[FFmpeg-devel] [PATCH v2 1/8] swscale: document SWS_FULL_CHR_H_* flags

[Andrew Sayers]

On Thu, Jul 04, 2024 at 04:30:57PM +0200, Niklas Haas wrote:
> From: Niklas Haas <git at haasn.dev>
> 
> Based on my best understanding of what they do, given the source code.
> ---
>  libswscale/swscale.h | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/libswscale/swscale.h b/libswscale/swscale.h
> index 9d4612aaf3..e22931cab4 100644
> --- a/libswscale/swscale.h
> +++ b/libswscale/swscale.h
> @@ -82,11 +82,35 @@ const char *swscale_license(void);
>  #define SWS_PRINT_INFO              0x1000
>  
>  //the following 3 flags are not completely implemented
> -//internal chrominance subsampling info
> +
> +/**
> + * Perform full chroma upsampling when converting to RGB as part of scaling.

Nitpick: "as part of scaling" seems redundant - can it be removed?

> + *
> + * For example, when converting 50x50 yuv420p to 100x100 rgba, setting this flag
> + * will scale the chroma plane from 25x25 to 100x100 (4:4:4), and then convert
> + * the 100x100 yuv444p image to rgba in the final output step.
> + *
> + * Without this flag, the chroma plane is instead scaled to 50x100 (4:2:2),
> + * with a single chroma sample being re-used for both horizontally adjacent RGBA
> + * output pixels.

Nitpick: this would be more readable as "for both of the...".

Consider the following sentence:

    Without this flag, the chroma plane is instead scaled to 50x100 (4:2:2),
    with a single chroma sample being re-used for both horizontally and vertically
    adjacent RGBA output pixels.

Using "both of the" would make it clear what "both" refers to before the reader
starts doing branch-prediction in their head.

Otherwise, LGTM (by which I mean it's clear, not that I know whether it's
correct).