[dooglus@gmail.com: problem with transparent PNG image display]

[dooglus@gmail.com: problem with transparent PNG image display]

[Richard Stallman]

Would someone please DTRT and ack?

------- Start of forwarded message -------
Date: Wed, 10 Jan 2007 01:49:59 +0100
From: Chris Moore <dooglus@gmail.com>
To: emacs-pretest-bug@gnu.org
Subject: problem with transparent PNG image display
X-Spam-Status: No, score=0.0 required=5.0 tests=RCVD_BY_IP autolearn=failed 
	version=3.0.4

Download this image and open it in Emacs:

  http://tango-project.org/static/cvs/tango-art-tools/palettes/Tango-Palette.png

The image has lots of transparent pixels.  Using M-x
set-background-colour RET and you'll see the background of the image
changes with the background.

Now use 'convert' from ImageMagick to make a copy of the image:

  $ convert Tango-Palette.png Tango-Palette-copy.png

Open the new copy in Emacs and the transparent pixels show up as white
pixels.  Open the copy in The GIMP or gqview and you can see that the
background really is still transparent.

I'm using this version of convert:

  Version: ImageMagick 6.2.4 12/13/06 Q16 http://www.imagemagick.org
  Copyright: Copyright (C) 1999-2005 ImageMagick Studio LLC


In GNU Emacs 22.0.92.40 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2007-01-09 on trpaslik
X server distributor `The X.Org Foundation', version 11.0.70101000
configured using `configure  '--with-gtk' '--prefix' '/usr/local' '--with-xpm' '--with-jpeg' '--with-png' '--with-gif''


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------- End of forwarded message -------

Re: [dooglus@gmail.com: problem with transparent PNG image display]

[Chris Moore]

Richard Stallman <rms@gnu.org> writes:

> Would someone please DTRT and ack?
>
> From: Chris Moore <dooglus@gmail.com>

> I'm using this version of convert:
>
>   Version: ImageMagick 6.2.4 12/13/06 Q16 http://www.imagemagick.org
>   Copyright: Copyright (C) 1999-2005 ImageMagick Studio LLC

I notice that ImageMagic 6.3.0 is available and has changed things to
do with transparency.  I don't know if this is relevant, but Emacs
should support the .png files created by ImageMagic 6.2.4, assuming
that they are indeed valid.

Re: [dooglus@gmail.com: problem with transparent PNG image display]

[Chong Yidong]

> From: Chris Moore <dooglus@gmail.com>
>
> Download this image and open it in Emacs:
>
>   http://tango-project.org/static/cvs/tango-art-tools/palettes/Tango-Palette.png
>
> The image has lots of transparent pixels.  Using M-x
> set-background-colour RET and you'll see the background of the image
> changes with the background.

Umm, no it doesn't (check again).  Emacs 22 does not support
dynamically changing background colors, because that would involve
loading a new image object, and no one has gotten around to writing
the necessary code.  See image.c:6375.

Png images can specify what color to draw the background in if a
browser cannot handle arbitrary transparencies (this is the "Save
background color" option in Gimp).  The png code in Emacs fills in the
image background with the current frame background iff this background
color is unspecified.  This is why the `convert'ed png shows a white
background in Emacs, whereas the original png used whatever background
color your frame had---because imagemagick defaults to a white
background, whereas the original png did not specify it.  Again, note
that using M-x set-background-color RET will NOT change the background
color of the displayed image.

I think this bug should be removed from FOR-RELEASE.  Someone should,
however, work on this after the release.

> Now use 'convert' from ImageMagick to make a copy of the image:
>
>   $ convert Tango-Palette.png Tango-Palette-copy.png
>
> Open the new copy in Emacs and the transparent pixels show up as white
> pixels.  Open the copy in The GIMP or gqview and you can see that the
> background really is still transparent.
>
> I'm using this version of convert:
>
>   Version: ImageMagick 6.2.4 12/13/06 Q16 http://www.imagemagick.org
>   Copyright: Copyright (C) 1999-2005 ImageMagick Studio LLC

Re: [dooglus@gmail.com: problem with transparent PNG image display]

[Chris Moore]

Chong Yidong <cyd@stupidchicken.com> writes:

>> From: Chris Moore <dooglus@gmail.com>
>>
>> Using M-x set-background-colour RET and you'll see the background
>> of the image changes with the background.
>
> Umm, no it doesn't (check again).

Hmmm, that's right.  I thought I saw it change.  Maybe I was doing a
C-x C-v RET to get it to change.

> The png code in Emacs fills in the image background with the current
> frame background iff this background color is unspecified.

I don't think that's quite true.  The behaviour seems to be a little
more complex than that.  For example (where image.png is a transparent
PNG in the current directory with unspecified background colour):

  $ emacs -Q

  M-x set-background-color RET blue RET
  C-x b xxx RET
  C-x i image.png RET
  M-x image-mode RET    -> blue background, as expected.

  M-x set-background-color RET red RET
  C-x b yyy RET
  C-x i image.png RET
  M-x image-mode RET    -> blue background, not red.

> I think this bug should be removed from FOR-RELEASE.  Someone
> should, however, work on this after the release.

Agreed.

Re: [dooglus@gmail.com: problem with transparent PNG image display]

[Richard Stallman]

    I think this bug should be removed from FOR-RELEASE.  Someone should,
    however, work on this after the release.

I will delete it from FOR-RELEASE, or you can.  Can you add a suitable
entry to TODO, giving the information you have stated about the
nature of the issue?

Re: [dooglus@gmail.com: problem with transparent PNG image display]

[Chong Yidong]

Richard Stallman <rms@gnu.org> writes:

>     I think this bug should be removed from FOR-RELEASE.  Someone should,
>     however, work on this after the release.
>
> I will delete it from FOR-RELEASE, or you can.  Can you add a suitable
> entry to TODO, giving the information you have stated about the
> nature of the issue?

Done.