GNOME Bugzilla – Bug 340486
center of rotation
Last modified: 2008-01-15 13:07:20 UTC
When rotating entire images, sometimes the result is "off center" and moving it back to a correct position results in cropping of the areas that were out of bounds after the rotation. Also, image integrity is not preserved very well. For example, if you rotate a solid black bordered white box, grey will begin to appear. I think the preservation should be more "hard" and bitmap like, and the "center" of a rotated object unless respecified, should consider the original bounding rectangle rather than the center point only, because images of even-numbered pixel dimensions have no center pixel about which to rotate. On flipping, I can't seem to find a vertical flip option, only horizontal. (this may be because I just can't find it) Other information: Thanks for providing an open source image editor of this level, and thanks for entertaining bug reports and feedback.
Finding the horizontal flip: Double click on the flip tool button, or if you are using the default set up, look at the dialog just below the toolbox; you can toggle the direction of the flip that way. gimp versions: Also, you are using an old gimp which is unsupported. That being said, I don't think that anything has changed in regards to these tools since then though. off center images: See Image/Fit Canvas to Image. preservation of solid black lines: see #152593
See bug 152593 (sorry the first mention did not produce a link in bugzilla). Other information: Don't blame me!
Mike, how exactly do you rotate the image? Please give a detailed example that includes size of the image and its layers and tell us exactly what you are doing.
Created attachment 66701 [details] Before 90 degree Rotation
Created attachment 66702 [details] After 90 degree rotation
Sorry for the long delay, I've been away. Here is the information requested in comment #3. Also, thanks for clarifying on the flip issue. Attachments included. From a default install of GIMP 2.2.8 on Ubuntu 5.10, OR a default install of GIMP 2.2.11 on Ubuntu 6.06: (no steps have been omitted) 1. Open GIMP and create a new image with both width and height of 32 pixels. 2. Set magnification to 800% to observe the process better. 3. Select the Circle (01) (1 x 1) Brush 4. Select the "Paint Hard Edged Pixels" tool. 5. Draw a solid black line of 1 pixel width around all 4 borders of the image. 5. Draw a line to serve as a reference as to the current rotation of the image. I will draw a line from the top edge of the box towards the center, as if it were a hand on a clock pointing to 12 o'clock. My line is from 16,0 to 16,16 . 6. From the Edit menu, choose "Select All" 7. From the Tools menu, choose "Tools > Transform Tools > Rotate" 8. Enter 90 for the angle and click "Rotate" 9. My results are: a 1px black line from 1,0 to 1,31 a 1px black line from 1.0 to 31,0 a 1px black line from 16,17 to 31,17 a 1px black line from 1,1 to 17,1 ...hardly what I expected. Hope this helps. By default, am I in some sort of automatic adjustment mode for the things I draw? If so, I need the mode where my lines aren't "fiddled with" but I haven't been able to find evidence of such a scenario. I want to draw a 32x32 image, save it as image1.gif, rotate it, make a small change, save it as image2.gif, repeat, repeat, etc. Thank you very much, Mike
You should really not use the Rotate tool for this but the Rotate 90 degrees functions from the Transform menu. But then, the rotate tool is of course supposed to handle this correctly.
The problem with the center of rotation is something that should be solved, but the problem with accumulating error is intrinsically unsolvable in a raster-graphics program. The only way to do repeated small rotations, with manipulations in between, without accumulating error, is to use a vector-graphics program such as Inkscape. (Depending on exactly what you are trying to do, it is possible that you might manage it in GIMP using paths, but that's not very likely.)
I think the incorrect center is handled in bug #363775. Resolving as duplicate (even though this bug is older, but the other one has the possibly fixing commit message). Please reopen if you disagree. *** This bug has been marked as a duplicate of 363775 ***