Re: [GM-help] understanding Magick::ImageType with indexed images

[Carnë D. <car...@gm...>]

On 18 July 2013 20:10, Bob Friesenhahn <bfr...@si...> wrote:
> On Thu, 18 Jul 2013, Carnė Draug wrote:
>>
>> So there's absolutely no way to find this? Not even an ugly hack? Or
>> would it be possible for me to implement a method in GraphicsMagick to
>> do so? If so, could you give me some pointers about where I should
>> look?
>
>
> Each coder module (around 100 of them already) deciphers the input image
> based on its knowledge of the format.  If the input file contains multiple
> frames, then is it possible that the frames are of different types so a
> whole-file value would not work.  The information would need to be at the
> per-frame level.
>
> I don't know of a way to solve this other than to update all of these coder
> modules to add an attribute to the image which indicates what the original
> format is.
>
> Alternatively, an option could be added to force never promoting monochrome
> and grayscale images to PseudoClass.  This might require writing new decode
> logic because the existing implementation might only be via PseudoClass.

I see the advantage of why GM might be doing this, it can reduce
memory usage a lot and it's really smart. I'd just really need a
method to get information on the original image.

>> Octave is using GraphicsMagick as the library to read and write
>> images, and we need to always returns the image as its stored in the
>> file, indexes or actual color values. Could you give me advice on the
>> best work this out?
>
>
> One way would be to do the work to produce a source patch for GraphicsMagick
> to add this information.  This would require some detailed work and research
> into the details of each file format.

I have looked into this and it's more work than what I can contribute
at the moment. I'm sorry. This issue does not seem to arise very
often, so I'll check the coder and if it's JPEG always treat it was
DirectClass. I understand that it won't always work but I can't fix
this the right way (which is in GM) right now.

Thank you,
Carnë