Color Modes for Documents | Real World Adobe Creative Suite 2

This is one of those tricky subjects that manages to trip you up every so often. When you work in Photoshop or Illustrator, each document itself has a color mode. This color mode governs how the colors within the document are defined, and as you might already know, some modes are better than others, depending on your file's particular destination, such as web or print.

Color Modes in Photoshop

Photoshop has eight different color modes. You can change the color mode of a document by choosing Image > Mode.

RGB Color uses three channels of information (Red, Green, and Blue) to define the image. This is the most common color mode for scanned images as well as those taken with digital cameras. ImageReady uses only the RGB mode to work with images, because its documents are primarily intended for web display.
CMYK Color uses four channels of information (Cyan, Magenta, Yellow, and Black) to define the image. This is the most common mode for images that will be printed using process colors. Most RGB files are converted into CMYK before final output.
Lab Color (based on CIE L* a* b*) uses three channels of information to define an image in a way that is device-independent. Device-independent means the that the color definition does not depend on the type of device that it is displayed on. (By contrast, RGB Color and CMYK Color define color in relation to a particular device for example, a particular monitor or printer. An RGB or CMYK color will look different depending on the output device you have chosen. )
Grayscale is a single-channel color mode that contains 256 shades of gray to display an image. Convert images into this color mode for black-and-white printing.
Duotone is a single-channel color mode that allows you to specify up to four plates for process or spot colors. These plates mix together in the final image. The information for these colors does not add to the file size; rather, it is contained in specialized duotone curves.
Indexed Color is a single-channel color mode that uses 256 colors to create an image. These images are rarely used in commercial printing, but can be easily converted into web graphics.
Bitmap is a single-channel color mode in which color is either on (black) or not on (white). Images in Bitmap mode are often called 1-bit images because they are defined only in terms of the one color. Steve wishes that Adobe had come up with a better name for this mode because Bitmap mode images are often confused with bitmapped images, which include all scanned or raster images. (See Chapter 4, "Pixels and Raster Formats.")
Multichannel is a specialized mode that takes the channels in any of the other color modes and breaks them out into individual channels unlinked to any color description. You can also convert duotones to multichannel images to examine the appearance of each color in the duotone.

However, it is important to understand that if you have a document defined as RGB Color, then any colors defined using CMYK values may shift when the document is converted from RGB to CMYK mode. (See "Color Management" earlier in this chapter.)

Tip: Don't Convert Back and Forth

It's not a good idea to repeatedly convert an image back and forth between RGB and CMYK modes. There is some loss of image quality every time you make this conversion.

Choosing the Right Mode in Photoshop

What is the best color mode in which to work? If your document is going to be printed using process colors, then the document will eventually be converted from RGB to CMYK. However, most people work in RGB color mode. This is because many of the Photoshop filters are not available in CMYK mode. All the filters are available if the document is in RGB mode.

An even better reason to work in RGB is that most of the images we work on come from digital cameras and scanners, which use RGB. Working in RGB means that your files are smaller (three channels instead of four). Furthermore, RGB has a larger color gamut than CMYK.

This is why most artists and designers prefer to keep a document in RGB color mode as long as possible before converting to CMYK.

Color Modes in Illustrator

Illustrator has only two color modes, RGB and CMYK. You can change from one color mode to another by choosing File > Document Color Mode. Most artists and designers get in the habit of working in the CMYK mode in Illustrator. This ensures that their colors don't shift when converting their print documents from RGB to CMYK. Of course, if you're creating a web document, you should usually work in RGB mode.

However, like Photoshop, the Photoshop filters under the Filter and Effect menus are unavailable when the document is set to CMYK. If you intend to use any of the Photoshop filters that are in Illustrator, you should use the RGB color mode. Then remember to switch back to CMYK if you're sending your document off for print separations.

With only the two color modes in Illustrator, what do you do if you need to output artwork as a one-color (black-and-white) file? Placing CMYK or RGB Illustrator files into InDesign will create extra plates that are not desirable. Because of this, Sandee has spent many unhappy hours manually selecting colors and converting them to tints of black.

Fortunately, our good friend Mordy Golding, author of Real World Adobe Illustrator CS2, gave us a great technique for converting color Illustrator files into grayscale art. This is a perfect example of using the Creative Suite applications together to solve a problem:

Place the Illustrator file into InDesign.
Use the Adobe PDF 7.0 printer driver to convert the file to PDF.
In the Output section of the Print dialog box, set the Color setting to Composite Gray.
Open the converted PDF file in Illustrator. The colors are converted into grayscale tints of black.

Not all Illustrator elements will make it through this process. Blends are converted to discrete art. Gradient mesh objects are converted to images. Brushes, symbols, and appearances are expanded into discrete elements. Patterns are converted to grayscale, but are not listed in the Swatches palette. However, Sandee finds this a terrific solution for converting basic art shapes from their color settings into ordinary paths that she can then use for further artwork.

Color Modes in InDesign

Compared to Photoshop and Illustrator, the colors in InDesign documents are complete anarchy. Colors can be defined as CMYK, RGB, or Lab. Placed images can be defined as CMYK, RGB, grayscale, or even Indexed Color. There are no color modes governing the documents.

The colors in InDesign are converted according to the final output. If that is CMYK separations or composite printing, then the colors are converted accordingly. (See "Printing in InDesign" in Chapter 16, "Preflighting and Printing," for information on InDesign's output settings.)

InDesign does have settings for the transparency blend space. This is the color space that InDesign uses when displaying and flattening objects that have some form of transparency applied. (See Chapter 11, "Transparency," for a list of which features apply transparency to pages.)

The transparency blend space can be set to CMYK or RGB. Choose Edit > Transparency Blend Space. If you are creating work for process-color separations or composite printing, choose CMYK as the blend space. If you are creating work for screen or web, choose RGB. (Illustrator always uses the transparency blend space that matches the document color mode.)

Color Modes in Acrobat

Acrobat also has no specific color mode for its documents. Whatever the settings were when the document was created is how the colors appear in the PDF file. This can create some rather chaotic documents where images are in both RGB and CMYK while text is in grayscale. Like in InDesign, the colors in a PDF document can be converted at print time. In Acrobat, the settings for converting your color mode are in the Advanced Print Setup dialog box on the Output panel. (The Color Profile setting on this panel also sets the transparency blend space.)

Acrobat 7.0 Professional allows you to convert objects in the document from one color mode to another. Choose Tools > Print Production > Convert Colors. This opens the Convert Colors dialog box, where you can choose which types of colors in the document to convert.

Color Modes in GoLive

There are no color modes for GoLive documents. As an application that creates web pages, all colors are RGB. However, you can place images from any of the Creative Suite applications into GoLive layouts. Any CMYK colors are converted into an RGB format.