Hi,

How do I get a selection of the entire inside of an outline of a circle? For example, I have a transparent background, and I draw a circle in black (it looks like this " O ", minus the quotes). I use the "Select Region By Color" and click on the black outline of the circle. If I click Select -> Invert, I get the outside of the circle, as well as the inside. My ultimate goal is to put a gradient inside the circle, but I have to get inside first :-)

Thank you.

-- __________________________
DJ

I would suggest putting your circle on a separte transparent later, then filling it with black.
Then right-click on layer, alpha-to-selection, then shrink by one, then create anew transparent layer, then put the gradient on that layer, which will be the inner part of the circle.

On 5/21/07, rcook@pcug.org.au wrote:

Hi,

How do I get a selection of the entire inside of an outline of a circle? For example, I have a transparent background, and I draw a circle in black (it looks like this " O ", minus the quotes). I use the "Select Region By Color" and click on the black outline of the circle. If I click Select -> Invert, I get the outside of the circle, as well as the inside. My ultimate goal is to put a gradient inside the circle, but I have to get inside first :-)

Thank you.

-- __________________________
DJ

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DJ wrote:

Hi,

How do I get a selection of the entire inside of an outline of a circle? For example, I have a transparent background, and I draw a circle in black (it looks like this " O ", minus the quotes)

How do you draw the circle in the first place? Are you using the circular selection tool & stroke the selection? In this case, the selection remains after you have drawn the circle, and you can simply apply a gradient of your choice inside the circle.

But what I personally noticed (i just tried it myself right now) is the bad anti-aliasing of the circle. I tried several tools, but the results are far from satisfying. My suggestion would be, to draw the circle in a vector program like Inkscape, where the anti-aliasing is much better, and then import it into Gimp as a PNG. Or does any- body else know how to draw a smooth circle using the Gimp?

Claus

On 5/22/07, Claus Cyrny wrote:

DJ wrote:

Hi,

How do I get a selection of the entire inside of an outline of a circle? For example, I have a transparent background, and I draw a circle in black (it looks like this " O ", minus the quotes)

How do you draw the circle in the first place? Are you using the circular selection tool & stroke the selection? In this case, the selection remains after you have drawn the circle, and you can simply apply a gradient of your choice inside the circle.

But what I personally noticed (i just tried it myself right now) is the bad anti-aliasing of the circle. I tried several tools, but the results are far from satisfying. My suggestion would be, to draw the circle in a vector program like Inkscape, where the anti-aliasing is much better, and then import it into Gimp as a PNG. Or does any- body else know how to draw a smooth circle using the Gimp?

Claus

Drawing a circle in Inkscape will not improve it's quality. The gimp quality is about the maximum, and you'll find that inkscape provides pretty much the same quality.
When you want to shrink the selection, on the other hand -- inkscape can certainly do that well. In gimp it's relatively complex, involving converting the shrunken selection to a path and then the path back to a selection.
Personally, I have that sort of procedure set up as a plugin, and it uses potrace as a backend rather than the lower-quality 'autotrace' software that is used by the selection-to-path plugin.

David Gowers wrote:

Drawing a circle in Inkscape will not improve it's quality. The gimp quality is about the maximum, and you'll find that inkscape provides pretty much the same quality.

I have to disagree with you. I noticed that the anti-aliasing in the Gimp is by far not as good as in Inkscape, and I can post some screenshots to prove my point. As I wrote, I tried several ways to improve the anti-aliasing of the
circle in the Gimp, but not to much avail.

Claus

On 5/22/07, Claus Cyrny wrote:

David Gowers wrote:

Drawing a circle in Inkscape will not improve it's quality. The gimp quality is about the maximum, and you'll find that inkscape provides pretty much the same quality.

I have to disagree with you. I noticed that the anti-aliasing in the Gimp is by far not as good as in Inkscape, and I can post some screenshots to prove my point. As I wrote, I tried several ways to improve the anti-aliasing of the
circle in the Gimp, but not to much avail.

And I have to disagree with you :) Are you zoomed in past 100%? I can't think of any other reason your circle in GIMP should be jagged.

Chris

On 5/21/07, DJ wrote:

Hi,

How do I get a selection of the entire inside of an outline of a circle? For example, I have a transparent background, and I draw a circle in black (it looks like this " O ", minus the quotes). I use the "Select Region By Color" and click on the black outline of the circle. If I click Select -> Invert, I get the outside of the circle, as well as the inside. My ultimate goal is to put a gradient inside the circle, but I have to get inside first :-)

Thank you.

You've already gotten some good suggestions, but I would use the "fuzzy select" tool to select the center of the circle.

HTH, Chris

Chris Mohler wrote:

On 5/22/07, Claus Cyrny wrote:

David Gowers wrote:

Drawing a circle in Inkscape will not improve it's quality. The gimp quality is about the maximum, and you'll find that inkscape provides pretty much the same quality.

