3 Working with Layers and Selections
In the lesson, we will learn:
- About layers and the Layer Window
- How to manipulate layers
- How to select text and graphic regions
- How to copy and cut text and graphics
3.1 Using the Layer Window
Layers are a fundemental building blocks of an image. They allow you to work on individual components of an image while leaving the rest of the image alone. When stacked on top of one another, layers are combined to produce a finished image. The contents of layers higher in the stack block out the contents of layers beneath them. As a result, transparent layers containing text and graphics are the most popular layers to stack. Typically, the lowest layer contains a solid color or background image that covers the entire book cover.
The Layer Window shows you the layers that have been defined in an image and the order in which they’re stacked. You can use commands in the Layer Window and the buttons at the bottom of the window to manipulate the layers.
Use the File->Open menu item to open the book cover you saved in the previous lesson. It should contain two layers: one layer named “Background” which contains the image and a text layer containing the title of the book and your author name. The name of the text layer will be the text it contains. Since the text layer is above the image layer, its contents block out the contents of the image directly below the text (the contents of the text layer other than the text is transparent).
By the way, transparency is displayed in the GIMP as a checker board of light and dark gray squares.
When adding a new graphical or textual component to a book cover, create it on a new layer so that you can individually manipulate and position it.
3.2 Selecting a Layer
To work with a layer, you must first select it in the Layers Window. The selected layer is displayed as light gray in the window. To select a layer, click on on it’s name. The operation you perform in the image manipulation window will then effect only the contents of the selected layer.
Note that the number one reason that things go wrong when working with the GIMP is that you don’t have the correct layer selected when working on an image. If you want to modify the text of your book cover, first click on the text layer in the Layers window. If you try to select the text box while the image layer is selected, nothing will happen. If you want to work on the image, first click on the “Background” layer.
3.3 Adding and Duplicating a Layer
To add a layer above the current layer, click on the button in the lower left corner of the Layers Window (it looks like a piece of paper with the top right corner folded down). Remember, by placing your mouse pointer above a button without clicking it a tooltip will appear explaining the purpose of the button.
The “Create a New Layer” dialog box will be displayed. In this dialog box you can name the new layer and choose whether it should be filled with the forground color (“Black”), the background color (“White”), White, or it should be transparent. In most cases you will want a transparent layer so that only the things you place on the layer will block the contents of lower layers. Click the “OK” button to create the layer.
Use the “Duplicate Layer” button, the fourth button over at the bottom of the Layers Window, to duplicate the current layer.
3.4 Raising and Lowering a Layer
Because the contents of higher layers block the contents of lower layers, layer order is important. Use the up and down arrows at the bottom of the Layers Window to move the current layer up and down through the layer stack.
3.5 Making a Layer Invisible and Visible
Sometimes it’s handy to temporarily make a layer invisible to see what lies beneath it. Click the eye to the left of a layer to temporarilly hide and then show the contents of the layer. Note that the layer still exists, its contents just can’t be seen.
3.6 Deleting a Layer
Click the garbage can in the lower right corner of the Layers Window to delete the current layer. Note that you can use Edit->Undo to undo this operation.
3.7 Merging Two Layers
Sometimes it’s useful to deal with the contents of two layers as a single element. In this case, the layers should be merged.
First, use the up and down arrows to insure that the two layers to be merged are next to each other. RIGHT click on the layer on top and select “Merge Down” from the popup menu. The two layers will be merged to produce a single layer.
3.8 Image, Text, and Floating Layers
As you work with the GIMP, you’ll come across three types of layers that display themselves differently in the Layers Window.
Image layers are layers that contain graphic elements. They display themselves in the Layers Window as a thumbnail of the image contents in the box to the left of the layer name.
Text layers are layers that contain text that can be modified using the Text Tool. They display themselves with the letter “A” in the box to the left of the layer name.
Floating layers are selections that have not yet been anchored onto a layer. These appear in the middle of a Cut & Paste or Copy & Paste operation. Be sure to anchor your layers before performing further work by clicking on the anchor symbol at the bottom of the Layers window.
3.9 Selecting All and None
In the remainder of this lesson, we’ll learn how to select all or a portion of a layer for Cut & Paste or Copy & Paste operations. In a later lesson, we’ll use selection with the Bucket Tool to create colored boxes.
Before selecting anything, insure that the correct layer is selected in the layers Window.
To select everything on a layer, use the Select->All menu item. A boarder, known as marching ants, will surround your selection.
To turn off a selection (when no longer needed), use the Select->None menu item.
3.10 Using Rectangular Selection
To select a rectangular portion of a layer, use the Rectangle Select Tool located in the upper left corner of the Toolbox Window. After selecting this tool, your mouser cursor will turn to an “+” in the image manipulation window. To use it, position the plus sign to the upper left of the selection, hold down your left mouse button, and drag your mouse to the lower right corner of the selection. A green/purple box will be used to show your selection.
