Exercise A.1 Figure A-13 is a special case. The simplest solution here is to select Image: Colors > Desaturate and to choose AVERAGE. For the three other figures, the best solution is to correct each color stripe by hand, using the Fuzzy Select tool to select exactly one stripe and using the Image: Colors > Hue-Saturation tool to change the color of the stripe as you wish.

Exercise A.2 First, create a new white layer and place it under the image layer. Select the top layer, and reduce its opacity to 50%. Next, add a transparent layer above this layer, and draw the polygons on it with the Pencil tool, using the key to draw straight lines. Add the text on as many new layers as necessary.

Exercise A.3 Create a new square image, for example, 1200 × 1200 pixels, with a black background. Build a circular selection of diameter 600 pixels, using the Ellipse Select tool, and press and after the initial click on the circle’s center. (Save this selection as a channel in case you lose it.) Create a transparent layer, and fill the selection with pure red. Then create another transparent layer, move the circular selection, and fill it with pure green. Do the same with a third layer but fill it with pure blue. Now set the three layers with colored circles in Addition mode and move them until you are satisfied. This process builds Figure A-36. For Figure A-39, proceed in the same way, but use white for the layer background and create the other layers in Multiply mode.

Exercise A.4 Build each figure component using Image: Colors > Components > Decompose, and choose not to decompose to layers. The corresponding images are then colorized using Image: Colors > Colorize. Finally, gather these components in an image twice the width and height of the original image.