Photoshop color management tutorial.

Working with Photoshop's RGB and CMYK color space.


Adobe Photoshop CS-CS5 Painting Tutorials

Photoshop Paths | Airbrush Tool | Basic Painting | Layer Masks | Color Management

All Tutorial Text & Images - Copyright © 2011 KHI, Inc.

Before you begin any of the Photoshop tutorials on painting or airbrushing it is important to have a cursory understanding of color theory. If your work is going to be printed, you should be working exclusively in CMYK and not in RGB. Although there may be many good reasons to work in RGB (web graphics only, smaller file size, etc.), for our purposes, CMYK (A.K.A. Subtractive Color) is a better choice.

Additive vs Subtractive Color: The diagram above illustrates the difference between Additive Color (RGB) Fig. 1, and Subtractive Color (CMYK) Fig. 2. Notice that when you combine Red, Green, and Blue in the Additive Color process, the combination produces white. In the Additive Color process, white is the combination of all colors. In the Subtractive Color (CMYK) process, when you combine Yellow, Cyan, and Magenta (CMY), the combination produces black. In the Subtractive Color process, black is the combination of all colors.

Photoshop CMYK vs RGB Color Space

Setting the color space for an image file is done through the Image>Mode setting, with a select of Bitmap (B&W), Index (256 or less, color GIF), Grayscale, RGB (3 color), CMYK (four color), Lab Color and Multichannel. Once you have selected the color space you can make adjustments to a given color by going to Photoshop's "Color Picker" (above) which will show you the ratio and percentages of each color channel.

Munsell Color System

The evaluation of color had no generally accepted system for quantifying a specific color and its color quality before the 1900's. An American painter and art instructor named Albert H. Munsell was the first to identify three basic qualities of a specific color - its hue, saturation and tone. Albert Munsell authored two books on the subject: "A Color Notation" (1905) and the "Atlas of the Munsell Color System" (1915), and hue, tone and saturation are now commonly used everyday terms in color theory and color management.

Color Space for Print

For the Additive Color (RGB) process to work, you need a light source (sun light, computer monitor, etc.). In printing, as it is in illustration, you already start out with white (the surface of the paper, art board, a blank digital file). CMYK is the color space that is used in the 4 Color printing process and the one that you should use if your work is ultimately going to be printed. Additionally, it is helpful to have a 100% pure black channel (black ink only) because we will be using that channel exclusively for our line art.

If your color file contains black-and-white line art you will not want any of the lines to print in all four ink colors because with even the slightest error in registration, it will become too thick and lose its sharpness. Make sure that the line work prints only in the Black color channel of your CMYK file.

Hexadecimal Color Space for Web Graphics

As well as being able to select between RGB and CMYK, Photoshop's Color Picker window allows you to select a palette that is specifically designed for the web using the "Hexadecimal" color formulas. You can also manually enter CMYK percentages and RGB values and your selection will be displayed in the "Select Foreground Color" viewing box.

If you are selecting web colors using Photoshop's color picker you can check the "Only Web Colors" checkbox so that the picker will only show choices in the "web safe" color range of the hexadecimal system.

Gamut Warning and Data Loss by Changing Color Space

With older versions of Photoshop there was significant data loss (color loss) when switching between color spaces, and when converting from RGB to CMYK there were highly unpredictable alterations in the overall color, richness and tonal range of the image due to compression of "out-of-gamut" colors. When selecting a color in the Color Picker" you will see a warning triangle saying: "Warning: out of gamut for printing" which indicates that a 4-color printing press will not be able to replicate this color intensity.

Photoshop Warning Out of Gamut for Printing

Newer versions of Photoshop such as CS5 are far better at making the conversion without dramatically altering the overall look of the image, yet there is still some data loss when converting from RGB to CMYK. More importantly, reverting back to RGB will not restore the original tonal dynamic range of the file. If you are converting a final file it is a good idea to keep a backup copy in the original color space.

If you are working on a file that has already been converted to the CMYK color space Photoshop will automatically prevent you from selecting, sampling or using colors that are out-of-gamut. Note: The following hardware and software was used in this tutorial: An Apple Mac Pro desktop computer, a Wacom Intuos 6x8 drawing tablet, Adobe Photoshop CS-CS5 photo editing software and a properly calibrated monitor.

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