GIMP's Ellipse Select Tool is a relatively simple way to select pixels, but the various options make it rather more flexible than it may seem at first glance.
Selection tools allow you operate upon specific areas of an image without having any effect on immediately surrounding pixels. The Tool Options dialog offers a range of other tools that allow the way the tool operates to be amended.
Mode
The default setting is Replace the current selection which means that whenever you draw a new selection, any existing selections are canceled. However, by using the other selection modes--namely Add to the current selection, Subtract from the current selection and Intersect with the current selection--you can start to create surprisingly complex shapes built out of multiple ellipses, even with holes removed.
Antialiasing
This makes the outlines of the selection seem smoother and is visible when the selection is filled with a solid color.
Feather Edges
This allows edges to be softened so that the selection fades. When selected, a slider is displayed to allow the degree of feathering to be easily adjusted.
Expand from Center
This makes placing the center of a selection on a specific point very easy, rather than drawing a selection first and then trying to position its center accurately.
Fixed
This option constrains the Ellipse Select Tool in one of four ways
- Aspect Ratio – you can restrict the proportions of the ellipse; for example, 1:1 would produce a perfect circle
- Width – the ellipse will always be the width specified in the field below the Fixed checkbox, but the height can be set freely
- Height – basically the same as Width, but the height will always be the same and the width is varied
- Size – the exact height and width of the ellipse can be specified before drawing the selection
Position
This option can allow you to fine tune a selection and place it accurately with the option to move the selection by just one pixel at a time.
Size
Works much the same as the Position option but allows you to vary the dimensions of the ellipse by one pixel at a time for accurate ellipse selections.
Highlight
Only the selection that is currently being drawn will be highlighted and the rest of the image, including existing selections, will be grayed out.
Guides
You can select from several Guides options that can help you to place ellipse selections more accurately upon an image.
Auto Shrink
This reduces the size of an ellipse selection so that there are no background colored or transparent pixels between the boundary of the selection and any colored pixels within the original selection. If you click the Shrink merged checkbox, this tool will operate on all layers rather than just the active one.
When using GIMP on a regular basis to achieve a few types of effects, it can be very easy to overlook the full power and flexibility of the Ellipse Select Tool, but any time that you spend exploring the Tool Options dialog will almost certainly pay you back in the long run.
