[Haskell-cafe] Mini-announce: AC-Color 1.1.3

Yitzchak Gale gale at sefer.org
Tue Mar 9 07:37:19 EST 2010

Andrew Coppin wrote:
> I just uploaded a new version of the AC-Colour package...

Thanks for this.

Your algorithm for scaling brightness is not correct however.
The RGB values in all popular image formats are not linear.
They use a gamma transfer function. So your algorithm
will indeed change the colors in an image, not just its
brightness. In some cases the change in color can be quite
drastic. For a long-winded explanation and many examples,


You may want to implement one of the popular gamma transfer
functions, such as BT.709 or sRGB. The former may also be
useful for your AC-PPM package, since the PPM image format
uses it, as specified in its documentation:


sRGB is used in most other popular image formats
on the web nowadays.

> Colour maps. Give it some control points, and it'll
> (linearly) interpolate between them

Your algorithm for this is actually not linear at all, since RGB
values are generally not linear, as above.


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