libcamera: bayer_format: Expand documentation

The current documentation of the BayerFormat::transform() function
reports examples on the Bayer components ordering transformation for
horizontal flip (mirroring) but not for vertical flip or for the
combination of the two.

It is useful to complete the documentation to ease understanding of the
transform() function on a sensor's Bayer pattern.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 13 insertions, 7 deletions

diff --git a/src/libcamera/bayer_format.cpp b/src/libcamera/bayer_format.cpp
index f27cc166..6a76d6a4 100644
--- a/src/libcamera/bayer_format.cpp
+++ b/src/libcamera/bayer_format.cpp
@@ -356,11 +356,14 @@ BayerFormat BayerFormat::fromPixelFormat(PixelFormat format)
  * \brief Apply a transform to this BayerFormat
  * \param[in] t The transform to apply
  *
- * Appplying a transform to an image stored in a Bayer format affects the Bayer
- * order. For example, performing a horizontal flip on the Bayer pattern
- * RGGB causes the RG rows of pixels to become GR, and the GB rows to become BG.
- * The transformed image would have a GRBG order. The bit depth and modifiers
- * are not affected.
+ * Applying a transform to an image stored in a Bayer format affects the Bayer
+ * order. For example, performing a horizontal flip on the Bayer pattern RGGB
+ * causes the RG rows of pixels to become GR, and the GB rows to become BG. The
+ * transformed image would have a GRBG order. Performing a vertical flip on the
+ * Bayer pattern RGGB causes the GB rows to come before the RG ones and the
+ * transformed image would have GBRG order. Applying both vertical and
+ * horizontal flips on the Bayer patter RGGB results in transformed images with
+ * BGGR order. The bit depth and modifiers are not affected.
  *
  * Horizontal and vertical flips are applied before transpose.
  *
@@ -375,8 +378,11 @@ BayerFormat BayerFormat::transform(Transform t) const
 
 	/*
 	 * Observe that flipping bit 0 of the Order enum performs a horizontal
-	 * mirror on the Bayer pattern (e.g. RGGB goes to GRBG). Similarly,
-	 * flipping bit 1 performs a vertical mirror operation on it. Hence:
+	 * mirror on the Bayer pattern (e.g. RG/GB goes to GR/BG). Similarly,
+	 * flipping bit 1 performs a vertical mirror operation on it (e.g RG/GB
+	 * goes to GB/RG). Applying both vertical and horizontal flips
+	 * combines vertical and horizontal mirroring on the Bayer pattern
+	 * (e.g. RG/GB goes to BG/GR). Hence:
 	 */
 	if (!!(t & Transform::HFlip))
 		result.order = static_cast<Order>(result.order ^ 1);