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.
_ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada
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