On Tue, 2008-07-08 at 09:56 -0600, ChadDavis wrote:

I've got a rectangle selection. Now, I am trying to do a subtractive selection within that rectangular selection, to make a sort of picture frame selection. The problem is that I'm having trouble getting the inner, substractive selection centered within the first rectangle.

Very common procedure (making a frame). I use this method to make an antialiased line around things:

1. Create a rectangular selection. 2. Fill with color
3. Shrink selection by X pixels (where x is the width of the border you want)
4. Cut selection (or fill with background color, etc.).

Alternatively, use the Tool Options dialog for the selection tool and set the Size and Position fields manually for the second selection. The first method works for small width borders but because shrink will slowly round the corners it doesn't work well for larger width borders. The second method works perfectly for all width borders.

Quoting ChadDavis :

I've got a rectangle selection. Now, I am trying to do a subtractive selection within that rectangular selection, to make a sort of picture frame selection. The problem is that I'm having trouble getting the inner, substractive selection centered within the first rectangle.

Draw your larger selection and save it to a channel.

Check the "Expand from center" option in the tool's Option dialog and then click inside the selection to activate the drag handles[*]. Use the handles to resize your rectangle.

Invert your selection and then intersect it with the previously saved channel (CTL+SHIFT the red button next to the trashcan in the Channels dialog).

[*] Even though the handles might be visible, they are not actually active after a "Select->Save to channel" is performed (this is probably a bug).

saulgoode@flashingtwelve.brickfilms.com writes:

Quoting ChadDavis :

I've got a rectangle selection. Now, I am trying to do a subtractive selection within that rectangular selection, to make a sort of picture frame selection. The problem is that I'm having trouble getting the inner, substractive selection centered within the first rectangle.

Draw your larger selection and save it to a channel.

Check the "Expand from center" option in the tool's Option dialog and then click inside the selection to activate the drag handles[*]. Use the handles to resize your rectangle.

Invert your selection and then intersect it with the previously saved channel (CTL+SHIFT the red button next to the trashcan in the Channels dialog).

Here's a simpler method (no need for saving to a channel) that I thought would work, but doesn't, and I'm not clear why:

1. Make the first selection. Click inside the rectangle to confirm it.

2. In the Rect Select tool options, switch to Subtract mode, Expand from Center, and Fixed Aspect Ratio (current).

3. Click in the rectangle again to bring back the resize handles.

4. Resize to define the smaller rectangle (which will be subtracted from the larger one.

The problem: when you first start the drag from a resize handle in step 4, the boundaries jump to a rectangle that's not concentric with the current one, with the positions seemingly random (at least, I can't see any regularity to which handle creates jumps in which direction).

Is that a bug? If it's not, why does it happen? (I'm seeing this with the Ubuntu gimp 2.4.5.)

...Akkana

Hi,

On Tue, 2008-07-08 at 09:56 -0600, ChadDavis wrote:

I've got a rectangle selection. Now, I am trying to do a subtractive selection within that rectangular selection, to make a sort of picture frame selection. The problem is that I'm having trouble getting the inner, substractive selection centered within the first rectangle.

When I use the ctrl key while selecting, it grows a rectangle and I can't figure out where to start the growth so it is centered. Very hard to do.

Very simple, actually. You just need to realize that it makes a difference if you press the modifier keys before you start your drag or if you press them while you are dragging. In order to subtract a centered selection you press the Ctrl key _before_ you press the mouse button. This turns the selection tool into subtract mode. Now press your mouse button in the center of the selection. If helps if you marked this point using guides beforehand. While you keep the mouse button pressed, the modifier keys get a different meaning. Ctrl centers the selection around the start point, Shift forces the aspect ratio to 1:1.

BTW, you should really upgrade to GIMP 2.4. The rectangle/ellipse selection tools are a lot easier to use there.

Sven