Composite with different transparencies

[GreenKoopa]

I reported this as a bug:
viewtopic.php?f=3&t=17635

weatherbadger, I linked to your two images at weatherbadger.com. I'm sure the developers would appreciate you leaving them up, or providing new links in the above bug report.

[weatherbadger]

Hmm, I'm on 6.6.1-0 here. However, this is the latest version I can (it seems easily) get for Opensuse 11.3.

The other computer I have which the transparency composite works okay on is IM 6.5 something.

What does png32: do anyway - would that be version dependent?

tbc/night

[anthony]

HWhat does png32: do anyway - would that be version dependent?

It forces the PNG coder to use RGBA direct color channels rather than a indexed palette image.

A pallette image has one channel of index values, which is then used to look up what color that pixel should be from a table (a palette). GIF only allows 8 bit indexed palete (no other option) and thus is limited to 256 colors. I believe PNG allows for a 16 bit index (65536 colors), and even allows semi-transparency colors in the palette. It is indexed or palette PNG images that is being worked on.

By default the PNG coder will try to fine the best (smallest file producing) internal format for PNG. The new coder changes means it should be able to provide better palette images, but is experiencing bugs. Using png32: forces it to use a specific internal format (non-pallette).

[GreenKoopa]

I just tested the latest version and the bug is still there. At least the two of us have a workaround now.

What does png32: do anyway

PNG32: forces the 32-bit PNG format, that is 8 bits for each red, green, blue, and alpha transparency channels. Alternatively, you can use -define png:color-type=6 to force direct color (no palette) in either 32 (-depth 8 ) or 64 (-depth 16) bits. For RGB only (no transparency), PNG24: or -define png:color-type=2 would be used.

Further background reading at Wikipedia:
http://en.wikipedia.org/wiki/RGB_color_model#Truecolor
http://en.wikipedia.org/wiki/Indexed_color
http://en.wikipedia.org/wiki/Portable_Network_Graphics

[weatherbadger]

Hmpfh, I still can't get your workarounds (png:32 or -define png:color-type=6 ) to work. Still black instead of varying transparency (with IM 6.6.1-0)

For the record, the other computer I have with IM 6.5.4-8 works fine without any workarounds - perhaps I'll have to use that until a new release, unless you have any other suggestions.

[anthony]

It may be that your version was just after the bug was discovered, and before some of the bug fixes were added.

I would suggest you either use the latest version, or a slightly older version for the time being.