> Date: Fri, 9 Aug 2002 20:16:29 +0200
> From: Simon Budig <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Subject: Re: [Gimp-developer] Copy/Paste problem between layers
> Thierry Tracol ([EMAIL PROTECTED]) wrote:
> > With Gimp for Windows - version 1.2.3, I do the following operations :
> > 1. Start with a base image
> > 2. Make an elliptical selection (I have also the problem with other
> > kinds of selection).
> > 3. Copy it, clear it.
> > 4. Put the floating selection into a new layer L1
> > 5. In layer L1, go to step 2 throw step 4 and create layer L2
> > 6. ....
> Although I have problems to follow your steps (after step 3 there is
> no floating selection) I guess I know what your problem is: It is
> inherent to the way most image manipulation programs handle layers
> and not a bug in the GIMP.
To be more precise, step 4 should be : "Paste (ctrl-v), rename the floating
> > In theory, the base image should be split into the different layers.
> > With all the eye icons on, we should see the original base image.
> Nope, this is not true and ignores, that there is the concept of
> partially selected pixels - where "partially" means a percentage
> and not a specific part of a pixel.
> The problem is the same as in the following procedure:
> 1) Create new (white) image and select an (antialiased) ellipse
> 2) fill the ellipse with black
> 3) fill the ellipse with white.
> Step 3 is the opposite of step 2 - so the image should be completely
> white. But if you disable the selection you see that there is a
> faint gray border around the former ellipse. The reason for this is,
> that some of the pixels at the border have been partially selected.
> Lets look at a pixel that is selected 50%.
> In step 1 it is white. After filling it with black it is
> 50% black (since it was not fully selected). Now we fill it with
> white again: it becomes 25% black ((1 - 0.5) * original color + 0.5 *
> new color). So we have a slight gray pixel there and it is perfectly
I have tried your procedure. It works well if you remove the antialiasing
option with the elliptical selection tool.
The problem I have described still happens with no antialiasing selected.
The gap which appears between layers positions can be much more than one
In fact, it is not a problem specific to Gimp, since the same manipulation
with Photoshop gives the same kind of problems.
> The same can happen when you place two partially transparent pixels
> on top of each other in two layers: 50% opacity in the first and 50%
> opacity in the second layer does not sum up to 100% opacity, it is
> around 75% opacity (the math is basically the same). So if you
> cut out an ellipse and place it in a second layer on the very same
> place you will get a slightly transparent border around the ellipse.
> There is no way to fix this except filling the area in the lower
> layer with a background color.
> Hope this helps.
> [EMAIL PROTECTED] http://www.home.unix-ag.org/simon/
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