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Monday, January 7, 2008

Hi-Tech Studio: Complete Color Calibration

Color management from reality to reproduction


This Article Features Photo Zoom


There's no question that maintaining consistent color across your workflow, from capture to delivery to a client or making a print, is critical. Using the latest tools like the X-Rite i1 Display 2 (above) and the Datacolor Spyder3PRO keeps your system within the necessary tolerances.
Plato said that art is thrice removed from reality.
Although the philosopher wasn't a photographer, he hit the nail right on the head where digital imaging is concerned. If we follow what happens to the color of an object during the photographic process—from capture through output—we see several junctures where the colors are likely to be changed unintentionally, and we can gain a better understanding of why it's important to use calibrated devices.

Take a yellow daisy growing in a sunlit field, for example. We use a camera to capture a digital image and our brain to record a memory of the color. Scientists believe that no two people see colors exactly alike, so from the very beginning our “art” becomes separated from reality. Human perception is heavily influenced by physiological and psychological factors. Long story told short, attempting to accurately judge colors simply by looking at them is futile.

All digital cameras render colors slightly differently, too. This happens because all digital signal-processing engines—the computer “brains” inside cameras—have specific color biases. Shooting RAW format is a step in the right direction, but doesn't solve the problem completely because differences in lens coating and construction influence color rendition. In some cases, these variations are slight, but in certain situations they can be enormous. In every case, the original color can be restored on the computer—and that's where it starts to get complicated.

There are ways to objectively measure color, but few photographers do this. Instead, they rely on experience and personal taste when adjusting the colors in the digital image to match the original hue, chroma and lightness of the colors in the object. That's all part of the creative process. However, even the sharpest eyes in the world can't accurately evaluate color unless it's being viewed on a computer monitor that has been calibrated. And if it's accurate color prints you're after, your printer must be calibrated as well.

Digital cameras, computer monitors and color printers each use specific color spaces. Color space describes a range, or gamut, of colors. All digital cameras can capture images in standard RGB color space. Some cameras offer Adobe RGB (1998) as an alternative. Standard RGB, or sRGB, was defined by Microsoft and HP and popularized as a standard to assure that colors would appear approximately correct when viewed on a typical computer monitor. Adobe RGB was introduced to include the colors that can be printed using CMYK inks—even though it uses only the three primary colors. This is important when images are printed on commercial presses.

color calibration Unless the color spaces are correctly mapped from device to device, the colors won't match. Even if you're using the published color profiles for your LCD monitor and inkjet printer, you can't expect to produce consistent, predictable results unless both have been calibrated. Calibration produces ICC color profiles that communicate how colors should be mapped from the color space of the input device to the color space of the output device. The critical starting point is the map that specifies how the colors should be reproduced on your color monitor. But if your monitor isn't calibrated, you won't be able to see an accurate rendition of the colors, even if the software is correctly translating one device's profile to another. Consequently, once again, it's impossible to make adjustments that are meaningful or reliable on an uncalibrated monitor.

To achieve complete color calibration, you need the right tools. A typical configuration consists of one piece of hardware—a colorimeter—and a software suite. A colorimeter is a sensitive, high-precision light meter that resembles a high-tech hockey puck. It's powered by a cable that connects to your computer via a USB port. The cable drapes over the back of your monitor and the colorimeter hangs suspended on the monitor's face like a rappelling mountain climber. There's a counterweight that allows you to hold it securely in a stationary position so that it can analyze your monitor output with absolute objectivity. The software provides the tools you need to tweak the colors until they zero in on the standard values. Additional applications enable printer calibration.


 

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