best color match between the soft-proofed Master file and the Reference file.
Always enable Black Point Compensation.