[libcamera-devel] [PATCH 7/8] libcamera: v4l2_videodevice: Map V4L2_PIX_FMT_GREY to DRM FourCC

[Nicolas Dufresne]

Le samedi 14 mars 2020 à 01:38 +0200, Laurent Pinchart a écrit :
> DRM has a format for 8-bit greyscale data, DRM_FORMAT_R8. Despite the
> 'R' name, which comes from GL/Vulkan to mean single-channel data, the
> format maps to greyscale for display. We can thus map it to
> V4L2_PIX_FMT_GREY.

The mapping looks fine to me, but may lead to surprising result in
absence of colorimetry support. Most YCbCr 4:0:0 will be limited range,
while on the GFX side, most of R8 usage will be full range. Just be
aware.

Nicolas

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index f68b67b33293..f89bf2ff781e 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1473,12 +1473,15 @@ PixelFormat V4L2VideoDevice::toPixelFormat(uint32_t v4l2Fourcc)
>  	case V4L2_PIX_FMT_NV21M:
>  		return DRM_FORMAT_NV21;
>  
> +	/* Greyscale formats. */
> +	case V4L2_PIX_FMT_GREY:
> +		return DRM_FORMAT_R8;
> +
>  	/* Compressed formats. */
>  	case V4L2_PIX_FMT_MJPEG:
>  		return DRM_FORMAT_MJPEG;
>  
>  	/* V4L2 formats not yet supported by DRM. */
> -	case V4L2_PIX_FMT_GREY:
>  	default:
>  		/*
>  		 * \todo We can't use LOG() in a static method of a Loggable
> @@ -1557,6 +1560,10 @@ uint32_t V4L2VideoDevice::toV4L2Fourcc(PixelFormat pixelFormat, bool multiplanar
>  	case DRM_FORMAT_NV21:
>  		return V4L2_PIX_FMT_NV21;
>  
> +	/* Greyscale formats. */
> +	case DRM_FORMAT_R8:
> +		return V4L2_PIX_FMT_GREY;
> +
>  	/* Compressed formats. */
>  	case DRM_FORMAT_MJPEG:
>  		return V4L2_PIX_FMT_MJPEG;