On Mon, 16 Dec 2024 14:56:07 +0100 Niklas Haas <ffm...@haasn.xyz> wrote:
> From: Niklas Haas <g...@haasn.dev>
>
> The current logic uses 12-bit linear light math, which is woefully
> insufficient
> and leads to nasty postarization artifacts. This patch simply switches the
> internal logic to 16-bit precision.
>
> This raises the memory requirement of these tables from 32 kB to 272 kB.
Will merge this one (with the FATE changes) in a few days if there are no
further objections.
Should we try and lazily allocate these tables to save the ~272 kB of static
memory or is that considered an insignificant amount?
>
> Fixes: ticket 4829
> Signed-off-by: Niklas Haas <g...@haasn.dev>
> Sponsored-by: Sovereign Tech Fund
> ---
> libswscale/swscale.c | 16 ++++++++--------
> libswscale/swscale_internal.h | 8 ++++----
> libswscale/utils.c | 19 ++++++++++++-------
> 3 files changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/libswscale/swscale.c b/libswscale/swscale.c
> index 96634acfd6..da3a082905 100644
> --- a/libswscale/swscale.c
> +++ b/libswscale/swscale.c
> @@ -773,10 +773,10 @@ void ff_xyz12Torgb48(const SwsInternal *c, uint8_t
> *dst, int dst_stride,
> c->xyz2rgb_matrix[2][1] * y +
> c->xyz2rgb_matrix[2][2] * z >> 12;
>
> - // limit values to 12-bit depth
> - r = av_clip_uintp2(r, 12);
> - g = av_clip_uintp2(g, 12);
> - b = av_clip_uintp2(b, 12);
> + // limit values to 16-bit depth
> + r = av_clip_uint16(r);
> + g = av_clip_uint16(g);
> + b = av_clip_uint16(b);
>
> // convert from sRGBlinear to RGB and scale from 12bit to 16bit
> if (desc->flags & AV_PIX_FMT_FLAG_BE) {
> @@ -832,10 +832,10 @@ void ff_rgb48Toxyz12(const SwsInternal *c, uint8_t
> *dst, int dst_stride,
> c->rgb2xyz_matrix[2][1] * g +
> c->rgb2xyz_matrix[2][2] * b >> 12;
>
> - // limit values to 12-bit depth
> - x = av_clip_uintp2(x, 12);
> - y = av_clip_uintp2(y, 12);
> - z = av_clip_uintp2(z, 12);
> + // limit values to 16-bit depth
> + x = av_clip_uint16(x);
> + y = av_clip_uint16(y);
> + z = av_clip_uint16(z);
>
> // convert from XYZlinear to X'Y'Z' and scale from 12bit to 16bit
> if (desc->flags & AV_PIX_FMT_FLAG_BE) {
> diff --git a/libswscale/swscale_internal.h b/libswscale/swscale_internal.h
> index 768e394560..5acd277b50 100644
> --- a/libswscale/swscale_internal.h
> +++ b/libswscale/swscale_internal.h
> @@ -547,10 +547,10 @@ struct SwsInternal {
> /* pre defined color-spaces gamma */
> #define XYZ_GAMMA (2.6f)
> #define RGB_GAMMA (2.2f)
> - int16_t *xyzgamma;
> - int16_t *rgbgamma;
> - int16_t *xyzgammainv;
> - int16_t *rgbgammainv;
> + uint16_t *xyzgamma;
> + uint16_t *rgbgamma;
> + uint16_t *xyzgammainv;
> + uint16_t *rgbgammainv;
> int16_t xyz2rgb_matrix[3][4];
> int16_t rgb2xyz_matrix[3][4];
>
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index 4dedbfc394..937e19f651 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/utils.c
> @@ -948,7 +948,8 @@ static void fill_xyztables(SwsInternal *c)
> {1689, 1464, 739},
> { 871, 2929, 296},
> { 79, 488, 3891} };
> - static int16_t xyzgamma_tab[4096], rgbgamma_tab[4096],
> xyzgammainv_tab[4096], rgbgammainv_tab[4096];
> + static uint16_t xyzgamma_tab[4096], rgbgammainv_tab[4096];
> + static uint16_t rgbgamma_tab[65536], xyzgammainv_tab[65536];
>
> memcpy(c->xyz2rgb_matrix, xyz2rgb_matrix, sizeof(c->xyz2rgb_matrix));
> memcpy(c->rgb2xyz_matrix, rgb2xyz_matrix, sizeof(c->rgb2xyz_matrix));
> @@ -957,15 +958,19 @@ static void fill_xyztables(SwsInternal *c)
> c->xyzgammainv = xyzgammainv_tab;
> c->rgbgammainv = rgbgammainv_tab;
>
> - if (rgbgamma_tab[4095])
> + if (xyzgamma_tab[4095])
> return;
>
> - /* set gamma vectors */
> + /* set input gamma vectors */
> for (i = 0; i < 4096; i++) {
> - xyzgamma_tab[i] = lrint(pow(i / 4095.0, xyzgamma) * 4095.0);
> - rgbgamma_tab[i] = lrint(pow(i / 4095.0, rgbgamma) * 4095.0);
> - xyzgammainv_tab[i] = lrint(pow(i / 4095.0, xyzgammainv) * 4095.0);
> - rgbgammainv_tab[i] = lrint(pow(i / 4095.0, rgbgammainv) * 4095.0);
> + xyzgamma_tab[i] = lrint(pow(i / 4095.0, xyzgamma) * 65535.0);
> + rgbgammainv_tab[i] = lrint(pow(i / 4095.0, rgbgammainv) * 65535.0);
> + }
> +
> + /* set output gamma vectors */
> + for (i = 0; i < 65536; i++) {
> + rgbgamma_tab[i] = lrint(pow(i / 65535.0, rgbgamma) * 4095.0);
> + xyzgammainv_tab[i] = lrint(pow(i / 65535.0, xyzgammainv) * 4095.0);
> }
> }
>
> --
> 2.47.0
>
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