[libcamera-devel] [PATCH v5 2/4] libcamera: rkisp1: Crop on ISP before downscaling

[Laurent Pinchart]

Hi Jacopo,

Thank you for the patch.

On Tue, Jun 06, 2023 at 12:33:34PM +0200, Jacopo Mondi via libcamera-devel wrote:
> Crop on the resizer sink pad before downscaling to the aspect ratio
> of the desired output size.
> 
> Cropping the input frame to the output aspect ratio allows to maintain
> the correct picture proportions, as otherwise downscaling would change
> the image geometry.
> 
> Signed-off-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
> Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>
> ---
>  src/libcamera/pipeline/rkisp1/rkisp1_path.cpp | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp b/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
> index 5079b268c464..0f728cea72b7 100644
> --- a/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
> +++ b/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
> @@ -314,7 +314,18 @@ int RkISP1Path::configure(const StreamConfiguration &config,
>  	if (ret < 0)
>  		return ret;
>  
> -	Rectangle rect(0, 0, ispFormat.size);
> +	/*
> +	 * Crop on the resizer input to maintain FOV before downscaling.
> +	 *
> +	 * \todo The alignment to a multiple of 2 pixels is required but may
> +	 * change the aspect ratio very slightly. A more advanced algorithm to
> +	 * compute the resizer input crop rectangle is needed, and it should
> +	 * also take into account the need to crop away the edge pixels affected
> +	 * by the ISP processing blocks.
> +	 */
> +	Size ispCrop = inputFormat.size.boundedToAspectRatio(config.size)
> +				       .alignedUpTo(2, 2);
> +	Rectangle rect = ispCrop.centeredTo(Rectangle(inputFormat.size).center());

I like the expressiveness of the geometry helpers :-)

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  	ret = resizer_->setSelection(0, V4L2_SEL_TGT_CROP, &rect);
>  	if (ret < 0)
>  		return ret;

-- 
Regards,

Laurent Pinchart