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

[Jacopo Mondi]

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());
 	ret = resizer_->setSelection(0, V4L2_SEL_TGT_CROP, &rect);
 	if (ret < 0)
 		return ret;
-- 
2.40.1