[Mesa-dev] [PATCH 18/29] util/srgb: Add a float sRGB -> linear helper

[Pohjolainen, Topi]

On Fri, Jan 26, 2018 at 05:59:47PM -0800, Jason Ekstrand wrote:
> ---
>  src/util/format_srgb.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/src/util/format_srgb.h b/src/util/format_srgb.h
> index 34b50af..596af56 100644
> --- a/src/util/format_srgb.h
> +++ b/src/util/format_srgb.h
> @@ -55,6 +55,20 @@ util_format_linear_to_srgb_helper_table[104];
>  
>  
>  static inline float
> +util_format_srgb_to_linear_float(float cs)
> +{
> +   if (cs <= 0.0f)
> +      return 0.0f;
> +   else if (cs <= 0.04045f)

In patch 8 you used open-ended: "cs < 0.04045f". As I mentioned in my reply
there, I don't know what is the correct form. But we should probably be
consistent between these two.

Looking the already existing util_format_linear_to_srgb_float() I see that it
uses equivalent open-ended "cl < 0.0031308f" as you did in patch 8.

The first search hit for me for the subject was:

http://entropymine.com/imageworsener/srgbformula/

which starts by close-ended "cs <= 0.04045f" but argues later on that
cs <= 0.0404482362771082 might be more accurate.

> +      return cs / 12.92f;
> +   else if (cs < 1.0f)
> +      return powf((cs + 0.055) / 1.055f, 2.4f);
> +   else
> +      return 1.0f;
> +}
> +
> +
> +static inline float
>  util_format_linear_to_srgb_float(float cl)
>  {
>     if (cl <= 0.0f)
> -- 
> 2.5.0.400.gff86faf
> 
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