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SubjectRe: [PATCH v4 1/4] gpu: ipu-v3: ipu-ic: Rename yuv2rgb encoding matrices
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On Fri, 2019-02-08 at 17:47 -0800, Steve Longerbeam wrote:
> The ycbcr2rgb and inverse rgb2ycbcr matrices define the BT.601 encoding
> coefficients, so rename them to indicate that. And add some comments
> to make clear these are BT.601 coefficients encoding between YUV limited
> range and RGB full range. The ic_csc_rgb2rgb matrix is just an identity
> matrix, so rename to ic_csc_identity. No functional changes.
>
> Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
> ---
> Changes in v2:
> - rename ic_csc_rgb2rgb matrix to ic_csc_identity.
> ---
> drivers/gpu/ipu-v3/ipu-ic.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/ipu-v3/ipu-ic.c b/drivers/gpu/ipu-v3/ipu-ic.c
> index 594c3cbc8291..3ef61f0b509b 100644
> --- a/drivers/gpu/ipu-v3/ipu-ic.c
> +++ b/drivers/gpu/ipu-v3/ipu-ic.c
> @@ -183,11 +183,13 @@ struct ic_csc_params {
> };
>
> /*
> + * BT.601 encoding from RGB full range to YUV limited range:
> + *
> * Y = R * .299 + G * .587 + B * .114;
> * U = R * -.169 + G * -.332 + B * .500 + 128.;
> * V = R * .500 + G * -.419 + B * -.0813 + 128.;

Hm, this is a conversion to full range BT.601. For limited range, the
matrix coefficients

0.2990  0.5870  0.1140
-0.1687 -0.3313  0.5000
0.5000 -0.4187 -0.0813

should be multiplied with 219/255 (Y) and 224/255 (U,V), respectively:

Y = R * .2568 + G * .5041 + B * .0979 + 16;
U = R * -.1482 + G * -.2910 + B *  .4392 + 128;
V = R * .4392 + G * -.3678 + B * -.0714 + 128;

> */
> -static const struct ic_csc_params ic_csc_rgb2ycbcr = {
> +static const struct ic_csc_params ic_csc_rgb2ycbcr_bt601 = {
> .coeff = {
> { 77, 150, 29 },
> { 469, 427, 128 },
> @@ -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_csc_params ic_csc_identity = {
> .coeff = {
> { 128, 0, 0 },
> { 0, 128, 0 },
> @@ -208,11 +213,13 @@ static const struct ic_csc_params ic_csc_rgb2rgb = {
> };
>
> /*
> + * Inverse BT.601 encoding from YUV limited range to RGB full range:
> + *
> * 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);
> */

This looks correct.

> -static const struct ic_csc_params ic_csc_ycbcr2rgb = {
> +static const struct ic_csc_params ic_csc_ycbcr2rgb_bt601 = {
> .coeff = {
> { 149, 0, 204 },
> { 149, 462, 408 },
> @@ -238,11 +245,11 @@ 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;
> + params = &ic_csc_ycbcr2rgb_bt601;
> else if (inf == IPUV3_COLORSPACE_RGB && outf == IPUV3_COLORSPACE_YUV)
> - params = &ic_csc_rgb2ycbcr;
> + params = &ic_csc_rgb2ycbcr_bt601;
> else if (inf == IPUV3_COLORSPACE_RGB && outf == IPUV3_COLORSPACE_RGB)
> - params = &ic_csc_rgb2rgb;
> + params = &ic_csc_identity;
> else {
> dev_err(priv->ipu->dev, "Unsupported color space conversion\n");
> return -EINVAL;

regards
Philipp

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