Learning objectives

When you have completed this session, you should be able to

• list the selecting tools,
• make a selection.

Select tools

Perhaps the most important component of pixel-graphic image editing is the application of select tools. Selection means that some points of a picture are set for working on them. Thus all the following operations will have an effect on the points selected in the picture.

The simplest select tools are simple geometric formations, rectangles, ellipses. For instant when selecting a rectangle a rectangular area of the picture is set and all operation we do with the picture will have an effect only on this area. If, for example we draw with the Painbrush we can only do that within this area. In other words the points of the picture not set are locked up from editing.

A very important fact must be mentioned yet. When a setting is in effect and some operations are being done in the setting; that will only influence the active layer. The setting does not change the fact that work can only be done on the active layer. So selecting the layer defines the active layer and within that setting defines those points of the picture where editing will have the influence.

Settings can be used for many things. This can be best experimented in practice. Settings and layers can be used together very effectively.

Also there is a possibility to select some of the picture partially. This means that editing has only a moderate effect on these points. The value of the selection can be varied between 0 and 100%. 100% is a fully selected point and editing has a full effect on it. 0% means an unselected (protected) point so the operations do not have any effect on it. Editing has a 50% effect on a 50% selected point (for example if a pixel is colored into red that will be semi-transparent).

In Gimp the selected parts are bordered with blinking intermittent dividing line. This is often called marching ants due to the fact that the effect similar to them. With this technique partial selection cannot be represented. This can be displayed with other technique which will be mentioned later in the chapter about Masks.

Discontinuing selection can be done with the SHIFT+CTRL+A key combination.

Simple selections, forcing keys

Simplest selections can be created with the simple application of selection tools. While drawing the selected area with forcing keys the shape of the selection can be modified. Pressing the SHIFT button while drawing a rectangle results a square. Doing the same when drawing an ellipse results a circle. When CTRL button is pressed the increasing of the selected area is centralized.

To select irregular areas use the Free Select tool. To select coherent areas use the Fuzzy Select tool.

Selecting single color areas, the Fuzzy Select

Fuzzy Select gives the ability to select single color areas. Click with the magic wand somewhere in the picture. Gimp will scan the picture and selects the pixels identical with the selected one.

In respect to this threshold is important. It tells how much the difference can be between the pixel selected and the pixels found after scanning. It is a number between 0 and 255; so this value is based on the values of the individual components of colors. In case of 0 only pixels having the exactly same color are selected.

Another important option of Fuzzy Select is Sample Merge. If this box is active the selection is extended to the pixels in every layer.

Transforming selection

When transforming selections we can think of two things:

• transform only the selection or
• transform the selection and its contents too.

In order to transform a selection chose the proper transforming tool after selecting. At properties where Competence can be adjusted a small switch, called Transforming Selection can be found. If it is active, not the layer but the selection will be transformed. Otherwise transforming selections are similar to transforming layers.

If we intend to transform the selection together with its contents switch for transforming the layer.

Moving selected area

When moving selected areas also two things are possible. Moving only the selected area or moving its contents too.

In the first case activate the selecting tool, select an area which is not empty and select the moving tool’s switch for transforming selection; than move the selected area.

In the second case the simplest method is to move the area after selection with the selecting tool itself. (The more difficult way is giving the suspended command of Selection and move by activating moving tool.)

Selections and Layers

It is very useful to make new layers from selections and select non-transparent pixels respectively. Just an example to demonstrate it:

We design a web page and we would like to create a nice background and place texts and buttons on it. The background of the buttons and the texts must be identical with the background of the web page. If the text or the buttons are created on the background layer we may damage our background, especially when the result is not nice and we want to undo the original background. That will be a difficult task. For this reason we select a part of the background and create a layer from this. We create the texts on this layer and the buttons on another one. If we spoil something now we just simply delete the layer and the background is not damaged. Another advantage is that the layer can be moved freely; so if positioning is not correct it can be modified easily.

Selection can be discontinued with the key combination of SHIFT+CTRL+A (or with the discontinue command of Selection menu).

Creating layers from selections

Make a selection. Activate the layer from which the new layer is to be created.

There are two ways to create a new layer. One possibility is to copy the selected area of the active layer into a new layer. This way the active layer is unchanged and a new layer is made.

The other way is to cut the selected area of the active layer and make a layer from it. This way the original layer will be modified too. The selected part will be deleted.

Copy can be done with CTRL+C key combination; cutting can be done with CTRL+X key combination. Get a new layer but do not cease the selection. Than give the Local Paste command from Edit menu. The selection can be discontinued now even twice.

The new layer is always created above the active layer and this is the one that becomes active.

Selecting Layers

It is often useful to select the non-transparent points of a layer. For instance when a filter is used on the layer and the effect is only needed on non-transparent pixels. For this reason these pixels have to be selected out.

This can be done by activating the layer which has the contents we intend to select and in the Layer menu at Transparency we chose the command: Add to Selection.

These steps can be repeated for several different layers so the selection can be extended.

The Subtract from Selection and Intersect with Selection commands can also be used in order not only to add to the existing selection but subtract the contents of the layer or create a segment.