When you release your left mouse button, marching ants will be used to show the boundaries of your selection. You can move your mouse pointer over any side or corner of the selection and click and drag your mouse to increase or decrease the size of the selection. You can click and drag in the center of the selection to move it.
3.11 Using Elliptical Selection
Similar to the rectangular selection tool but creates an eliptical selection. The button to enable this tool is directly to the right of the Rectangle Selection Tool. Use it to produce circular selections.
3.12 Using Free Selection
The Free Select Tool, the lasso to the right of the Elipse Select Tool, can be used in two ways to perform freeform selection.
First, you can hold your left mouse button down while dragging the mouse pointer around the image manipulation window to create your selection. Second, you can repeatedly click your left mouse button to create a series of straight lines to form your selection. You can alternately use both methods to create your selection. To close your selection, move your mouse to the start point of the selection while holding your mouse down or click over your start point.
Use free selection to select complex shapes. In a later lesson, we’ll learn to use the erase tool to clean up our selection.
3.13 Using Color Selection
Color selection allows you to select everything on the layer of a particular color. To use it, select the tool (second from the right on the top row) and click on a color. Marching ants will appear around all occurances of that color on the layer.
Note that you can drag the “Threshold:” slider to the right to select colors that are farther and farther from being close to the color you select. A better way to add close colors to the selection is outlined in the following section.
3.14 Adding and Subtracting Selection
You can use any of the above selection methods to add to an existing selection by holding down the Shift key on your keyboard before performing the selection. You can remove portions of a selection by holding down the Ctrl key and doing the same.
The addition selection technique is most useful when performing color selection. In this case, choose the color selection tool, hold down the Shift key, and continue to add colors to your selection by clicking on colored pixels in the image manipulation window. If you accidently select a color you don’t want, use the Edit->Undo menu item to remove the selection.
If color selection results in selecting a portion of the image you didn’t want to select (e.g. you’re selecting a flower and some words get selected), you can hold down the Cntrl key and select the portions of the selection you want to remove from the current selection (e.g. using rectanbular selection).
Using selection additional and subtraction, you can use all of the techniques outlined in this section to build a complex selection through several operations.
3.15 Inverting Your Selection
Sometimes its easier to select what you don’t want then it is to select what you do want. In these cases, select what you don’t want and invert your selection. For example, if you want to select a complex image on a solid white background, it’s easy to select the solid white background with one Select by Color Tool click and invert the selection to select everything not currently selected.
Use the Select->Invert menu item to unselect everything selected and select everything not selected. Note that you can use invertion in the middle of building a complex selection using multiple selection and deselection steps.
3.16 Moving a Layer
Since we’ll be following the convention of placing a single graphical element on seperate transparent layers, we can move graphical elements around our book cover by moving the layer. Use the Move Tool, second column far right in the Toolbox, to move a graphical element.
To use this tool, select the correct layer, click and hold down your left mouse button over the graphical element, and drag it to its new location. Release your mouse button when you’re done.
Don’t worry if the outline of your layer overlaps the borders of your image, it will be cropped to fit.
3.17 Copy & Paste
Once you’ve selected a portion of an image, you can make a copy of it by selecting the Edit->Copy menu item, moving to a new layer by adding a layer or selecting a layer in the Layer Window, and using Edit->Paste to paste the selection into the new layer.
3.18 Cut & Paste
Cut & Paste is like Copy & Paste above, except that you remove the selected region from the source layer and paste it to its destination. Use this technique to move and image or colored box around the image.
3.19 Copying from One Image to Another
Note that you can select and copy a region of an image or text from one image to another by opening the image you want to copy from using File->Open, creating your selection in the opened image manipulation window, executing Edit->Copy from that window, then selecting a different image manipulation window in which to perform you Edit->Paste.
When you select one of multiple open image manipulation windows by click your left mouse button somewhere in the window, or on its border, the Layers Window changes to show you the layers in the selected image manipulation window. Working with multiple images at a time is key to creating a complex book cover.
Use this techinque to copy images from multiple sources onto a single book cover. Remember to always paste to a new transparent layer.
Project 3.1: Modify Your First Book Cover
Modify your first book cover by removing the author name following the book title and reentering each as a seperate text layer. To add a new text layer, simply select the Text Tool (“A”) in the Toolbox Window and click somewhere on your image outside the existing text box. Being sure to select the correct layer for modification, change your author name to a smaller font. Now move the title and the author name seperately, after changing to the appropriate layers, to place them in the best locations on your cover.
### End of Lesson Copyright (c) 2011, Brian Jackson