Can you help me understand this "wrong colormap" bug/problem?

Hi, everybody:

I filed a bug about Gimp after some checking, it was declared INVALID
and I was referred here to ask how to fix it. I'm running Gimp 2.6.6
on Ubuntu 9.04.

I get bad results when saving images after Gimp converts the colormap.
Its described here:

http://bugzilla.gnome.org/show_bug.cgi?id=567551

The lcms author and Sven Neumann looked into it and concluded it is
not a fault of the Gimp, but rather it is something wrong in the
original image. Images have Adobe1998 colormap embedded, but
apparently that is a mistake. I don't know how they can tell what the
colormap is, and I don't understand why the original image looks fine
in GQView but it does not look fine after editing in the Gimp. If I
bring the original image into Gimp and refuse Gimp's invitation to
convert the colormap, and save the image, it is displayed fine in
GQView. But if Gimp resets the colormap in any way, the image looks
bad.

I just don't get it.

On a practical level, what is a user supposed to do?

1. How am I supposed to know if the wrong colormap is embedded in an image?

2. How can I follow Sven's advice to "unset" the colormap? In Gimp
menus, I find only tools to convert or set the colormap, but not to
unset it.

PJ

On Fri, Jul 10, 2009 at 2:27 PM, Paul Johnson <pauljohn32@gmail.com> wrote:

> Hi, everybody:
>
> I filed a bug about Gimp after some checking, it was declared INVALID
> and I was referred here to ask how to fix it. I'm running Gimp 2.6.6
> on Ubuntu 9.04.
>
> I get bad results when saving images after Gimp converts the colormap.
> Its described here:
>
> http://bugzilla.gnome.org/show_bug.cgi?id=567551
>
> The lcms author and Sven Neumann looked into it and concluded it is
> not a fault of the Gimp, but rather it is something wrong in the
> original image. Images have Adobe1998 colormap embedded, but
> apparently that is a mistake. I don't know how they can tell what the
> colormap is, and I don't understand why the original image looks fine
> in GQView but it does not look fine after editing in the Gimp. If I
> bring the original image into Gimp and refuse Gimp's invitation to
> convert the colormap, and save the image, it is displayed fine in
> GQView. But if Gimp resets the colormap in any way, the image looks
> bad.


That's because the original color profile incorrectly specifies the meaning
of the colors; garbage in, garbage out.


>
> I just don't get it.
>
> On a practical level, what is a user supposed to do?
>
> 1. How am I supposed to know if the wrong colormap is embedded in an image?
>
> 2. How can I follow Sven's advice to "unset" the colormap? In Gimp
> menus, I find only tools to convert or set the colormap, but not to
> unset it.
>

First: you are not talking about colormaps (that is an entire different
issue, related to indexed images such as GIF. You are talking about ICC
color profiles.

1. Image Properties (ALT-Enter) has a tab devoted to describing the ICC
profile.

2. I would guess you should try to assign the default sRGB profile to this
image -- as all 'dumb' (ICC-unaware) programs will display images as if they
are sRGB, because most monitors approximate sRGB.

David