POV-Ray : Newsgroups : povray.beta-test : v3.8 beta 2. Bug with image_pattern use_index keyword. : Re: v3.8 beta 2. Bug with image_pattern use_index keyword. Server Time
29 May 2024 12:07:29 EDT (-0400)
  Re: v3.8 beta 2. Bug with image_pattern use_index keyword.  
From: Kenneth
Date: 15 Mar 2023 09:05:00
Message: <web.6411c13876ee363a9b4924336e066e29@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

> Aside 2: In a surprise to me, the use_alpha option uses the red channel
> when it cannot find an actual alpha channel for the return values.

Confirmed in Windows v3.8.0 beta 1-- using a typical .png COLOR image_map for
the image_pattern (non-indexed and with no alpha-channel). BTW, I already had an
image_pattern test scene available from 2018, courtesy of a Thomas De Groot
post... but I never noticed this red-channel-only behavior.

It seems to me that it should use the image's gray values instead (like a .gray
equivalent). That would make more sense... and would be consistent with, for
example, a bump_map (which uses the gray values for its normals by default).

The other inconsistency is the height_field-- which again uses only the red
channel from a color image_map. That should use gray as well, IMHO.

I wonder why these features are restricted to the red channel? Perhaps, when
they were first introduced, the idea was that only gray-scale image_maps would
be used in them(?)

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