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doc(imgcodecs): update 16-bit support and opaque alpha channel behavior for AVIF

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Kumataro
2026-10-26 19:09:42 +09:00
parent 2b7cd24889
commit ba021a17a8
1 changed files with 3 additions and 2 deletions
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modules/imgcodecs/include/opencv2/imgcodecs.hpp
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@@ -556,10 +556,11 @@ can be saved using this function, with these exceptions:
Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255.
- 8-bit single-channel images (CV_8UC1) are not supported due to GIF's limitation to indexed color formats.
- With AVIF encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
- CV_16U images can be saved as only 10-bit or 12-bit (not 16-bit). See IMWRITE_AVIF_DEPTH.
- CV_16U images can be saved as only 10-bit or 12-bit (and 16-bit with libavif 1.4.0+). See @ref IMWRITE_AVIF_DEPTH.
- AVIF images with an alpha channel can be saved using this function.
To achieve this, create an 8-bit 4-channel (CV_8UC4) / 16-bit 4-channel (CV_16UC4) BGRA image, ensuring the alpha channel is the last component.
Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255 (8-bit) / 1023 (10-bit) / 4095 (12-bit) (see the code sample below).
Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255 (8-bit) / 1023 (10-bit) / 4095 (12-bit) / 65535 (16-bit) (see the code sample below).
Note that if the alpha plane contains only fully opaque pixels, the destination saves only color channels due to a libavif limitation.
If the image format is not supported, the image will be converted to 8-bit unsigned (CV_8U) and saved that way.