RE: Image resample effect on color
RE: Image resample effect on color
- Subject: RE: Image resample effect on color
- From: "michael shaffer" <email@hidden>
- Date: Wed, 15 Oct 2003 09:53:41 -0230
Douglas asks ...
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...
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When resizing an image in Photoshop, what effect do the
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different resample image modes (Nearest Neighbor, Bicubic &
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bilinear) have on an images color, if any?
Graeme writes ...>
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...
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If there are sharp edges or transitions in the image, then the
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colorspace can affect the result. The most noticeable area this appears
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in is anti-aliasing of feature edges. The most accurate results will
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be obtained when the resampling is performed in a "linear light"
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colorspace.
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An RGB space with a gamma of 1.0 is such a space, as is XYZ space. You
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would need to watch your precision in such spaces (you need more than 8
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bits for any sort of quality).
Although the side-effects are excerbated by contrast, I would describe
what happens differently. I believe you can disregard all parameters of
color space other than 'gamma', and imagine 2 neighboring pixels on the
color space appropriate gamma curve. A resulting interpolated pixel will
not be on the curve, but rather on a straight line drawn between the 2
pixels. Now, I believe you can understand why contrasting pixels will
result in a calculated pixel much futher than the gamma curve ... and a
worse case scenario being 'black' averaged with 'white' resulting in '128'
rather than an (e.g., gamma=2.2) value of '183'.
With regard to which interpolation method, I think you can now see that if
one method involves more pixles than another, the calculation is less likely
to involve contrasty pixels (... but still is no guarantee). Many,
including myself, have complained of this, but no one has claimed to see any
significan difference (including me).
cheerios ... shAf :o)
Avalon Peninsula, Newfoundland
www.micro-investigations.com
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