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> -----Original Message----- > From: firstname.lastname@example.org > [mailto:email@example.com]On Behalf Of Bruce Fraser > Sent: Monday, August 20, 2001 9:50 AM > To: firstname.lastname@example.org > Subject: Re: pixels, bis > > I'd also have to say that the sources that refer to a capture element > in a CCD as a pixel are smoking stuff. It's the exception rather than > the rule for a single capture element to form a single image pixel. > Most CCD scanners use three capture elements to form an image pixel, > and drum scanners form image pixels without using an array of capture > elements. With striped-array cameras, each image pixel is typically > formed from 4 capture elements. Calling a CCD element a pixel > strongly invites the conclusion that there's a one-to-one > relationship between capture elements and image pixels. This ain't a > hill worth dying on, but to my mind doing so invites confusion. All this means is that the pixels from the sensor elements, or from the sample-and-hold on the analog voltage from the phototransistor, are resampled to produce a different set of pixels. I would still say that the capture elements produce pixels, just not the ones you eventually see in your image file. I think it's most useful to regard pixels as point samples. The fact that a scanner or camera pixel physically captures light from a nonzero area simply means that some two-dimensional filtering function has been applied before point samples were taken. Similarly, the fact that a CRT or LCD pixel physically generates light over a nonzero area means that some two-dimensional filtering function is applied to the point samples. The filtering function in a simple CCD or LCD is probably rectangular, while the filtering function of a flying spot scanner or CRT is probably more gaussian, the latter generally producing less aliasing. -- Ciao, Paul D. DeRocco Paul mailto:email@example.com - Turn off HTML mail features. Keep quoted material short. Use accurate subject lines. http://www.leben.com/lists for list instructions.
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