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In article <FAEBJHPJNNGCAGDNGLNPIEIHEIAA.email@example.com>, gary <firstname.lastname@example.org> writes >Those familiar with audio sampled data systems know that the sample time is >infinitely small. Equating this to imaging, the pixel should not have size, >but rather a sample density. > No. Whilst the audio analogy certainly has a very short sample acquisition period, the signal is band limited by the pre-filter - which has the same effect as convolving the time domain waveform with an aperture of a specific shape and size. (multiplication in frequency space corresponds to convolution in time). The finite aperture of the pixel or spot performs a similar presampling filter function in image sampling, and the shape and size determine the exact spatial bandwidth that is samples. >Going back to the audio analogy, if you take the sample impulses and play >them back on a DAC making staircase waveforms, the high frequency response >will be incorrect. The nature of the staircase implies a sinc filter was >used, so the playback must incorporate an inverse sinc filter. Since the >image sampling is not infinitely small, I wonder if the use of an unsharp >mask is analogous to the inverse sinc filter. > No - an unsharp mask has a completely different spatial frequency response from a sinc or inverse sinc, so it isn't doing anything similar to it. Remember that in order to see (or hear) the staircase in audio you must examine the waveform in sufficient detail to see individual samples as they are converted by the DAC. In imaging, this is the same as seeing teh individual pixelation. So the equivalent of filtering the transition between filters is to resize the image with pixel replication and then apply an inverse sinc filter of the appropriate size. As it turns out, for zoom ratios up to around 2-3x, this is closely approximated by bicubic interpolation, not unsharp masking. Also remember that when viewing at normal size, the CRT spot or LCD pixels perform a similar spatial filter on the final image. -- Kennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers - Turn off HTML mail features. Keep quoted material short. Use accurate subject lines. http://www.leben.com/lists for list instructions.