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| author | Paul Kocialkowski <contact@paulk.fr> | 2018-11-23 12:24:55 +0300 |
|---|---|---|
| committer | Maxime Ripard <maxime.ripard@bootlin.com> | 2018-11-27 11:57:21 +0300 |
| commit | dc7d4b655a2c4a8db1342600319a7939eafeb9af (patch) | |
| tree | aeaba494575f48e09e170e4953ce7a397bc1d703 /drivers/gpu/drm/sun4i/sun4i_backend.c | |
| parent | b636d3f97d041cbb5e782a29b282c40cbd77c0aa (diff) | |
| download | linux-dc7d4b655a2c4a8db1342600319a7939eafeb9af.tar.xz | |
drm/sun4i: backend: Detail the YUV to RGB values coding explanation
The values in the BT601 YUV to RGB colorspace translation are not
simply coded as multiples, but rather as fixed-point signed fractional
values on a given number of bits. Add an explanation about that.
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181123092515.2511-24-paul.kocialkowski@bootlin.com
Diffstat (limited to 'drivers/gpu/drm/sun4i/sun4i_backend.c')
| -rw-r--r-- | drivers/gpu/drm/sun4i/sun4i_backend.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c index 2a9569f16c81..f43c4b0f1e5d 100644 --- a/drivers/gpu/drm/sun4i/sun4i_backend.c +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c @@ -48,8 +48,12 @@ static const u32 sunxi_rgb2yuv_coef[12] = { /* * These coefficients are taken from the A33 BSP from Allwinner. * - * The formula is for each component, each coefficient being multiplied by - * 1024 and each constant being multiplied by 16: + * The first three values of each row are coded as 13-bit signed fixed-point + * numbers, with 10 bits for the fractional part. The fourth value is a + * constant coded as a 14-bit signed fixed-point number with 4 bits for the + * fractional part. + * + * The values in table order give the following colorspace translation: * G = 1.164 * Y - 0.391 * U - 0.813 * V + 135 * R = 1.164 * Y + 1.596 * V - 222 * B = 1.164 * Y + 2.018 * U + 276 |