> Date: Fri, 9 Aug 2002 20:16:29 +0200 > From: Simon Budig <Simon.Budig@xxxxxxxxxxx> > To: gimp-developer@xxxxxxxxxxxxxxxxxxxxxx > Subject: Re: [Gimp-developer] Copy/Paste problem between layers > > Thierry Tracol (thierry.tracol@xxxxxxxxxxxxxx) 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 selection L1" > > > > 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 > reasonable... > 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 pixel. 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. > > Bye, > Simon > -- > Simon.Budig@xxxxxxxxxxx http://www.home.unix-ag.org/simon/ > > --__--__-- > > _______________________________________________ > Gimp-developer mailing list > Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx > http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer > > End of Gimp-developer Digest
