How to Use GIMP for Photo and Image Editing #2: Introduction to Layers

MozillaQuest the on-line computer magazine

January 25, 2004

Office and Productivity Software

SCO IP, SCO v Linux, & Caldera v IBM

Use GIMP rather than Photoshop and save money

Mike Angelo -- 25 January 2004 (C) -- Page 3

Article Index

Introduction

Overview of Today's GIMP Tutorial

Preview of GIMP

The Hands-On GIMP Tutorial

Getting Started
Into the Digital Darkroom
Adding a text layer
Playing with the text layer
Add a pattern layer
Alpha Channel
Create a new layer
Add the rocks
GIMP layer magic does the trick

Some Tweaks

Finished

On your own

About the Geese Photo

GIMP v Photo$hop

Adobe Photoshop & GIMP Licensing Note
Adobe Product Activation Note-

Recap and Conclusions

Resources

Books

Add a pattern layer

The water in the geese shot is very reflective, thus the bottom of the pond is obscured. So, lets add some rocks under the water. That will give the illusion of crystal clear water. It also will add some graphic interest to the background. (Actually, this is just one big excuse to show you how to add layers to images and to demonstrate some of the neat tricks you can do with layers.)

Alpha Channel

To lay the groundwork for this task, first add an alpha channel to the background (layer). To do that, toggle the combo dialog box to the Layers Dialog if you already have not done so. Then, please click on the Background-layer entry to make it the active layer.

Next, alternate-click (right-click if you are using a right-handed mouse) on the Background-layer entry in the Layers Dialog. Then in the context menu that pops up, please click on Add Alpha Channel.

The reason for adding an alpha channel is so that the initial (Background) layer will have a transparency attribute. This is necessary in order to bring that layer up from the bottom of the layers stack.

Stack is the key word here. The layers are stacked one on top of the other. An upper layer or an object on an upper layer will block out whatever is below it. If the opacity of a layer is set to 100 per-cent, then nothing below will show through. As the opacity is reduced, more of whatever is under the layer or object will show through. More about that further on.

Any layer has a foreground and a background. If the background is opaque, then an upper layer will block a lower layer as discussed above. However, if the background is transparent, then only foreground objects of the layer will block out lower layers.

For example, the text layer has a transparent background. Thus, only the content of the geese photo that is below the text layer that is directly under the text in the text layer is blocked.

Conceptually, the list of layer entries in the Layer Dialog essentially is a side view of your canvas and the layers that make up the canvas. Conceptually, the canvas view is a top-view of the layers that make up the canvas. Thus, when you look at the canvass, conceptually you are looking down at and through the stack of layers.

Create a new layer

To create a new layer, please click on the New Layer icon in the Layers Dialog. The New Layer icon is the left-most icon at the bottom of the Layers Dialog. (Figure 4, on page 2.)

That pops-up the New Layer Dialog. (Figure 5, below.)

You can name the new layer whatever you like. In this example it gets named Pattern. The new Layer Width and Height should be the same as the photo dimensions. In this example, that's 345 x 142 pixels. Pick Transparent for the Layer Fill Type. Then, Click OK.

Now, the Layers Dialog should show three layer entries, the original Background layer, the text layer, and the new Pattern layer. Please see Figure 6, below.

Figure 5. The GIMP New Layer Dialog. (Screen shot of GIMP version 1.3 running on SUSE Linux 9.0 and the KDE desktop for Linux. Please see text for an explanation.)

Add the rocks

Here you can toggle the combo dialog box to the Pattern Grid Dialog (the paint bucket icon).

However in Figure 6, two separate Pattern Grid Dialogs were opened to help explain this step of the tutorial. (To do that, use Dialogs > Create New Dock > Brushes, Patterns, & Gradients ... and then click on the Pattern Grid icon on the Icon Bar at the top of that new combo Brushes, Patterns, & Gradients dialog.)

The Patterns Dialog at the lower-right of Figure 6 shows the default size of the pattern samples. The Patterns Dialog at the upper-left of Figure 6 shows the pattern samples in Extra Large size.

To change the pattern sample sizes, alternate-click on the Pattern Grid icon on the Icon Bar at the top of the combo Brushes, Patterns, & Gradients dialog. Then on the context menu that pops up click Preview Size and then click on your size choice.

Now let's add the rocks to the Pattern Layer of the photo. First, select the rocks pattern. That's the sample that is second in from the left in the top row of pattern samples in the upper-left dialog of Figure 6. Click on the Rock Pattern Sample to select it.

You are all set to add the rocks to the photo. In order to make sure the rocks get onto the Pattern Layer, please go to the Layers Dialog (bottom-left in Figure 6) and click on the Pattern-Layer entry to highlight it.

Next, click on Edit > Fill with Pattern. (Please see Figure 7, below.)

Bang! The rocks now are in your photo/image. (Please see Figure 8, on page 4.)

Whoa, what happened to the photo of the geese? It's a picture of rocks in Figure 8, not geese.

Have no fear. The GIMP's powerful Layer Tools are here.

Figure 6. Screen shot showing the addition of a new layer (arbitrarily named the Pattern layer) where a pattern will be added to the photograph. Please see text for an explanation. (GIMP version 1.3 running on SUSE Linux 9.0 and the KDE desktop for Linux. Geese photo by Mike Angelo)

GIMP layer magic does the trick

Please notice in the Layers Dialog in Figure 8, on page 4, that the Pattern-Layer entry is highlighted -- and also that it is in between the text-layer entry at the top and the Background-layer entry at the bottom. Thus, the rocks cover the geese in the Background layer but the text covers the rocks -- as shown in the Figure 8 canvas window in the upper right.

Now is the time for two neat GIMP layer-magic tricks. The first is to move the rocks under the geese. The second is to decrease the opacity of the geese photo so that the rocks can be seen under the water of the geese photo -- but not so much of a decrease as to let the rocks show through the more dense geese.

Here is how to do these GIMP layer-magic tricks.

First, make sure the Pattern-Layer entry in the Layers Dialog is highlighted. Then click on the down-arrow at the bottom of the Layers Dialog to move the Pattern-Layer entry under the Background-Layer entry (the geese). (Please see Figure 8, on page 4.)

Next, highlight the Background-Layer entry in the Layers Dialog and then set the opacity to .64. You can use the opacity slider for that. (Please see Figure 9, on page 4.)

Now in our example, the geese appear to be on top of the rocks. (Please see Figure 9.) However, at that .64 opacity setting the water is almost invisible.

So, let's slide the opacity up to .84. Also, you can play around with the opacity slider to find the opacity that you like best. Figure 10, on page 4, shows the geese photo with the .84 opacity setting for the geese (Background layer).

Figure 7. The GIMP Fill with Pattern choice selected in the Edit Menu. (Screen shot of GIMP version 1.3 running on SUSE Linux 9.0 and the KDE desktop for Linux. Please see text for an explanation.)

See Some Tweaks on Page 4 ----->

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