[libcamera-devel] [PATCH 4/4] ipu3: cio2: Tweak sensor size selection policy

[Jacopo Mondi]

Hi Umang,

On Tue, Aug 03, 2021 at 07:02:05PM +0530, Umang Jain wrote:
> Do not compare higher precision of the ratios, as it might lead to
> absurd selection of sensor size for a relatively low requested
> resolution size.
>
> For example:
> The imx258 driver supports the following sensor resolutions:
>
>  - 4208x3118 = 1.349583066
>  - 2104x1560 = 1.348717949
>  - 1048x780  = 1.343589744
>
> It can be inferred that, that the aspect ratio only differs by a small
> factor with each other. It does not makes sense to select a 4208x3118
> for a requested size of say 640x480 or 1280x720, which is what is
> happening currently.
> ($) cam -c1 -swidth=640,height=480,role=raw
>     - CIO2 configuration: 4208x3118-SGRBG10_IPU3
>
> In order to address this constraint, only compare the ratio with single
> precision to make a better decision on the sensor resolution policy
> selection.
>
> ($) cam -c1 -srole=raw,width=640,height=480
>     - CIO2 configuration: 1048x780-SGRBG10_IPU3
>
> Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
> ---
>  src/libcamera/pipeline/ipu3/cio2.cpp | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/src/libcamera/pipeline/ipu3/cio2.cpp b/src/libcamera/pipeline/ipu3/cio2.cpp
> index 9980b8bd..887b850d 100644
> --- a/src/libcamera/pipeline/ipu3/cio2.cpp
> +++ b/src/libcamera/pipeline/ipu3/cio2.cpp
> @@ -281,6 +281,13 @@ V4L2SubdeviceFormat CIO2Device::getSensorFormat(const std::vector<unsigned int>
>  				continue;
>
>  			float ratio = static_cast<float>(sz.width) / sz.height;
> +			/*
> +			 * Comparing ratios with a single precision is enough.
> +			 * This avoids the selection of a frame size which is
> +			 * 2x or 3x than the requested size, having a slightly
> +			 * better ratio w.r.t native resolution ratio.

Well, the fact the 2x or 3x sizes selection happens is Nautilus
specific. I would stay simple and just

                        /*
                         * Comparing rations with a single precision
                         * digit is enough.
                         */

Be aware that this actually truncates instead of rounding.. is this
the correct choice ? Also do we need to round the desired ratio too ?

Thanks
   j

> +			 */
> +			ratio = static_cast<unsigned int>(ratio * 10) / 10.0;
>  			float ratioDiff = fabsf(ratio - desiredRatio);
>  			unsigned int area = sz.width * sz.height;
>  			unsigned int areaDiff = area - desiredArea;
> --
> 2.31.0
>