Stephen Withers
Wednesday, 02 April 2008 02:36
Opinion and Analysis
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A few days after we learned that Apple had settled a court case over the MacBook and MacBook Pro displays, news comes of another plaintiff making a similar allegation about the 20in iMac.
Texas resident Chandra Sanders is suing Apple in the US District Court in San Jose, claiming that the company engaged in deceptive marketing by overstating the capabilities of the desktop computer's display.
The 24in iMac uses a high quality display capable of displaying 24-bit colour. Each pixel is made up of three subpixels, each with the ability to show 256 levels of red, green or blue. That's eight bits each. 256 to the power of three is rather more than 16 million, hence the term "millions of colors".
However, the 20in uses a lesser panel that only uses six bits per subpixel, or 64 levels. 64 to the power of three is 262,144 - well short of "millions". Apple (and other manufacturers, it should be noted) turns 18-bit colour into 24-bit colour by rapidly varying the shade of a specific pixel. This process is called temporal dithering.
When you watch TV or a movie, the picture doesn't really move. What happens is that a series of slightly changing still images is interpreted by the brain as movement. Temporal dithering is much the same in that both rely on the way the brain interprets what the eye actually sees.
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