On 02-Oct-2009, Daniel Kahn Gillmor wrote: > A few more things that are missing (i just ran into this while > trying to convert some private scripts from imagemagick to > graphicsmagick-imagemagick-compat:
I ran into this also, in trying to package a software work that uses
some ImageMagick commands. I assumed that, since I have
‘graphicsmagick-imagemagick-compat’ installed, that would suffice. Not
so.
> graphicsmagick-imagemagick-compat does not know about the Alpha
> channel -- it knows about Opacity, but the convert wrapper
> apparently isn't smart enough to translate between the synonyms.
> (or is alpha actually 1-opacity? i'm not sure)
According to the ImageMagick documentation:
Note that the channel names 'Alpha' ('A'), 'Opacity' ('O'), and
'Matte', are also aliases for the "-channel" setting referring to
the images transparency information. It does not matter that an
'alpha' channel is the inverse of a 'matte' channel, it still
refers to the same channel, and produces the same result.
Whether the data in that channel is acted upon a 'alpha' channel
data or as a 'matte' channel data, depend of the operator. Low
level channel operators like "-threshold" work on the raw 'matte'
data of the channel in memory. However most higher level operators
like "-fx" and "-composite" treat that data as representing
'alpha' data, for operation purposes.
<URL:http://www.imagemagick.org/Usage/channels/>
> This means i've had to revert to imagemagick, after a fair amount of
> debugging and searching for the promised "compatibility".
Likewise.
> Perhaps the long description of the package should indicate that it is
> not fully-compatible, and the specifics of the known incompatibilities
> could be dropped into
> /usr/share/doc/graphicsmagick-imagemagick-compat/incompatibilities.txt
Ideally, of course there would be enough interest in graphicsmagick as
a replacement to implement the features compatibly and submit changes
upstream :-)
--
\ “Only the educated are free.” —Epictetus, _Discourses_ |
`\ |
_o__) |
Ben Finney <b...@benfinney.id.au>
signature.asc
Description: Digital signature
