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Fixing Disappearing Texture Alpha Details in MipMaps
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[quote][b]xaos[/b] wrote: Unless you actually read it :-) Just for fun: (33, -54, 164, 164, -54, 33)/256 gives apparently a relatively well-behaved 1d filter (some ringing of course, the truncation not helping, but preserves detail pretty well). It needs clamping of course (and will overshoot somewhat for small transients, but max kind of does that as well)... Btw. another problem with max is (at least when alpha is premultiplied, which it often is) that mip-levels will tend to become progressively darker when using it solely for alpha. Compensating for that is somewhat cumbersome; I think to stay true to your scheme you would have to basically sort the 4 pixels (or find the one with maximum opacity at least), then blend both color and alpha of the average with the maximum. This then will shift the problem to textures which are inverted forms (so small holes instead of small non-holes), as these would likely become completely opaque in mipmapping (or at least much more opaque than they should be, this is kind of what happens at the mip-level boundary further away). If building the mipmaps offline it might be worthy to take gamma correction into account (at least usually a value of 128 does not correspond to a real luminance of 0.5, but rather somewhere around 0.75), and use a larger filtering kernel. I would expect your empirical formula to achieve a similar effect in certain cases more by accident, as the problems kind of cancel each other. (Yet another approach would be stochastic sampling maybe, in particular together with alpha-testing, and ideally generating all mip-levels from the source image directly then, with larger and larger sampling areas. You might also check out blue noise and green noise dithering which are roughly related.)[/quote]
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