[libcamera-devel] [PATCH v3 4/5] libcamera: Add the transpose transformation

[Laurent Pinchart]

Hi Sebastian,

Thank you for the patch.

On Tue, Jan 26, 2021 at 07:48:53PM +0100, Sebastian Fricke wrote:
> To transpose a BayerFormat means to flip it over its main-diagonal.

s/main-diagonal/main diagonal/

> 
> For example:
> G B    G R
>     ->
> R G    B G
> 
> The main-diagonal goes from the top left to the bottom right.

Same here.

> This means, that the only two orders affected by a transpose
> are GBRG & GRBG. When a transpose is used in combination with horizontal
> and/or vertical flips it is performed with the lowest priority.
> Therefore add the functionality by switching GBRG (index 1) with GRBG
> (index 2), after the flips have been applied.
> 
> Signed-off-by: Sebastian Fricke <sebastian.fricke at posteo.net>
> ---
>  src/libcamera/bayer_format.cpp | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/src/libcamera/bayer_format.cpp b/src/libcamera/bayer_format.cpp
> index d4e7f142..e06cd6e8 100644
> --- a/src/libcamera/bayer_format.cpp
> +++ b/src/libcamera/bayer_format.cpp
> @@ -272,10 +272,6 @@ BayerFormat BayerFormat::fromV4L2PixelFormat(V4L2PixelFormat v4l2Format)
>   * The transformed image would have a GRBG order. The bit depth and modifiers
>   * are not affected.
>   *
> - * Note that transpositions are ignored as the order of a transpose with
> - * respect to the flips would have to be defined, and sensors are not expected
> - * to support transposition.
> - *

This needs to now document the order in which the flips and transpose
are applied. Maybe something along the lines of

  * Horizontal and vertical flips are applied before transpose.

With this change,

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

but I'd like to get David's feedback on this.

>   * \return The transformed Bayer format
>   */
>  BayerFormat BayerFormat::transform(Transform t) const
> @@ -292,6 +288,11 @@ BayerFormat BayerFormat::transform(Transform t) const
>  	if (!!(t & Transform::VFlip))
>  		result.order = static_cast<Order>(result.order ^ 2);
>  
> +	if (!!(t & Transform::Transpose) && result.order == 1)
> +		result.order = static_cast<Order>(2);
> +	else if (!!(t & Transform::Transpose) && result.order == 2)
> +		result.order = static_cast<Order>(1);
> +
>  	return result;
>  }
>  

-- 
Regards,

Laurent Pinchart