[PATCH 2/3] apps: common: dng_writer: Add thumbnail scanline function for RawXX

[David Plowman]

Hi Stefan

Looks good to me!

On Thu, 27 Jun 2024 at 13:53, Stefan Klug <stefan.klug at ideasonboard.com> wrote:
>
> Add a thumbnail function for raw formats that are 16bit aligned.
> This is needed for the upcoming RAW10 and RAW12 implemntation.
>
> Use the new function for RAW16 as the thumbScanlineRawXX_CSI2P produces
> incorrect results for that format (it averages over adjacent bytes,
> which works for the CSI formats).
>
> Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> ---
>  src/apps/common/dng_writer.cpp | 32 ++++++++++++++++++++++++++++----
>  1 file changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/src/apps/common/dng_writer.cpp b/src/apps/common/dng_writer.cpp
> index 88b225d3e099..2cb320ff327b 100644
> --- a/src/apps/common/dng_writer.cpp
> +++ b/src/apps/common/dng_writer.cpp
> @@ -144,6 +144,30 @@ void packScanlineRaw16(void *output, const void *input, unsigned int width)
>         std::copy(in, in + width, out);
>  }
>
> +/* Thumbnail function for raw data aligned to 16bit words */
> +void thumbScanlineRawXX(const FormatInfo &info, void *output,
> +                         const void *input, unsigned int width,
> +                         unsigned int stride)
> +{
> +       const uint16_t *in = static_cast<const uint16_t *>(input);
> +       const uint16_t *in2 = static_cast<const uint16_t *>(input) + stride / 2;
> +       uint8_t *out = static_cast<uint8_t *>(output);
> +
> +       /* shift down to 8 */
> +       unsigned int shift = info.bitsPerSample - 8;
> +
> +       /* simple averaging that produces grey RGB values */
> +       for (unsigned int x = 0; x < width; x++) {
> +               uint16_t value = (in[0] + in[1] + in2[0] + in2[1]) >> 2;
> +               value = value >> shift;
> +               *out++ = value;
> +               *out++ = value;
> +               *out++ = value;

Just a small question as to whether you might want to subtract some
black level and apply some "fake" gamma? It might make the thumbnails
look a bit nicer. But just a matter of taste, I think, not something
I'd worry over!

David

> +               in += 16;
> +               in2 += 16;
> +       }
> +}
> +
>  void packScanlineRaw10_CSI2P(void *output, const void *input, unsigned int width)
>  {
>         const uint8_t *in = static_cast<const uint8_t *>(input);
> @@ -321,25 +345,25 @@ const std::map<PixelFormat, FormatInfo> formatInfo = {
>                 .bitsPerSample = 16,
>                 .pattern = { CFAPatternBlue, CFAPatternGreen, CFAPatternGreen, CFAPatternRed },
>                 .packScanline = packScanlineRaw16,
> -               .thumbScanline = thumbScanlineRawXX_CSI2P,
> +               .thumbScanline = thumbScanlineRawXX,
>         } },
>         { formats::SGBRG16, {
>                 .bitsPerSample = 16,
>                 .pattern = { CFAPatternGreen, CFAPatternBlue, CFAPatternRed, CFAPatternGreen },
>                 .packScanline = packScanlineRaw16,
> -               .thumbScanline = thumbScanlineRawXX_CSI2P,
> +               .thumbScanline = thumbScanlineRawXX,
>         } },
>         { formats::SGRBG16, {
>                 .bitsPerSample = 16,
>                 .pattern = { CFAPatternGreen, CFAPatternRed, CFAPatternBlue, CFAPatternGreen },
>                 .packScanline = packScanlineRaw16,
> -               .thumbScanline = thumbScanlineRawXX_CSI2P,
> +               .thumbScanline = thumbScanlineRawXX,
>         } },
>         { formats::SRGGB16, {
>                 .bitsPerSample = 16,
>                 .pattern = { CFAPatternRed, CFAPatternGreen, CFAPatternGreen, CFAPatternBlue },
>                 .packScanline = packScanlineRaw16,
> -               .thumbScanline = thumbScanlineRawXX_CSI2P,
> +               .thumbScanline = thumbScanlineRawXX,
>         } },
>         { formats::SBGGR10_CSI2P, {
>                 .bitsPerSample = 10,
> --
> 2.43.0
>