Re: Linear Colorspace

On 02/12/15 17:24, Bob Friesenhahn wrote
> Use:
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>     image.gamma(0.454545);  // 1/2.2
>     [ do something ]
>     image.gamma(2.2);
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Good enough for me for now. On a technical level, isn't this an 
approximation since sRGB doesn't have a constant gamma?

> The above should accomplish what the article recommends.  Keep in mind
> that whenever you apply a gamma correction change, the image is
> subject to quantization error (new value is subject to the number of
> discrete levels available).  The quantization error will be reduced by
> using a Q:16 build.
Right. I selected a quantum of 16 when I built the library for just this 
reason.
> There are factors other than gamma to consider such as the colorspace
> used.  This is a reason why there is a note in the documentation for
> -colors which says:
>
> "Empirical evidence suggests that distances in color spaces such as
> YUV or YIQ correspond to perceptual color differences more closely
> than do distances in RGB space.  These color spaces may give better
> results when color reducing an image."
>
> The same issues apply to resize and any other operations which blend
> pixels.
Are you suggesting that resizing in YUV or YIQ would yield better (or at 
least) the same results?

Thanks again,
Sam

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