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“One of the issues is that color was limited in how bright it could be,” added Domogalla, who is based in Beaverton, Ore. “There are RGB filters between the backlight and screen. Each of them reduces the amount of light getting through. Grayscale can be very bright, which is necessary for challenging x-rays like chest and breast.”
There is one area where grayscale remains the best. “Currently one application we see in the market [that still is] grayscale because it’s the most demanding is mammography, Domogalla says. “The luminescence and resolution are very critical, so they’re not using color. Off-the-shelf color displays are not bright enough to look at grayscale images in a diagnostic way. Not all color displays are bright enough yet.”
Swiderski agrees. “Color will fall short for 5mp (mammography). I don’t see anything at that pixel level for mammography. It needs [many] very fine pixels. The matrix is 2x2. Right now, 3mp color is common.”
Contrast also is vital in disciplines such as mammography. The way the human eye responds to contrasts in light levels is not linear. At low levels, humans can notice small changes in luminance. At higher luminance, the change needs to be much greater before the human eye can perceive the difference from one level to the next.
One way to calibrate is via the DICOM (Digital Imaging and Communications in Medicine, Rosslyn, Va.) curve, which can be plotted to show measured luminance levels versus increments of perceived difference. This sensitivity to changes in contrast was developed by the American Association of Physicists in Medicine (College Park, Md.)