The arithmetic to process colors in premultiplied alpha is completely different from the arithmetic for straight alpha. Running a filter using straight arithmetic on premultiplied will result in incorrect and sometimes invalid output. Therefore, premultiplied alpha should only be selected for filters that either explicitly support it or only use elementary color arithmetic or none at all. For other filters, automatic conversion will do its work.
Signed-off-by: Nicolas George <[email protected]> --- libavfilter/formats.c | 15 ++++++++++++++- libavfilter/formats.h | 12 ++++++++++++ 2 files changed, 26 insertions(+), 1 deletion(-) diff --git a/libavfilter/formats.c b/libavfilter/formats.c index 3315922cc7..f4fd43370b 100644 --- a/libavfilter/formats.c +++ b/libavfilter/formats.c @@ -721,6 +721,14 @@ AVFilterFormats *ff_all_color_ranges(void) return ret; } +AVFilterFormats *ff_alpha_mode_straight(void) +{ + AVFilterFormats *ret = NULL; + if (ff_add_format(&ret, AVALPHA_MODE_STRAIGHT) < 0) + return NULL; + return ret; +} + AVFilterFormats *ff_all_alpha_modes(void) { AVFilterFormats *ret = NULL; @@ -950,6 +958,11 @@ int ff_set_common_alpha_modes_from_list(AVFilterContext *ctx, return ff_set_common_alpha_modes(ctx, ff_make_format_list(alpha_modes)); } +int ff_set_common_alpha_mode_straight(AVFilterContext *ctx) +{ + return ff_set_common_alpha_modes(ctx, ff_alpha_mode_straight()); +} + int ff_set_common_all_alpha_modes(AVFilterContext *ctx) { return ff_set_common_alpha_modes(ctx, ff_all_alpha_modes()); @@ -1214,7 +1227,7 @@ int ff_default_query_formats(AVFilterContext *ctx) ret = ff_set_common_all_color_ranges(ctx); if (ret < 0) return ret; - ret = ff_set_common_all_alpha_modes(ctx); + ret = ff_set_common_alpha_mode_straight(ctx); if (ret < 0) return ret; } diff --git a/libavfilter/formats.h b/libavfilter/formats.h index 45864a32db..cde86a40b1 100644 --- a/libavfilter/formats.h +++ b/libavfilter/formats.h @@ -144,6 +144,12 @@ AVFilterFormats *ff_all_color_spaces(void); av_warn_unused_result AVFilterFormats *ff_all_color_ranges(void); +/** + * Construct an AVFilterFormats with only premultiplied alpha. + */ +av_warn_unused_result +AVFilterFormats *ff_alpha_mode_straight(void); + /** * Construct an AVFilterFormats representing all possible alpha modes. */ @@ -227,6 +233,12 @@ av_warn_unused_result int ff_set_common_alpha_modes_from_list(AVFilterContext *ctx, const int *alpha_modes); +/** + * Equivalent to ff_set_common_alpha_modes(ctx, ff_alpha_mode_straight()) + */ +av_warn_unused_result +int ff_set_common_alpha_mode_straight(AVFilterContext *ctx); + /** * Equivalent to ff_set_common_alpha_modes(ctx, ff_all_alpha_modes()) */ -- 2.53.0 _______________________________________________ ffmpeg-devel mailing list -- [email protected] To unsubscribe send an email to [email protected]
