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FAQs about Canvas 5 color management

This FAQ discusses how Canvas 5 converts and displays colors, and how Canvas compensates for differences in monitors and printers to reproduce colors as accurately as possible. The information here includes some basic color theory you might find useful when preparing documents for color output.

Q: How does Canvas perform color conversions, and how can you calibrate Canvas to accurately convert and display colors?

A: To understand how Canvas 5 deals with colors in your document, you need to know:

  • the difference between device-dependent and device-independent color spaces
  • the properties of the three main color models used in computer graphics: RGB, CMYK, and LAB (also known as CIELAB).

Device-dependent color spaces, such as RGB and CMYK, appear slightly different on every output device. For example, monitors are RGB devices; each monitor uses different phosphor shapes, arrangements, or mixtures, and responds to the same RGB values with sometimes astonishingly different results. Therefore, the same image on two different monitors won't look exactly the same, even if the brand and model are identical.

In contrast, LAB color is a purely mathematical construction that is completely independent from output devices; in fact, there is no such thing as a LAB output device. Unlike RGB and CMYK, which are greatly affected by the physical properties of an output device (phosphor brightness, ink amount, and so on), LAB colors have no direct physical correlation. The LAB color space defines colors using a luminance value and two color components, ranging from red to green and yellow to blue. Using these three components, LAB defines colors so that two devices will interpret a LAB color exactly the same way.

For this reason, Canvas 5 uses LAB color space as a "hub" for performing color conversions. For example, when converting an RGB image to CMYK, Canvas first converts the image to LAB, then to CMYK. This has the effect of "normalizing" the color data; even though devices must eventually convert the LAB colors to RGB or CMYK for display or printing, at least the original data conform to a universal standard, unaffected by the physical properties of a specific monitor or printer.

Canvas also lets you specify certain important information about a monitor or printing press to make conversions between color spaces more accurate. The Calibration submenu commands (Monitor Setup, Printing Inks, and Color Separations) in the Edit menu tell Canvas how to compensate for your particular system when converting from LAB color mode. For example, you can use the Monitor Setup command to tell Canvas what type of phosphors your monitor uses, and Canvas will adjust the onscreen RGB colors to compensate. Similarly, the Printing Inks dialog box lets you compensate for different types of inks, paper, press, and other aspects of the printing process. (In general, this type of calibration is necessary for professional printing jobs only.) Canvas uses the Printing Inks information when converting colors between CMYK and LAB, and when creating CMYK separations from LAB color data.

Q: How does Canvas simulate CMYK colors on RGB monitors? A: Because monitors are RGB devices and colors used in commercial printing are CMYK, Canvas does some color conversion to provide you with an RGB approximation of CMYK colors onscreen so you can get an idea how the final product will look. Canvas converts CMYK values to LAB using the Printing Inks dialog box settings and a proprietary formula, called the ink recipe. Using the Monitor Setup settings and a standard formula, Canvas then converts the LAB values to RGB for display. This process is also referred to as "soft proofing," because it lets you preview CMYK colors without printing.
Q: How does Canvas convert RGB colors to CMYK? How does "black generation" affect this process?

A: To convert RGB colors to CMYK, Canvas reverses the previous procedure, converting RGB to LAB (using Monitor Setup settings), then LAB to CMYK (using Printing Inks settings). In addition, Canvas uses settings in the Color Separations dialog box to determine how much black ink to use in generating CMYK colors. In theory, 100 percent cyan, magenta, and yellow results in black; however, in practice, these three inks can't produce real black or dark tones. To produce darker colors, you need to add black, and reduce the amount of cyan, magenta, and yellow.

The amount of black you should use depends on the content of a document. In general, you should use less black for high-contrast images with a variety of colors, and use more black for text, line drawings, and images, where the colors are less intricate and darker shades are required.

To determine what ratio of black to color inks to use when separating colors, Canvas uses the Black Generation settings in the Color Separations dialog box. To open the Color Separations dialog box, choose Calibration > Color Separations in the Edit menu.

Keep in mind, however, that the onscreen appearance of colors can never reproduce the printed result with complete accuracy. The only way to be sure the colors are correct is to print proofs using the actual negatives for the final product.

Q: What are "separation tables," and how does Canvas use them?

A: Canvas doesn't do the math to convert RGB, LAB, and CMYK color modes on the fly; that would be agonizingly slow! Instead, Canvas builds three separation tables that it uses for screen redraws and color conversions:

  • The CMYK to LAB table is based on changes in the Printing Inks dialog box settings.
  • The LAB to CMYK table is based on changes in the Printing Inks or Color Separations dialog box settings.
  • The out-of-gamut table tracks which colors cannot be reproduced using CMYK. Canvas recalculates this table whenever the LAB to CMYK table changes.

Some vendors provide separation tables with output devices and color conversion software. The Calibration > Separation Tables command in the Edit menu lets you save and load Adobe Photoshop-compatible separation tables, so you can get the best performance from these devices and software products.

Q: Does Canvas support ColorSync? A: Canvas does not currently support ColorSync, an Apple Computer system for color matching. The Canvas ink recipe is specifically optimized to produce good results for color offset printing, inkjet printing, and dye sublimination printing.
Q: Why does Canvas define HSL colors with RGB values? A: The HSL color system is based on hue, saturation, and lightness values. Canvas provides the HSL system as an alternative to viewing and defining colors with CMYK or RGB values only. However, unlike CMYK and RGB colors, HSL colors cannot be outputted. For this reason, Canvas defines HSL colors with RGB values.



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