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SubjectRe: [PATCH v4 3/4] gpu: ipu-v3: ipu-ic: Add support for BT.709 encoding
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On Fri, 2019-02-08 at 17:47 -0800, Steve Longerbeam wrote:
> Pass v4l2 encoding enum to the ipu_ic task init functions, and add
> support for the BT.709 encoding and inverse encoding matrices.
>
> Reported-by: Tim Harvey <tharvey@gateworks.com>
> Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
> ---
> Changes in v4:
> - fix compile error.
> Chnges in v3:
> - none.
> Changes in v2:
> - only return "Unsupported YCbCr encoding" error if inf != outf,
> since if inf == outf, the identity matrix can be used. Reported
> by Tim Harvey.
> ---
> drivers/gpu/ipu-v3/ipu-ic.c | 71 +++++++++++++++++++--
> drivers/gpu/ipu-v3/ipu-image-convert.c | 1 +
> drivers/staging/media/imx/imx-ic-prpencvf.c | 4 +-
> include/video/imx-ipu-v3.h | 5 +-
> 4 files changed, 71 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/ipu-v3/ipu-ic.c b/drivers/gpu/ipu-v3/ipu-ic.c
> index e459615a49a1..c5f83d7e357f 100644
> --- a/drivers/gpu/ipu-v3/ipu-ic.c
> +++ b/drivers/gpu/ipu-v3/ipu-ic.c
> @@ -212,6 +212,23 @@ static const struct ic_csc_params ic_csc_identity = {
> .scale = 2,
> };
>
> +/*
> + * BT.709 encoding from RGB full range to YUV limited range:
> + *
> + * Y = R * .2126 + G * .7152 + B * .0722;
> + * U = R * -.1146 + G * -.3854 + B * .5000 + 128.;
> + * V = R * .5000 + G * -.4542 + B * -.0458 + 128.;

This is a conversion to YUV full range. Limited range should be:

Y   R * .1826 + G *  .6142 + B *  .0620 + 16;
U = R * -.1007 + G * -.3385 + B *  .4392 + 128;
V   R * .4392 + G * -.3990 + B * -.0402 + 128;

> + */
> +static const struct ic_csc_params ic_csc_rgb2ycbcr_bt709 = {
> + .coeff = {
> + { 54, 183, 18 },
> + { 483, 413, 128 },
> + { 128, 396, 500 },
> + },
> + .offset = { 0, 512, 512 },
> + .scale = 1,
> +};
> +
> /*
> * Inverse BT.601 encoding from YUV limited range to RGB full range:
> *
> @@ -229,12 +246,31 @@ static const struct ic_csc_params ic_csc_ycbcr2rgb_bt601 = {
> .scale = 2,
> };
>
> +/*
> + * Inverse BT.709 encoding from YUV limited range to RGB full range:
> + *
> + * R = (1. * (Y - 16)) + (1.5748 * (Cr - 128));
> + * G = (1. * (Y - 16)) - (0.1873 * (Cb - 128)) - (0.4681 * (Cr - 128));
> + * B = (1. * (Y - 16)) + (1.8556 * (Cb - 128);

The coefficients look like full range again, conversion from limited
range YUV should look like:

R = (1.1644 * (Y - 16)) + (1.7927 * (Cr - 128));
G = (1.1644 * (Y - 16)) - (0.2132 * (Cb - 128)) - (0.5329 * (Cr - 128));
B = (1.1644 * (Y - 16)) + (2.1124 * (Cb - 128);

> + */
> +static const struct ic_csc_params ic_csc_ycbcr2rgb_bt709 = {
> + .coeff = {
> + { 128, 0, 202 },
> + { 128, 488, 452 },
> + { 128, 238, 0 },
> + },
> + .offset = { -435, 136, -507 },
> + .scale = 2,
> +};
> +
> static int init_csc(struct ipu_ic *ic,
> enum ipu_color_space inf,
> enum ipu_color_space outf,
> + enum v4l2_ycbcr_encoding encoding,

Should we support YUV BT.601 <-> YUV REC.709 conversions? That would
require separate encodings for input and output. Also, this might be a
good time to think about adding quantization range parameters as well.

regards
Philipp

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