I have to disagree with you. I noticed that the anti-aliasing in the Gimp is by far not as good as in Inkscape, and I can post some screenshots to prove my point. As I wrote, I tried several ways to improve the anti-aliasing of the
circle in the Gimp, but not to much avail.

And I have to disagree with you :) Are you zoomed in past 100%? I can't think of any other reason your circle in GIMP should be jagged.

I wonder what I'm doing wrong! :-( Here's an example of what I tried (Gimp 2.2.8/Ubuntu "Breezy"/24-bit color depth):
http://home.arcor.de/ccyrny/downloads/circles_rgb.png

The "jaggies" remain. :-(

How do you achieve getting a smooth circle? I checked both anti-aliasing and feather (3.0) in the selection tool. The zoom factor was always 100%.

Claus

On 5/22/07, Claus Cyrny wrote:
[...]

I wonder what I'm doing wrong! :-( Here's an example of what I tried (Gimp 2.2.8/Ubuntu "Breezy"/24-bit color depth):

http://home.arcor.de/ccyrny/downloads/circles_rgb.png

The "jaggies" remain. :-(

How do you achieve getting a smooth circle? I checked both anti-aliasing and feather (3.0) in the selection tool. The zoom factor was always 100%.

Strange - I must never have stroked a selection in GIMP, because it *is* very jagged. I'm going to search the bugzilla, but this is a workaround:
1. make elliptical selection
2. fill with black
3. selection->shrink->enter width of desired stroke in pixels 4. clear

HTH,
Chris

Chris Mohler (cr33dog@gmail.com) wrote:

On 5/22/07, Claus Cyrny wrote:
[...]

I wonder what I'm doing wrong! :-( Here's an example of what I tried (Gimp 2.2.8/Ubuntu "Breezy"/24-bit color depth):

http://home.arcor.de/ccyrny/downloads/circles_rgb.png

The "jaggies" remain. :-(

How do you achieve getting a smooth circle? I checked both anti-aliasing and feather (3.0) in the selection tool. The zoom factor was always 100%.

Strange - I must never have stroked a selection in GIMP, because it *is* very jagged. I'm going to search the bugzilla,

If you want I can go into all the technical details, why this is that way. It is not pretty, but there is no easy solution - we have to somehow deal with the fact, that a selection is not a vector-based shape and stroking has to have something to follow.

Another workaround is to convert the selection into a path and then stroke the path, this should also give better (but not perfect) results.

Relevant Bugzilla entry: http://bugzilla.gnome.org/show_bug.cgi?id=50730

Bye, Simon

here is a sample comparing 2 400 pixel circles created with Chris's instructions

www.dottedi.biz/codesamples/images/400x400_circle.gif www.dottedi.biz/codesamples/images/400x400_circle.png

1. make elliptical selection (select elliptical region) 1.1. hold the shift key down as you drag and this will force a perfect circle 2. fill with black
3. selection->shrink->enter width of desired stroke in pixels 4. clear

the .gif version is expectedly jagged, the .png is acceptably smooth.

Chris Mohler wrote:

On 5/22/07, Claus Cyrny wrote:
[...]

I wonder what I'm doing wrong! :-( Here's an example of what I tried (Gimp 2.2.8/Ubuntu "Breezy"/24-bit color depth):

http://home.arcor.de/ccyrny/downloads/circles_rgb.png

The "jaggies" remain. :-(

How do you achieve getting a smooth circle? I checked both anti-aliasing and feather (3.0) in the selection tool. The zoom factor was always 100%.

Strange - I must never have stroked a selection in GIMP, because it *is* very jagged. I'm going to search the bugzilla, but this is a workaround:
1. make elliptical selection
2. fill with black
3. selection->shrink->enter width of desired stroke in pixels 4. clear

HTH,
Chris

that's the technique i've been using :)

On 5/22/07, Bob Meetin wrote:

here is a sample comparing 2 400 pixel circles created with Chris's instructions

www.dottedi.biz/codesamples/images/400x400_circle.gif www.dottedi.biz/codesamples/images/400x400_circle.png

1. make elliptical selection (select elliptical region) 1.1. hold the shift key down as you drag and this will force a perfect circle 2. fill with black
3. selection->shrink->enter width of desired stroke in pixels 4. clear

the .gif version is expectedly jagged, the .png is acceptably smooth.

Chris Mohler wrote:

On 5/22/07, Claus Cyrny wrote:
[...]

I wonder what I'm doing wrong! :-( Here's an example of what I tried (Gimp 2.2.8/Ubuntu "Breezy"/24-bit color depth):

http://home.arcor.de/ccyrny/downloads/circles_rgb.png

The "jaggies" remain. :-(

How do you achieve getting a smooth circle? I checked both anti-aliasing and feather (3.0) in the selection tool. The zoom factor was always 100%.

Strange - I must never have stroked a selection in GIMP, because it *is* very jagged. I'm going to search the bugzilla, but this is a workaround:
1. make elliptical selection
2. fill with black
3. selection->shrink->enter width of desired stroke in pixels 4. clear

HTH,
Chris
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