possible reporting bug -list format for PNG

[fmw42]

convert -version
Version: ImageMagick 6.9.0-3 Q16 x86_64 2015-01-04 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2015 ImageMagick Studio LLC
Features: DPC Modules
Delegates (built-in): bzlib cairo fftw fontconfig freetype gslib jbig jng jp2 jpeg lcms lqr ltdl lzma openexr png ps rsvg tiff webp x xml zlib

Code: Select all

convert -list format

Produces the following;


PNG* PNG rw- Portable Network Graphics (libpng 1.6.12)
See http://www.libpng.org/ for details about the PNG format.
PNG00* PNG rw- PNG inheriting bit-depth and color-type from original
PNG24* PNG rw- opaque or binary transparent 24-bit RGB (zlib 1.2.
PNG32* PNG rw- opaque or transparent 32-bit RGBA
PNG48* PNG rw- opaque or binary transparent 48-bit RGB
PNG64* PNG rw- opaque or transparent 64-bit RGBA
PNG8* PNG rw- 8-bit indexed with optional binary transparency


Seems to me that "binary transparency" for PNG24: and PNG48: should be 8-bit and 16-bit transparency.

Am I misunderstanding something about the meaning of binary here?

Does "binary" here mean that it is simply a separate alpha channel as opposed to a reference to some color value that should be displayed as transparent as in PNG8:?

[glennrp]

Binary means only fully-opaque or fully-transparent are supported in the PNG24 and PNG48 sub-formats. It is GIF-style transparency wherein a single color is deemed to be transparent (via the tRNS chunk).

[fmw42]

Sorry for the false alarm. I don't know where my head was at that time.

I was mistakenly thinking PNG32 amd PNG64 when I wrote the message. But it is interesting to know that PNG24 and PNG48 actually support transparency like PNG8. I thought they supported no transparency.

Thanks Glenn.