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Tuesday, January 4, 2011

Color Printing Technique

The leap from computer monitor to printed output is where most professionals experience issues of color shift and a loss of punch in a photograph. Los Angeles-based pro Lee Varis takes us through the steps to get perfect prints.

This Article Features Photo Zoom

After your image is sized and sharpened, it’s ready for you to make a print. To this point, you’ve been working with a backlit display with vivid RGB colors that exceed the saturation and brightness of anything you can put on paper. Now the moment of truth arrives, and you need to translate what you see on the monitor to a print that can convey the same feeling. The problem is much the same as it was when photographers shot transparency film: There’s still a huge discrepancy between the dynamic range and color gamut that can be represented with a glowing backlit monitor image and what can be printed on paper, where the brightest thing is the white paper. Another major issue is the way images are constructed in the two different media. RGB images on the monitor exist in an additive color space: Red, green and blue light is added together to make white. CMYK images, which form the bulk of paper-based output, use cyan, magenta, yellow and black to subtract from paper white to make a color image.

Figure 1

Translating From RGB To CMYK
Typically, all of our corrections and edits are made in RGB, and the majority of printed outputs are in CMYK. This includes desktop inkjet printers that are designed to receive RGB files. These printers internally transform RGB input into some kind of CcMmYKk-type color for the specific ink set that the printer uses. Even true RGB output devices, such as a LightJet printer, don’t actually have a standard RGB workspace color gamut. There-fore, all prints require a color transformation to occur from the workspace (editing color space) to the output (printing color space) for optimum results. All such transformations are handled by the color management system. Photoshop uses ICC (Inter-national Color Consortium) profiles to manage color inside the application. Effective color management requires profiles that describe every device used in the image creation workflow from workspace to monitor to printer. I select default profiles for my RGB workspace and CMYK workspace in Photoshop color settings. Frequently, the default CMYK workspace is used for generic CMYK output. Ideally, the color transformations necessary for printing to a specific printer utilize a profile for that specific device. Fortunately, most of the modern desktop printers provide reasonable profiles that are installed with the device drivers, and we can use these profiles to control the color transforms for printing.

Figure 2

Soft Proofing
Photoshop includes a method for previsualizing the effect that gamut reduction in the output has on the image. You can find this preview, often referred to as a soft proof, under the View menu. Select Proof Colors under the View menu or press Command + Y/Ctrl + Y to toggle the soft proof on or off. This changes the screen to simulate the appearance of the print. The default proof color is Working CMYK; you can select your CMYK color space in Photoshop Color Settings (Figure 1).

You can change the proof colors to match the output you’re going to use. Go to View > Proof Setup > Custom. You’ll get a dialog that allows you to select a profile for a printer and a rendering intent for your transformation (Figure 2). You can select any output profile you want; you aren’t restricted to working with CMYK or any of the default selections such as Monitor RGB or Windows/Macintosh RGB. If you have a profile for an Epson printer, you can select it here. Select View > Proof Setup to change the output device you want to simulate.

The Simulate check boxes at the bottom of this dialog are particularly interesting. The Simulate options allow you to see a more accurate preview and force an absolute color match to the screen. However, evaluating the color this way requires a little practice. When you select Proof Setup and check the Preview box, you might observe a very slight change in appearance, depending on the color gamut of the original. Normally, you’ll see very little change. When you select Ink Black, the preview changes to reflect the actual intensity of the black ink on the paper to be printed. This can make the image seem a little dull, but it still isn’t entirely accurate. To be accurate, you need to select Paper White. This often results in a very dull rendition—yuck (Figure 3)!