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don't encode alpha when it's all opaque #108

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1. Generate 32-bit input with an alpha plane that's completely opaque.
2. Encode with cwebp.

What is the expected output? What do you see instead?
Output is in extended format (VP8X), will display as black if the alpha is 
interpreted and will carry additional overhead.
Instead the alpha should not be encoded.

Original issue reported on code.google.com by jz...@google.com on 11 Feb 2012 at 2:38

GoogleCodeExporter commented 9 years ago 
commit 437999fb77db5e915da685bbc8b8d9f48d8e77ee
Author: Pascal Massimino <pascal.massimino@gmail.com>
Date:   Mon Jun 4 15:50:05 2012 -0700

    introduce a generic WebPPictureHasTransparency() function

    VP8-lossy will now avoid writing an ALPH chunk if the
    alpha values are trivial.

    + changed DumpPicture() accordingly in cwebp
    + prevented the -d option to be active with lossless
     (DumpPicture wouldn't work).

    Change-Id: I34fdb108a2b6207e93fa6cd00b1d2509a8e1dc4b

Original comment by jz...@google.com on 8 Jun 2012 at 12:34