Hi Pekka,
On 17/04/2025 11:13, Pekka Paalanen wrote:
My understanding is that the Y-only pixel formats behave in a well
defined way (or, as well defined as the YUV formats), and there's
nothing more to add here. Is that right?
There are two things:
- Y8 follows COLOR_RANGE property, just like all other YUV formats.
- Y8 implies that Cb and Cr are both neutral (0.0 in nominal values).
I'd like these explicitly written down, so that they become obvious to
everyone. I suspect either one might be easy to forget when writing
code and taking shortcuts without thinking.
I didn't find a suitable place in the docs for this, but would this, in
the drm_fourcc.h, be enough:
/*
* Y-only (greyscale) formats
*
* The Y-only formats are handled similarly to the YCbCr formats in the
display
* pipeline, with the Cb and Cr implicitly neutral (0.0 in nominal
values). This
* also means that COLOR_RANGE property applies to the Y-only formats.
*
*/
#define DRM_FORMAT_Y8 fourcc_code('G', 'R', 'E', 'Y') /* 8-bit
Y-only */
#define DRM_FORMAT_Y10_P32 fourcc_code('Y', 'P', 'A', '4') /* [31:0]
x:Y2:Y1:Y0 2:10:10:10 little endian */
Tomi
