Re: [PATCH v6 2/7] gpu: ipu-v3: ipu-ic: Fix BT.601 coefficients
From: Steve Longerbeam
Date: Fri Mar 08 2019 - 20:00:30 EST
On 3/8/19 2:23 AM, Philipp Zabel wrote:
Hi Steve,
On Thu, 2019-03-07 at 15:33 -0800, Steve Longerbeam wrote:
The ycbcr2rgb and inverse rgb2ycbcr tables define the BT.601 Y'CbCr
encoding coefficients.
The rgb2ycbcr table specifically describes the BT.601 encoding from
full range RGB to full range YUV. Add table comments to make this more
clear.
The ycbcr2rgb inverse table describes encoding YUV limited range to RGB
full range. To be consistent with the rgb2ycbcr table, convert this to
YUV full range to RGB full range, and adjust/expand on the comments.
The ic_csc_rgb2rgb table is just an identity matrix, so rename to
ic_encode_identity.
Fixes: 1aa8ea0d2bd5d ("gpu: ipu-v3: Add Image Converter unit")
Suggested-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
Signed-off-by: Steve Longerbeam <slongerbeam@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/gpu/ipu-v3/ipu-ic.c | 61 ++++++++++++++++++++++---------------
1 file changed, 37 insertions(+), 24 deletions(-)
diff --git a/drivers/gpu/ipu-v3/ipu-ic.c b/drivers/gpu/ipu-v3/ipu-ic.c
index 18816ccf600e..b63a2826b629 100644
--- a/drivers/gpu/ipu-v3/ipu-ic.c
+++ b/drivers/gpu/ipu-v3/ipu-ic.c
@@ -175,7 +175,7 @@ static inline void ipu_ic_write(struct ipu_ic *ic, u32 value, unsigned offset)
writel(value, ic->priv->base + offset);
}
-struct ic_csc_params {
+struct ic_encode_coeff {
This less accurate. These are called IC (Task) Parameters in the
reference manual, the 64-bit aligned words are called CSC words. Beside
the coefficients, this structure also contains the coefficient scale,
the offsets, and the saturation mode flag.
It seemed to me the renaming was more clear, but I agree the former name
conforms better to the manual nomenclature. I will revert this renaming.
s16 coeff[3][3]; /* signed 9-bit integer coefficients */
s16 offset[3]; /* signed 11+2-bit fixed point offset */
u8 scale:2; /* scale coefficients * 2^(scale-1) */
@@ -183,13 +183,15 @@ struct ic_csc_params {
};
/*
- * Y = R * .299 + G * .587 + B * .114;
- * U = R * -.169 + G * -.332 + B * .500 + 128.;
- * V = R * .500 + G * -.419 + B * -.0813 + 128.;
+ * BT.601 encoding from RGB full range to YUV full range:
+ *
+ * Y = .2990 * R + .5870 * G + .1140 * B
+ * U = -.1687 * R - .3313 * G + .5000 * B + 128
+ * V = .5000 * R - .4187 * G - .0813 * B + 128
*/
-static const struct ic_csc_params ic_csc_rgb2ycbcr = {
+static const struct ic_encode_coeff ic_encode_rgb2ycbcr_601 = {
.coeff = {
- { 77, 150, 29 },
+ { 77, 150, 29 },
{ 469, 427, 128 },
{ 128, 405, 491 },
We could subtract 512 from the negative values, to improve readability.
Agreed.
},
@@ -197,8 +199,11 @@ static const struct ic_csc_params ic_csc_rgb2ycbcr = {
.scale = 1,
};
-/* transparent RGB->RGB matrix for graphics combining */
-static const struct ic_csc_params ic_csc_rgb2rgb = {
+/*
+ * identity matrix, used for transparent RGB->RGB graphics
+ * combining.
+ */
+static const struct ic_encode_coeff ic_encode_identity = {
.coeff = {
{ 128, 0, 0 },
{ 0, 128, 0 },
@@ -208,17 +213,25 @@ static const struct ic_csc_params ic_csc_rgb2rgb = {
};
/*
- * R = (1.164 * (Y - 16)) + (1.596 * (Cr - 128));
- * G = (1.164 * (Y - 16)) - (0.392 * (Cb - 128)) - (0.813 * (Cr - 128));
- * B = (1.164 * (Y - 16)) + (2.017 * (Cb - 128);
+ * Inverse BT.601 encoding from YUV full range to RGB full range:
+ *
+ * R = 1. * Y + 0 * (Cb - 128) + 1.4020 * (Cr - 128)
+ * G = 1. * Y - .3442 * (Cb - 128) - 0.7142 * (Cr - 128)
Should that be ^^^^^ .3441 and ^^^^^ .7141 ?
The coefficients and offsets after rounding should end up the same.
Ok.
Also, let's consistently either add the leading zero, or leave it out.
Yes.
+ * B = 1. * Y + 1.7720 * (Cb - 128) + 0 * (Cr - 128)
+ *
+ * equivalently (factoring out the offsets):
+ *
+ * R = 1. * Y + 0 * Cb + 1.4020 * Cr - 179.456
+ * G = 1. * Y - .3442 * Cb - 0.7142 * Cr + 135.475
+ * B = 1. * Y + 1.7720 * Cb + 0 * Cr - 226.816
*/
-static const struct ic_csc_params ic_csc_ycbcr2rgb = {
+static const struct ic_encode_coeff ic_encode_ycbcr2rgb_601 = {
.coeff = {
- { 149, 0, 204 },
- { 149, 462, 408 },
- { 149, 255, 0 },
+ { 128, 0, 179 },
+ { 128, 468, 421 },
+ { 128, 227, 0 },
},
- .offset = { -446, 266, -554 },
+ .offset = { -359, 271, -454 },
These seem to be correct. Again, I think this would be easier to read if
the negative coefficients were written with a sign as well.
.scale = 2,
};
@@ -228,7 +241,7 @@ static int init_csc(struct ipu_ic *ic,
int csc_index)
{
struct ipu_ic_priv *priv = ic->priv;
- const struct ic_csc_params *params;
+ const struct ic_encode_coeff *coeff;
u32 __iomem *base;
const u16 (*c)[3];
const u16 *a;
@@ -238,26 +251,26 @@ static int init_csc(struct ipu_ic *ic,
(priv->tpmem_base + ic->reg->tpmem_csc[csc_index]);
if (inf == IPUV3_COLORSPACE_YUV && outf == IPUV3_COLORSPACE_RGB)
- params = &ic_csc_ycbcr2rgb;
+ coeff = &ic_encode_ycbcr2rgb_601;
else if (inf == IPUV3_COLORSPACE_RGB && outf == IPUV3_COLORSPACE_YUV)
- params = &ic_csc_rgb2ycbcr;
+ coeff = &ic_encode_rgb2ycbcr_601;
else if (inf == IPUV3_COLORSPACE_RGB && outf == IPUV3_COLORSPACE_RGB)
- params = &ic_csc_rgb2rgb;
+ coeff = &ic_encode_identity;
else {
dev_err(priv->ipu->dev, "Unsupported color space conversion\n");
return -EINVAL;
}
/* Cast to unsigned */
- c = (const u16 (*)[3])params->coeff;
- a = (const u16 *)params->offset;
+ c = (const u16 (*)[3])coeff->coeff;
+ a = (const u16 *)coeff->offset;
This looks weird to me. I'd be in favor of not renaming the type.
Ok.
Steve