One of the main problems with the creation of bitmap based materials is getting them to look as though they repeat or tile seamlessly across a rendered surface. This tutorial explains the various ways by which this can be achieved.
By way of an illustration of the problem, look at the two bitmap tiles illustrated on the right. They are both 100px by 100px. They are both JPEGs and superficially they both look similar. However, when used as a material, one of them displays obvious seams while the other doesn't. The bluewave1.jpg image was created simply by scribbling with the Airbrush Tool in Photoshop. The bluewave2.jpg image has been tweaked so that it will tile seamlessly. The rendered result of each of these two images are illustrated below. The material based on the bluewave1.jpg image is shown on the left and the material based on the bluewave2.jpg material is shown on the right. The bluewave1 material displays obvious vertical seams. In this case, the horizontal seams aren't too obvious but that's more a case of luck than judgement. What we need is a sure fire method of creating a material that can be tiled without showing any seams.
