Re: MagickGetImageAttribute and a transparency question

On Mon, 21 Jan 2013, Manfred Rebentisch wrote:

> Hello Bob,
> there is the function MagickGetImageAttribute() in magick_wand. How can
> I found the possible values for the parameter <name>??
>
> And the other question:
> How can I determine, whether an image has transparency?

These are good questions.

The image may have attributes which are stored as members in the image 
structure and don't have attribute names and so they can't be accessed 
via MagickGetImageAttribute().  Other attributes are stored as 
key/value and can be returned by MagickGetImageAttribute(). Look at 
the documentation for -format in the gm manual page for how IPTC and 
EXIF names are composed and the names which are documented to be 
available.

You can also do

   gm identify -verbose file.jpg

on an image file which is likely to contain the attributes you are 
interested in and see what is reported.

For the question about transparency, the only/best method I see is to 
use MagickGetImageType() and check if the returned value is one of 
GrayscaleMatteType, PaletteMatteType, TrueColorMatteType, or 
ColorSeparationMatteType.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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