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Evaluating digital color

November 1st, 2007 / By: / Graphics

Advances in technology shifted the responsibility for high-quality color reproduction from printers to graphic designers, photographers, and prepress operators. Part of consistent color reproduction is objectively determining what colors you are actually reproducing.

Any staff member directly involved in creating the color workflow can learn the skills. Start the learning process by selecting a color target file. The target needs to include both continuous tone images, 1-inch-by-1-inch colors, and a gray scale. Then practice measuring, observing, and interpreting digital color values. Digital color values define hue (color family), brightness (total light reflectance), and saturation (chroma). Print drivers and RIP software interpret the CMYK percentages needed to replicate RGB monitor tones differently, and the human eye can see more than CMYK printing can produce.

Open your color target file and the “Information Palette” in your software. Use the eyedropper tool to sample hues and tones of the color target. Observe the CMYK and Lab values. Next, change the CMYK percentages by 10, 20, and 40 percent. Observe each of the created changes in the monitor and printed images. Interpreting the results is more complex and is similar to learning a new language.

Collect target data by selecting one, two, or three colors from the original values before any adjustments. You may select more than one color for each printed target; however, make only one adjustment at a time, regardless of the time pressures. The purpose, at this point, is to observe how the image and values change when changing only one percentage of one of the color channels (CMYK), not to get a perfect image. Measure the whiteness of the specific substrate as you are recording the color values.

Print the original and adjusted targets. Permit the inks to dry before recording any measurements. Set your spectrophotometer according to the instrument manual. Measure the white and your original color values as the reference. Your new color values will be the samples. Use the average of three readings and record it. There will be variations as the fabric surface and ink saturation varies.

Once your digital color values are set and recorded, you are one until you change one of the contributing parts (inks, printers, substrates). The process is an investment in time and effort but is not as costly as an unsatisfied customer.

Jean Dilworth is a professor at Eastern Illinois University teaching textile print and apparel design, and visual merchandising that includes interior and external signage.

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