Sobel Operator
For the picture Our English Coasts, 1852 (Strayed Sheep) the Pre-Raphaelite painter William Holman Hunt (1827-1910) placed blocks of complementary colour next to each other. The Sobel operator applied to the painting uses a convolution matrix to find the edge of areas.
Applying a 3x3 Matrix works by averaging pixel colours with those of surrounding pixels using this process: taking pixels from left to right and from top to bottom. The resulting convolution will fill the boundary of the image with zero values or it will leave them unchanged. Applications that use the convolution technique include the creation of an emboss filter or a sharpen filter. A sharpen filter enhances edges. An emboss filter can be used for web site logos and navigation buttons. It is also possible to create filters by moving pixels from one place to another without changing their values, which results in some interesting effects. For example, suppose that the aim was to develop a puzzle game using Strayed Sheep as a template and to jumble up the sheep even further. To do that, it is necessary to implement an image filter that cuts the image into random puzzle pieces. All this is by way of explaining some underlying operations that create image filters and to develop customised versions in programming languages such as PHP.
Self-similar structures
- Cow Mutations (1987), by Tim Head in the Walker Art Gallery, Liverpool uses a jumble of images, turning the canvas into a mass of half-recognisable shapes.
- The Journal of Eugène Delacroix includes a meditation on self-similar structures and patterns in nature.
- Field's Chromatography describes how, "in landscape we see nature employing broken colours in harmonious consonance and variety".
