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api.md: mention 'exact' default in WebPEncodeLossless*

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Note that config.exact defaults to 0 and point users to WebPEncode() if
the default isn't acceptable. This duplicates the comment from encode.h
for visibility. Follow up to:
6d2e11ec encode.h: mention 'exact' default in WebPEncodeLossless*

Bug: 449296530
Change-Id: Iba44dbcbb179bd80ea0a6b9e129b2c7e0a406916
This commit is contained in:
James Zern
2025-10-06 13:49:20 -07:00
parent 1f0a494e80
commit 64dce5d826
2 changed files with 10 additions and 3 deletions
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6
doc/api.md
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@@ -36,6 +36,12 @@ size_t WebPEncodeLosslessBGRA(const uint8_t* bgra, int width, int height,
Of course in this case, no quality factor is needed since the compression occurs
without loss of the input values, at the expense of larger output sizes.
Note these functions, like the lossy versions, use the library's default
settings. For lossless this means 'exact' is disabled. RGB values in fully
transparent areas (that is, areas with alpha values equal to `0`) will be
modified to improve compression. To avoid this, use `WebPEncode()` and set
`WebPConfig::exact` to `1`.
### Advanced encoding API
A more advanced API is based on the WebPConfig and WebPPicture structures.

7
src/webp/encode.h
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@@ -65,9 +65,10 @@ WEBP_EXTERN size_t WebPEncodeBGRA(const uint8_t* bgra, int width, int height,
// lossless manner. Files are usually larger than lossy format, but will
// not suffer any compression loss.
// Note these functions, like the lossy versions, use the library's default
// settings. For lossless this means 'exact' is disabled. RGB values in
// transparent areas will be modified to improve compression. To avoid this,
// use WebPEncode() and set WebPConfig::exact to 1.
// settings. For lossless this means 'exact' is disabled. RGB values in fully
// transparent areas (that is, areas with alpha values equal to 0) will be
// modified to improve compression. To avoid this, use WebPEncode() and set
// WebPConfig::exact to 1.
WEBP_EXTERN size_t WebPEncodeLosslessRGB(const uint8_t* rgb, int width,
int height, int stride,
uint8_t** output);