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Message-ID: <d894d2a9-efeb-45ff-526c-05b4e57680cc@gmail.com>
Date: Fri, 8 Mar 2019 17:00:17 -0800
From: Steve Longerbeam <slongerbeam@...il.com>
To: Philipp Zabel <p.zabel@...gutronix.de>, linux-media@...r.kernel.org
Cc: Tim Harvey <tharvey@...eworks.com>, stable@...r.kernel.org,
"open list:DRM DRIVERS FOR FREESCALE IMX"
<dri-devel@...ts.freedesktop.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 2/7] gpu: ipu-v3: ipu-ic: Fix BT.601 coefficients
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@...gutronix.de>
>> Signed-off-by: Steve Longerbeam <slongerbeam@...il.com>
>> Cc: stable@...r.kernel.org
>> ---
>> 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
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