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Using GIMP on Mac OS X

Feb 19, 2011, 19:28
Post: #1
Using GIMP on Mac OS X
Here's a complete newbie question. Even though I've had GIMP on my Macs for at least 5 years, spanning 10.4, 10.5, and now 10.6, on an old half-sphere iMac, a MacBook Pro, and now a 27" flat-screen iMac, I have never been very good at using it. I've never gotten past the "open a .jpg and resize it" level of facility.

Why? Because I can't figure out how to make about 80% of the functionality work!

For instance, right now, I've got GIMP 2.6.11 on Mac OS X 10.6.6 on a quad-core iMac Core i7 machine. I want to drag part of an image to somewhere else in the image. I have just used the lasso to select part of the image I want to move. I have the correct Layer selected that contains the image. In the Toolbox, I've selected the Move tool, and in the Move options at the bottom, I've selected the red box to indicate that I want to move the selection, not the layer or the path. I go back to the image window by clicking inside it. My cursor shows an arrow, a crosshair, and a small selection box. According to the documentation at, Section 2.1.2 - Moving the other selections, I should be able to use Ctrl - Alt - click-n-drag to move my image selection wherever I want.


I have tried every combination of finger-twisting key manipulations I can think of with Shift, Ctrl, Alt, and Command, and nothing I do succeeds in moving that piece of the image. I've even tried using the set of Shift-Control-Command-Alt keys on the right side of the keyboard separate from the ones on the left side, just in case that makes a difference. About half the key combinations I've come up with, including Shift-Alt (or Alt-Shift, in case order is important), move the lasso selection itself, and the other half, including Shift-Ctrl (or Ctrl-Shift) switch from the Move Selection cursor to the Move Path cursor (an arrow, a circle with a bar through it, and part of a curve with a line tangent to it at a little square intersection point). Nothing moves the image contents though.


I have always had this feeling that there's something fundamental about using GIMP on a Mac that I'm simply missing. But in my occasional searches I haven't learned what it is. I must have a key binding wrong, or there's something set wrong in my X11 Preferences, or something. Can anyone help me get my computer set up so that GIMP works the way it should?

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Feb 19, 2011, 22:11 (This post was last modified: Feb 19, 2011 23:11 by ofnuts.)
Post: #2
RE: Using GIMP on Mac OS X
Your error is that the doc you see explains how to move the selection when the current tool is one of the selection tools (in other words, it is some form of "edit" mode for these tools)

But by your own description you are using the Move tool, and what you describe is its normal behavior, since, with it, "Moving the selection" is moving the bits indicating which pixels are selected, not moving the selected pixels (otherwise the doc would talk about "selection contents").

To make it short you should have used these key combos while still using the lasso tool.

I have heard that the OSX version may have some differences with the Windows and Linux ones (due to the use of a capricious X11 implementation, and this may be why the doc you refer to hints to press the Alt key first) but on the whole Gimp's behavior is fairly system-independent.

Anyway, in the general case, what you want to do is better handled by selection, then using copy/paste (or cut/paste) to create a floating selection, and then create a new layer that will be created with the selected contents (you can also use "paste as new layer"). This gives you a lot more control on the moved bits (scaling, rotation, color effects...) and if you used "copy" your original layer is left unchanged which may prove useful later.

PS: if you use Gimp to rescale pictures, make sure, using the preferences dialog, that its default scaling uses Sinc/Lanczos, and learn to use the "Unsharp Mask" filter to re-sharpen (yes!) the pictures after scaling them down.

Now answering your questions on
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Feb 25, 2011, 04:46
Post: #3
RE: Using GIMP on Mac OS X
Thanks, Ofnuts. The copy and paste-as-new-layer method seems to work pretty well.

I still can't get the move method to work, regardless of whether a Move tool or a Selection tool is the active tool. I don't know why, but at least I have a way to do what I want.

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Mar 3, 2011, 23:40
Post: #4
RE: Using GIMP on Mac OS X
Same problem here. Ctrl+Alt behaves as it should in Gimp for Windows7, doesn't for OSX. Copy/Paste does work, but having the same interface on all platforms saves frustration.
I've gotten it working for myself, so I figured I'd post here.

There's some patronizing advice here (, which suggests that the problem is with the default X11 key mapping in Leopard.

So, I followed steps 1 to 4 of this:
, with the following modification:
Change the line: "keycode 66 = Mode_switch" to "keycode 66 = Alt_L"
Change the line: "keycode 69 = Mode_switch" to "keycode 69 = Alt_R"

I quit X11, restarted GIMP, and now it works. Hope this helps somebody else.

There's a utility called xev (type "xev" in terminal, both OSX or X11) that you can use to see if the modifications to .Xmodmap worked. If you're seeing Alt_L and Alt_R when you hit the option keys in the X11 terminal, Ctrl+Alt+ClickAndDrag should work as well.
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