Re: [PATCH v5 1/3] [media] exynos-gsc: Use user configured colorspace if provided

From: Thibault Saunier
Date: Wed Feb 22 2017 - 08:06:19 EST


On 02/21/2017 11:19 PM, Hans Verkuil wrote:

On 02/21/2017 11:20 AM, Thibault Saunier wrote:
Use colorspace provided by the user as we are only doing scaling and
color encoding conversion, we won't be able to transform the colorspace
itself and the colorspace won't mater in that operation.

Also always use output colorspace on the capture side.

Start using 576p as a threashold to compute the colorspace.
The media documentation says that the V4L2_COLORSPACE_SMPTE170M colorspace
should be used for SDTV and V4L2_COLORSPACE_REC709 for HDTV. But drivers
don't agree on the display resolution that should be used as a threshold.

From EIA CEA 861B about colorimetry for various resolutions:

- 5.1 480p, 480i, 576p, 576i, 240p, and 288p
The color space used by the 480-line, 576-line, 240-line, and 288-line
formats will likely be based on SMPTE 170M [1].
- 5.2 1080i, 1080p, and 720p
The color space used by the high definition formats will likely be
based on ITU-R BT.709-4

This indicates that in the case that userspace does not specify what
colorspace should be used, we should use 576p as a threshold to set
V4L2_COLORSPACE_REC709 instead of V4L2_COLORSPACE_SMPTE170M. Even if it is
only 'likely' and not a requirement it is the best guess we can make.

The stream should have been encoded with the information and userspace
has to pass it to the driver if it is not the case, otherwise we won't be
able to handle it properly anyhow.

Also, check for the resolution in G_FMT instead unconditionally setting
the V4L2_COLORSPACE_REC709 colorspace.

Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx>
Signed-off-by: Thibault Saunier <thibault.saunier@xxxxxxxxxxxxxxx>
Reviewed-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>


Changes in v5:
- Squash commit to always use output colorspace on the capture side
inside this one
- Fix typo in commit message

Changes in v4:
- Reword commit message to better back our assumptions on specifications

Changes in v3:
- Do not check values in the g_fmt functions as Andrzej explained in previous review
- Added 'Reviewed-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>'

Changes in v2: None

drivers/media/platform/exynos-gsc/gsc-core.c | 20 +++++++++++++++-----
drivers/media/platform/exynos-gsc/gsc-core.h | 1 +
2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/media/platform/exynos-gsc/gsc-core.c b/drivers/media/platform/exynos-gsc/gsc-core.c
index 59a634201830..772599de8c13 100644
--- a/drivers/media/platform/exynos-gsc/gsc-core.c
+++ b/drivers/media/platform/exynos-gsc/gsc-core.c
@@ -454,6 +454,7 @@ int gsc_try_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
} else {
min_w = variant->pix_min->target_rot_dis_w;
min_h = variant->pix_min->target_rot_dis_h;
+ pix_mp->colorspace = ctx->out_colorspace;
pr_debug("mod_x: %d, mod_y: %d, max_w: %d, max_h = %d",
@@ -472,10 +473,15 @@ int gsc_try_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
pix_mp->num_planes = fmt->num_planes;
- if (pix_mp->width >= 1280) /* HD */
- pix_mp->colorspace = V4L2_COLORSPACE_REC709;
- else /* SD */
- pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
+ if (pix_mp->colorspace == V4L2_COLORSPACE_DEFAULT) {
+ if (pix_mp->width > 720 && pix_mp->height > 576) /* HD */
I'd use || instead of && here. Ditto for the next patch.

+ pix_mp->colorspace = V4L2_COLORSPACE_REC709;
+ else /* SD */
+ pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
+ }
Are you sure this is in fact how it is used? If the source of the video
is the sensor (camera), then the colorspace is typically SRGB. I'm not
really sure you should guess here. All a mem2mem driver should do is to
pass the colorspace etc. information from the output to the capture side,
and not invent things. That simply makes no sense.

This is not a camera device but a colorspace conversion device, in many
cases the info will not be passed by the userspace, basically because the info
is not encoded in the media stream (this often happens). I am not inventing here,
just making sure we use the most likely value in case none was provided (and if none
was provided it should always be correct given that the encoded stream was not broken).

In the case the source is a camera and then we use the colorspace converter then the info
should copied from the camera to the transcoding node (by userspace) so there should be
no problem.

What I am doing here is what is done in other drivers.



We may have to update the documentation or v4l2-compliance test if this
is an issue. The more I think about this, the more I think we shouldn't
do this guessing game.



+ if (V4L2_TYPE_IS_OUTPUT(f->type))
+ ctx->out_colorspace = pix_mp->colorspace;
for (i = 0; i < pix_mp->num_planes; ++i) {
struct v4l2_plane_pix_format *plane_fmt = &pix_mp->plane_fmt[i];
@@ -519,9 +525,13 @@ int gsc_g_fmt_mplane(struct gsc_ctx *ctx, struct v4l2_format *f)
pix_mp->height = frame->f_height;
pix_mp->field = V4L2_FIELD_NONE;
pix_mp->pixelformat = frame->fmt->pixelformat;
- pix_mp->colorspace = V4L2_COLORSPACE_REC709;
pix_mp->num_planes = frame->fmt->num_planes;
+ if (pix_mp->width > 720 && pix_mp->height > 576) /* HD */
+ pix_mp->colorspace = V4L2_COLORSPACE_REC709;
+ else /* SD */
+ pix_mp->colorspace = V4L2_COLORSPACE_SMPTE170M;
for (i = 0; i < pix_mp->num_planes; ++i) {
pix_mp->plane_fmt[i].bytesperline = (frame->f_width *
frame->fmt->depth[i]) / 8;
diff --git a/drivers/media/platform/exynos-gsc/gsc-core.h b/drivers/media/platform/exynos-gsc/gsc-core.h
index 696217e9af66..715d9c9d8d30 100644
--- a/drivers/media/platform/exynos-gsc/gsc-core.h
+++ b/drivers/media/platform/exynos-gsc/gsc-core.h
@@ -376,6 +376,7 @@ struct gsc_ctx {
struct v4l2_ctrl_handler ctrl_handler;
struct gsc_ctrls gsc_ctrls;
bool ctrls_rdy;
+ enum v4l2_colorspace out_colorspace;
void gsc_set_prefbuf(struct gsc_dev *gsc, struct gsc_frame *frm);