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HowTo: Create Artistic Backgrounds using the Gimp - Part 3

Novell Cool Solutions: Feature
By Stomfi

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Posted: 23 Dec 2004

This is last part of the series, "Create Artistic Backgrounds using the Gimp". It shows the basics of creating and using layer channels and masks, and using filters and script-fu scripts in an artistic way. When you have completed these three how tos you will be able to create your own screen wallpaper, as well as birthday and Christmas cards.

StomfiLearning to use Linux at Home and Work
Welcome to my ongoing series of HowTo articles designed to help Linux newbies get comfortable with Linux. Before trying any of these HowTos, take a few minutes to study the prerequisites so you can hit the ground running.

This HowTo is about using the Gimp to manipulate pictures to create an original that can be used as desktop backgrounds. In Part 1 & Part 2 we used simple methods for selection tools, layers, copy and paste, changing the size and transparency of floating layers, and anchoring. In part 3 we are going to use masks, channels and filters to make more modifications to our screen background picture. The Gimp can do a lot more than is described in this simple HowTo, but here you will learn some of the basic and simple ways of doing things.

In the previous parts we saw that when selections are made, the effect we apply only gets done in the selected parts of the picture.

Sometimes, when working on a picture, we may like to go back to a previous selection, and do more work on the same area, or even put the selection shape into another area. You can use the channel tools to save selections and recall them.


This is the picture I made in Part 2. And here is the new selection.


Right click on the selection, and click "Select" - "Save to Channel" like this.


The channel dialog looks like this:

Double click on the Selection Mask Copy. Change its name to "bluerect".

In the picture Click "Select" - "None" from the menu. Now we shall resurrect the selection which we can do at any time. In the "Layers" dialog, right click on the saved channel, which I called "bluerect". Click on "Channel to Selection".

You will see the selection reappear in your picture. You can save as many selections as you like, giving each one a meaningful name so you can remember what they were for.

Now that we've had a play with channels it's time to move on to some mask work and make changes to the picture.

Change the "Layers" dialog back to show the layers. Click on the picture. Click "Edit" - "Copy" from the menu. Click "Edit" - "Paste as New". You will get a new picture with a blue rectangle. Minimise this for now as we will use it in a bit. We are now going to save the current selection, by floating it onto a new layer, which can then be manipulated as a separate picture.

Right click "Select" - "Float" . Move to the "Layers" dialog where you will see the floating selection.

Click new layer icon bottom right of the Layers dialog and the floating selection will turn into a new layer. Double click the layer and give it a meaningful name. e.g. "Fade Out".

We will now perform some simple mask magic. Right click the new layer and click "Add Layer Mask". The "Add Mask Options" dialog box will pop up.

Select "Black" for full transparency and click OK.

A layer mask will appear next to the layer, A mask is a special tool which allows you to change the transparency of part or all of a layer. It uses black and white and shades of grey to do this. Remember black is transparent, white is opaque, shades of grey are in between.

For this trick to work, make sure the foreground colour is black, and the background, a light shade of grey for partial transparency. If they are not, use the colour select icons as shown, to change them. If you don't know how to do this the next picture will show you.

This is the Gimp main menu.

You use File to select the first file. Xtns you can explore by yourself. Help is for the help I don't give you. The icons represent the tool box. Most of these are also in the screen menus, but sometimes you may want to use these. Like if you click the magnifier, you can draw the area you want to magnify.

The bottom right area displays the current brush/pencil size and shape, the pattern and the blend.

The left area selects the colours. This yellow bit is the tool tip.

This is the colour selector you see after you have double clicked on one of the two large colour squares.

I have clicked my mouse in the V bar to select a grey colour.

Click OK when satisfied. You can always undo the blend and change the grey to something more suitable.

When you've set the colours, select the "Blend tool" from the Gimp menu. That's the greenish square on the fourth line of the tool box as shown above.

Left press and drag the mouse across the selected area in the picture.

The result will fade from full opacity to partial transparency. It doesn't look too good as there is nothing underneath the transparency.

We will try the same trick again but this time we will paste another layer underneath this one so that we can go from full opacity to full transparency exposing the under layer. This is where that Paste as New picture gets used.

Click "Edit" - "Undo" to remove the blend.

Use the magnifier tool to zoom into the area we are working on. Leave at least a 10mm border on the zoom area.

We need to pick a light colour from this picture to use to paint the new under layer.

Use the colour picker from the Gimp menu. That's the one that looks like an eye dropper.

