GNU bug report logs - #10746
ImageMagick and priority of image loaders

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Message #3 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: submit <at> debbugs.gnu.org
Subject: ImageMagick and priority of image loaders
Date: Mon, 06 Feb 2012 23:16:21 -0500

Package: emacs
Version: 24.0.93

The Emacs Lisp manual used to say (I'm going to comment it out, for the
reasons given in this report):

    There may be overlap between image loaders in your Emacs
    installation, and you may prefer to use a different one for a given
    image type (which loader will be used in practice depends on the
    priority of the loaders). For example, if you never want to use the
    ImageMagick loader to use JPEG files, add @code{JPG} to this list.

Firstly, I don't understand what this means. What does it means for
there to be multiple "image loaders" in Emacs, and how is their priority
determined? (Also, do I have to add JPEG as well, since
imagemagick-types returns both JPG and JPEG?)

I think it might mean, eg jpeg images can be loaded via libjpeg or
ImageMagick. If that is what it means, it could be clearer.

If so, when I view a jpg with Emacs, how can I tell which loader was
used? Maybe from looking at the mode-line in image-mode, which either
says [jpeg] or [imagemagick]?

It seems there's no practical way to control which loader is used:

i) If you compile without jpeg but with ImageMagick, then you simply cannot
view jpegs: http://debbugs.gnu.org/9045

ii) If you compile with both, then libjpeg is always used (AFAICS). This is
despite imagemagick-register-types adding to the front of
image-type-file-name-regexps. When you visit a jpeg file, image-type
first uses image-type-from-file-header to determine the image type, and
this decides it is a jpeg. So imagemagick never gets a change to open
the jpeg. You can make it work by setting image-type-header-regexps to
nil, but that is supposed to be a constant.

Message #6 received at 10746 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 10746 <at> debbugs.gnu.org, Joakim Verona <joakim <at> verona.se>
Subject: Re: bug#10746: ImageMagick and priority of image loaders
Date: Tue, 07 Feb 2012 05:42:57 +0100

Glenn Morris <rgm <at> gnu.org> writes:

> ii) If you compile with both, then libjpeg is always used (AFAICS).

Well, you can say so explicitly:

(create-image data 'imagemagick t)

-- 
(domestic pets only, the antidote for overdose, milk.)
  http://lars.ingebrigtsen.no  *  Sent from my Rome

Message #9 received at 10746 <at> debbugs.gnu.org (full text, mbox):

From: Wolfgang Jenkner <wjenkner <at> inode.at>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 10746 <at> debbugs.gnu.org, Joakim Verona <joakim <at> verona.se>
Subject: Re: bug#10746: ImageMagick and priority of image loaders
Date: Tue, 07 Feb 2012 06:02:45 +0100

See also the discussion of bug#10112.

Message #12 received at 10746 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 10746 <at> debbugs.gnu.org, Joakim Verona <joakim <at> verona.se>
Subject: Re: bug#10746: ImageMagick and priority of image loaders
Date: Wed, 25 Sep 2019 14:25:42 +0200

Glenn Morris <rgm <at> gnu.org> writes:

> The Emacs Lisp manual used to say (I'm going to comment it out, for the
> reasons given in this report):
>
>     There may be overlap between image loaders in your Emacs
>     installation, and you may prefer to use a different one for a given
>     image type (which loader will be used in practice depends on the
>     priority of the loaders). For example, if you never want to use the
>     ImageMagick loader to use JPEG files, add @code{JPG} to this list.
>
> Firstly, I don't understand what this means. What does it means for
> there to be multiple "image loaders" in Emacs, and how is their priority
> determined? (Also, do I have to add JPEG as well, since
> imagemagick-types returns both JPG and JPEG?)

This doesn't seem to be in the manual any more, and the rest of the bug
report doesn't seem to have any concrete bugs, so I'm closing this bug
report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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