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Re: Gimp: Erased sections of images print in some cases
From: Earl Hood <earl () earlhood com>
Date: Tue, 29 Oct 2002 23:10:35 -0600

On October 30, 2002 at 11:08, Clark Mills wrote:

As part of documenting processes, I take screen captures and then chop
stuff out that I don't want the world to see.  I do this within the Gimp
by setting an alpha channel on the screen capture and then _erasing_ the
parts of the image that I want to obscure.  An example is at:

   http://c-mills.ctru.auckland.ac.nz/transparent.png

If you view this image from Linux in Galeon 1.2.6 or Netscape/7.0 all
looks fine however if you print the image from within these applications
then the _erased_ section prints as if it was never erased.

This could be a great bit of fun and a way of making print pages appear
with extra content that wasn't visible on the web page (pr0n,
copyright).

You can view the image without the alpha channel with ImageMagick:

  display -gamma 1.0,1.0,1.0,0.0 transparent.png

Also, in Gimp, you can decompose the RGB channels to see what is there.

On windows the images obscure which is great but obviously the _erased_
information is still in the sent image.

I let the Gimp people know this but they replied considering it a
feature not a bug which could be the case in some/most circumstances,
Bug #97167.

I think their explanation skirts the problem.  Basically, in your
case, the eraser does nothing.  When using the eraser, it should
erase whatever is there, even if the affected region is completely
transparent.

At a minimum, they should document better the behavior of the eraser.
Looking at the online help description:

  "If used on a normal floating layer, the color will be replaced
   with transparency."

This leaves it up-in-the-air if the actual color data is erased, or
if the opacity has just been hard-coded to 0 for the affected region.

The current behavior appears to be counter-intuitive to what
a user expects, it should either be documented better (maybe as a
caution since unintended data could then be viewed by others) or it
should be fixed.

My $0.02,

--ewh
-- 
Earl Hood, <earl () earlhood com>
Web: <http://www.earlhood.com/>
PGP Public Key: <http://www.earlhood.com/gpgpubkey.txt>


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