Che Burashka on wrote...
| Hi, Ron,
|
| > But isn't it also relevant that GIF does not support
| > partial transparency?
|
| This is right. However, I would expect ImageMagick to
| dither the image properly. It does that, as you can
| see on the images I posted, but the results are not
| correct. I can also see the difference when trying
| different levels of opacity; so it does try to dither
| it.
|
IM will not automatically dither semi-transparent pixels. It will
threshold them at a 50% level.
This is on purpose as most people know that GIF does not handle
transparency so do not generate semi-transparent pixels. As such the
only semi-transparency that is present is typically some edges as a
result of drawing or resizing of images. These need to be thresholded
or you end up with a very bad uneven looking edge.
If you want to dither transparency, DIY it.
See IM Examples
Color Quantization and transparency
http://www.cit.gu.edu.au/~anthony/graphics/imagick6/quantize/#color_trans
The examples in the above should eventually move to its own section.
Also the transparency dithering in GIF format handleing...
http://www.cit.gu.edu.au/~anthony/graphics/imagick6/formats/#dither
Would also move into that new section when it is created.
For other ways of handling GIF transparency see...
IM Examples, Common Image Formats
GIF Boolean Transparency
http://www.cit.gu.edu.au/~anthony/graphics/imagick6/formats/#boolean_trans
In your specific case Che, i suggest you avoid the transparency issue
and use the techniques in IM Examples to overlay the image on a
background of the appropriate color. It is about the only way of doing
it with GIF.
NOTE however that most webbrowsers can handle PNG, though IE6 will need
some special PNG handling code to do it at least partically.
Enjoy.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
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