Low level image processing is mainly concerned with extracting descriptions from images (that are usually represented as images themselves). The analysis usually does not know anything about what objects are actually in the scene, nor where the scene is relative to the observer. There may be multiple, largely independent descriptions, such as edge fragments, spots, reflectances, line fragments, etc. For example, if one was looking at an image of a coffee mug on a desk, the low level descriptions would make explicit where the mug edges were, where specular highlights were on the mug surface, what the colours on the mug were. As this description is still linked to an image, these descriptions would apply everywhere in the image, not just to the mug.

Fundamentals of Computer Vision

The Origin and Detection of Edges

Space, Frequency and Convolution