Overview
Selections are a powerful way of isolating parts of an image, so you can localize edits to only affect those areas.They can be used to cut out regions of an image, or limit the effect of transforms or filters to a particular area. Selections are drawn as a dotted black and white boundary, but in actual fact selections are not purely a matter of ‘inside’ and ‘outside’. Selections often have soft areas that are only partially selected. For example this allows the effect of a filter to smoothly fade out at the edge of the selection. This partially selected region is called a ‘feather’.
Creating Selections
There are several ways within Pixeluvo of creating selections. The simplest selection method of all is to select the entire image. You can do this from the menus at the top by selecting Select->Select All, or with the shortcut Ctrl+A. If you do this you will now see a dotted black and white border moving around the image. This is showing that the whole image is now selected. The Copy and Cut operations in the Edit menu operate on the current selection, so in order to copy the whole image to the clipboard, you can do Select->Select All followed by Edit->Copy. The selected region of the current layer will now be in the clipboard and can be pasted in other applications or within Pixeluvo (for example into a new document).
To clear the selection use Select->Select None or the shortcut Ctrl+D.
You can also create selections using the various selection tools. The Box Select tool allows you to quickly select rectangular regions of an image, and can be activated by pressing ‘m’. Similarly, the Ellipse Select tool creates elliptical selections. The Lasso Select tool allows you to draw both freehand selections and polygonal selections composed of straight edges. Finally the Magic Wand tool allows you to easily select contiguous areas of similar color.
Selections can also be created from the alpha channel of layers and from layer masks by Ctrl+Clicking on the layer or mask preview in the layers panel, more detail on that below.
Adjusting Selections
Each of the selection tools allows you to add or subtract from the current selection, as well as simply replacing it with a new selection. This allows you to build up more complex selections piece by piece. From the Select menu there are also options to invert the selection, expand or shrink the selection by a number of pixels and to apply a feather.
Feathering the selection is such a common operation that it is worth learning the shortcut Crtl+F. This brings up a dialog where you can set the radius of the feather. Think of this as blurring the selection by that amount. You can preview the resulting selection as a black and white mask by selecting ‘Show Mask’ in this dialog. White areas are 100% selected, black areas are 0% selected, and grey values represent a partial selection of some amount. Toggle the ‘Show Preview’ option to display the mask with and without the feather applied.
Selections and Masks
When you have a selection active, all editing operations are restricted to just that region. For example, if you use the paintbrush tool whilst there is an active selection then none of the paint will appear outside of the selected region. Similarly you can transform the selected area using any of the operations in the Edit->Transform menu without changing the unselected areas of the image.
This also applies to all of the color correction filters and effects. The filters will only affect the selected areas of the image. The selection is in effect acting as a mask in exactly the same way that masks on layers limit which parts of a layer are visible. Because of this notion of the selection acting as a mask, Pixeluvo makes it easy to create a layer mask from a selection and vice versa. Use Layer->Add Mask->Reveal Selection to create a layer mask from the selection (you can use Hide Selection to create an inverted mask). To create a selection from a layer mask simply hold Control and click on the layer mask preview in the layers panel. To create a selection from the alpha channel of an image Control+Click on the layer preview.