Well, I'm not here to tell you guys how to implement your PNG8
support, but from the looks of it, you may be falling behind.
It looks like PNG8 partial transparency is part of the spec. From
http://www.libpng.org/pub/png/pngstatus.html :
"Many applications now support both basic GIF-like transparency
(palette-based with a single, fully transparent color index) and full
alpha transparency (32-bit RGBA); a handful also support PNG's "RGBA
palette" mode (8-bit with a multi-entry tRNS chunk)."
Example images are on this page:
http://www.libpng.org/pub/png/pngs-img.html
And it *even* looks like IE7 will be supporting PNG8 partial
transparency. See screen shots of previous page here:
http://www.libpng.org/pub/png/pngs-img-ie7w32.html
For more technical info, see here:
http://www.libpng.org/pub/png/book/chapter08.html#INDEX-618
As far as my "bug" goes: I just tried saving as a 24 bit PNG from
montage, then using pngquant to reduce the colors, and it worked
fine. I have the transparency like I wanted, with the palette I
wanted. Hopefully pngquant will also be able to handle my large (4 GB
uncompressed) images, but it will be a number of hours before I can
test that.
Maybe you should take a look at the pngquant source for quantization
algorithm ideas?
~Seth
On May 11, 2006, at 8:10 PM, Anthony Thyssen wrote:
Seth Price on wrote...
| Nope, it still doesn't work.
|
| PNG8 supports partial transparency (and has for a while). Internet
| Explorer only supports PNG8 boolean transparency, though. This has
| lead to limited use of partial transparency on the web.
|
| A quick google search pulled up this bug from a while ago:
| http://studio.imagemagick.org/pipermail/magick-bugs/2003-September/
| 001484.html
|
| I wonder if it's the same problem.
| ~Seth
|
It could very well be.
IM png8: is by defination the same pallette structure as GIF.
and so isn't incorrect in IM terms.
Prehaps a png8t: format is needed for a 8 bit pallet with partical
colors.
Their was some recent work done with color distances last March so
that
all pure transparency colors are of disance zero. This was needed for
layer optimizations as without it a near transparent colors can be
very
distant from each other, distorting color reduction and other color
tests (EG -fuzz color matching stuffs up badly)
This is a linear adjustment as such the RGBA distance between
half-transparent red to half-transparent blue is half the ditance of a
fully opaque red and blue distance.
Hmm my auto sinature picker picked a good on for this topic!
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
----------------------------------------------------------------------
-------
"Brigadier, a straight line may be the shortest distance between
two points,
but it is by no means the most interesting."
-- Doctor Who, "The Time
Warrior"
----------------------------------------------------------------------
-------
Anthony's Home is his Castle http://www.cit.gu.edu.au/
~anthony/
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