[cairo] Converting to 8 bit black and white
ben.lists at bsb.me.uk
Tue Sep 25 08:52:02 PDT 2012
May be too late...
On Tue, 2012-09-18 at 13:36 -0500, Timothy Bolton wrote:
> I have another question. How do you convert a surface from color to 8
> bit black and white? I've been searching and I cannot seem to find a
> way to convert a surface to black and white.
> I'm pulling in images, and I need them to be black and white (not gray
> scale) for the rendering.
If you use CAIRO_OPERATOR_HSL_COLOR with a grey source you get a
grey-scale image. You can then threshold it by adding and burning with
the darkest non-black source you can construct:
cairo_t *cp = cairo_create(surf);
cairo_set_source_rgb(cp, t, t, t);
cairo_set_source_rgb(cp, DBL_MIN, DBL_MIN, DBL_MIN);
t is the level below which the result will be black.
There may be a neater way to do this, but this method was the first that
came to mind (I tend to stop once I have any solution).
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