Re: [GD-DEVEL] GD Alpha Channel Values

Hi Steve,

On 4/18/07, Steve Lime <[email protected]> wrote:
> Hi all: We've been working on some integration work using AGG (www.antigrain.com) to render into GD image buffers. Works ok generally but there are problems with how each system treats the alpha channel. In GD 0 is fully opaque and AGG has 0 as fully transparent. In checking a few other sources online (libpng, cairo, w3c) it seems that 0 is always transparent. I guess my question is why GD is backwards and can anything be done about it. Thoughts?

History is hard to change :)

I do not remember if there is not an option to invert the alpha
channel (cairo has none as far as I can see). The second issue is
about the value, GD opacity level goes from 0 to 127, it is unusual.
How did you manage to work arount this problem?

However, the good news is that I plan to add new buffer format in
2.1.0. One of them is a 32bit ARGB. Other may be added as well as a
generic format. We may start to work on these surfaces in the
playground module? It may help to catch all possible issues.

I have a couple of questions about AGG and GD, I will try to post them
later (I did not get the time to play with gd-agg since our last
discussion). It may be good to see how far you got and see what I can
do in GD to help you and other developers :)

Cheers,
--Pierre