On Sat, 22 Dec 2007, hard off wrote:
hi andrew. would love to see some patches that demonstrate what you're talking about, it's all a bit over my head.
Try to zoom into a part of a GEM image that is in the YUV colourspace or that formerly was (e.g. digitising a TV signal or taking input from most webcams). If the image is as sharp as it can be tuned to be, you will be able to see that the colouring of the pixels is blurry compared to their intensity. The blur is either horizontal or both horizontal and vertical. For example a pure red diagonal bar over pure green background will usually show some pixels that are a different shade of red or a different shade of green. If it doesn't, it means that you picked two shades that have the same brightness, or that the bar is positioned exactly on colouring pixel boundaries. The different shades appear because the colouring pixels are twice bigger (or more) than the brightness pixels, and the boundary of the bar you are filming is being better represented by brightness than by colour.
About the non-linearity of vision... This is something else, and a good start into that, is to look at gamma correction. Gamma correction is actually correcting the monitor, which doesn't output light proportional to its electric input, and has to be compensated. I mention gamma because the gamma formula is both simple and non-linear, so it's a good starting point about non-linearity, but it doesn't actually address the non-linearity of vision. You could perhaps look at the HSV colour objects that Claude was talking about, and look at how the conversions are made (just some floatboxes and one conversion object). It is a common example of non-linear mapping from RGB, but it should also be noted that it's not linear relative to vision, no matter how superficially it may look like it's closer to one's understanding of colours. Look also at when you crossfade two colours, even if you tune your gamma correctly, how often the average of two colours doesn't feel like it's halfway between the two colours.
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