Pick a light colour from the zoomed picture. Mine is a light blue.

Go to the Layers dialog and click the new layer icon.

Click the eye against the main picture so it disappears from view.

Maximise the Paste as New picture and click inside the rectangle to make it the active picture.

Use the bucket fill tool from the Gimp menu and fill the rectangle with the light colour.

Click "Edit" - "Copy" in its menu and minimise this picture.

Click inside the picture to select the main picture again, and make sure your new layer is high lighted.

Click "Edit" "Paste" in the main picture menu.

Your "Layer" dialog should look like this:

And your picture like this:

You can see that the pasted layer is not quite in the right place. We put the mouse into the blue square and hold down the left button and move it until it is. When it is OK, release the button, move the mouse outside the selection, where the cursor changes to an anchor and left click to anchor it in place on the layer. You can also do this from the menu in Layers.

Lower the new layer and make it active. Now there is a new blue rectangle between the masked layer and the main picture. Thus:

Now change the foreground colour back to black. Click the mask layer square in the Layers dialog to make it active. Choose the blend tool, and repeat the blend press and drag action in the picture. Yeah, that looks much better.

You can try changing the white background colour to another shade of grey, do an undo and repeat the blend to see different results.

Save the work by going to the Layer dialog. High light the main picture layer. Right click and click "Merge visible layers". Click OK in the pop up window. All the layers will turn into one.

In the picture, click "View" - "Zoom" - "Zoom to fit Window".

Another simple trick to do with layer masks is making only part of a layer visible or invisible. This is similar to the blend except we use a colour to paint onto the layer mask where we want things to hide or show. Using this effect we can put two pictures together exposing bits of each to make a new composite.


Select an area where you want to paste a new picture and float the layer to a new layer like we did before. With the Gimp menu "File" menu, open the picture you are going to paste as the bottom layer of the composite, copy it to the clipboard, close or minimize the source picture. Click in the main picture and make the new layer active and paste and scale the floating paste, then anchor it. Hey that was pretty good. Does your Layer dialog look like mine.

Now repeat the whole procedure with the picture that you want part of on top of this one. Your Layer dialog should look like this now, with two extra layers.


Make a white mask layer for your new upper layer. Your layer dialog should look like this.


Click on the white layer mask square. That's the square to the right of the layer square. A white border will mark that it is active. I have turned off the eye in the main picture to make it easier to work on the target layers. I have also zoomed in.

We are going to paint or draw in black on this layer in the main picture to expose the parts of the lower picture we want showing.

Choose a brush size to do the main work and start drawing. This is part way through the process.


When you get this far you probably want to choose a smaller brush size to finish off.

You get the idea. When you are finished click the eye in the layer dialog on the main picture. Make this the active layer and merge visible layers.

This has been a basic layer channel and mask primer, which should help you create some interesting art works for your Xmas and birthday cards.

If these two layers had been swapped in order, you could have made a black mask on the upper layer, and painted in white to block out the bits you didn't want.

The last area of interest in this final Gimp HowTo is a quick look at Filters and Script-Fus.

Zoom the full picture, and select a new area to work on.

Click "Filters" - and click one you want to try. Usually a pop up will appear with some parameters you can change. Here are some I tried, with the pop ups and results.



The next lot are Script-Fus. These are made with scripts that apply combinations of filters, a bit like a Macro. Often, Gimp users send them in. When you run them you will see information pop ups about which filter is currently running.

I have done two. "Predator" like in the movie, and 'Coffee Stain" which went over the whole picture, and created several new layers. By clicking off the eye on each of the new layers you can see which one you like and delete the rest. You can also scale, move and do other things to the layer before you merge it.

My picture looks a real mess now, but I hope you've been able to do better yourselves.

There are system wallpapers which are used as screen backgrounds in "/usr/share/wallpapers"

There is probably somewhere on the web, that you can get your best efforts included in this collection.

If you make a smaller picture which can be tiled, there is a filter in the map collection called make seamless, which you can use so that there are no obvious joins at the tile edges.

If you see a small area of your picture that you want to use as a brush, so you can draw, paint or even use it as a stamp, there is a "Script-Fu" - "Selection" - "To Brush" for doing just that. There is also a "To Image" in the same menu which is a lot easier than doing "Edit" - "Copy" - Edit" - "Paste as New". And you can use it as a pattern in "To Pattern".

You are on your own now. Have a lot of Fun with the Gimp and send Santa a Gimp made Xmas card this year, I look forward to seeing some of your clever wallpapers in a future update of the wallpaper package.

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