Where part 1 gives an overall idea of the steps taken in computer-aided composition, this concluding article supplies the means, techniques and an explanation of the use of layers in the process. Once again I'll use elements of previous drawings to demonstrate.

The illustrations feature my favoured application Adobe PhotoDeluxe but any graphics program that supports layers, such as Adobe Photoshop Elements, Paint Shop Pro or Corel Draw, is equally suitable and I now use Photoshop 6 but the principles remain the same. The benefits of their use as a tool for composition are many — speed, versatility, the infinite rearranging and resizing of images, the ability to revert to earlier versions... The list is endless.

First import your line drawings or sketches that you have previously scanned (72 to 100 ppi is quite adequate) and minimise them. The images now reside in the "Open Photos" bar ready for inclusion.

Now open a new file in which to create your composition. Here it's called "comp1" and measures 11"×8", the known size of the final line drawing, and viewed at 50% size.

Now, as and when required, drag each element into your composition. Here I've dragged and dropped the two dogs and the sketch of the partial setting.

And this is where you realise that "white" and a "white background" are not the same thing!

You can clearly see the rectangle of background of the left-hand dog overlaying the setting. Also the rear of this dog is obscured by the background of the right-hand dog.

You can also see that the setting is on the bottom layer and the dogs are on the middle and top layers.

What you require is white within the body of the image and transparency outside of the image. In short, you need to delete the background. You can use the eraser or trace tool to quickly remove enough to show the layer below but you will probably save time later by removing it all now. There are a number of methods available and the one I prefer is shown here —

By now you will have realised (or already know) that each layer can be treated independently of the others. You can turn layers on or off to try out new elements that you are unsure of. You can drag layers further down the hierarchy or drag them to the top. Selected layers can be merged into a single layer. And you can, of course, move each element around the setting and even move it back and forwards by altering its size. Unless you are using Photoshop or similar with multiple undo facilities you should occasionally save the file to a new name (comp1, comp2... for example) which will allow you to return to previous attempts at any time and, if saved in their native format (.PDD or .PSD for Adobe) the layers will be preserved.