ここで base image、alternate image ついて説明しておく。それぞれ以下を意味している。
base image: Adobe の Gain Map仕様書の Base Rendition を意味する
alternate image: Base Rendition でない方の Rendition を意味する
Appendix2: libavif の avifgainmaputil の combine コマンドの help
参考情報として avifgainmaputil combine -help の内容を記載しておく。
$ avifgainmaputil combine -help
usage: avifgainmaputil combine base_image alternate_image output_image.avif
[--downscaling DOWNSCALING] [--qgain-map QGAIN-MAP]
[--depth-gain-map {8, 10, 12}] [--yuv-gain-map {444, 422, 420, 400}]
[--cicp-base CICP-BASE] [--cicp-alternate CICP-ALTERNATE] [-s SPEED]
[-q QCOLOR] [--qalpha QALPHA] [-y {444, 422, 420, 400}]
[-d {0, 8, 10, 12}] [--ignore-profile] [-h]
Creates an avif image with a gain map from a base image and an alternate image.
arguments:
base_image The base image, that will be shown by viewers that don't
support gain maps
alternate_image The alternate image, the result of fully applying the gain
map
output_image.avif
--downscaling DOWNSCALING
Downscaling factor for the gain map (Default: 1)
--qgain-map QGAIN-MAP
Quality for the gain map (0-100, where 100 is lossless) (Default: 60)
--depth-gain-map {8, 10, 12}
Output depth for the gain map (Default: 8)
--yuv-gain-map {444, 422, 420, 400}
Output format for the gain map (Default: 444)
--cicp-base CICP-BASE
Set or override the cicp values for the base image,
expressed as P/T/M where P = color primaries, T = transfer
characteristics, M = matrix coefficients.
--cicp-alternate CICP-ALTERNATE
Set or override the cicp values for the alternate image,
expressed as P/T/M where P = color primaries, T = transfer
characteristics, M = matrix coefficients.
-s SPEED, --speed SPEED
Encoder speed (0-10, slowest-fastest) (Default: 6)
-q QCOLOR, --qcolor QCOLOR
Quality for color (0-100, where 100 is lossless) (Default: 60)
--qalpha QALPHA Quality for alpha (0-100, where 100 is lossless) (Default: 100)
-y {444, 422, 420, 400}, --yuv {444, 422, 420, 400}
Output YUV format for avif (default = automatic)
-d {0, 8, 10, 12}, --depth {0, 8, 10, 12}
Output depth (0 = automatic)
--ignore-profile If the input file contains an embedded color profile, ignore
it (no-op if absent) (Default: false)
-h, --help Shows this help message
