In reacting or responding to an object, we are only able to do so when we have identified what it is, recognized its main features and bring to mind its meaning. This is simply ‘object recognition’. When a lion approaches us, we realise through prior knowledge that the animal is known to be ferocious, dangerous and sometimes doesn’t hesitate to kill. With this information, we are able to make instant decisions as to the next course of action. A meal at a dinner table tells us it is edible and we can approach it. This ‘spatial localisation’ is the establishing of where objects are in the surrounding space and time and is also an important aspect of survival. Another factor necessary for survival is ‘perceptual constancy’. This is when objects, although the eyes perceive them to be in motion, are kept constant in terms of appearance. Object recognition, spatial localisation and perceptual constancy are the three main characteristics of perception.
One theory that aims to explain object recognition and constancy is Marr’s theory which concerns itself with visual processing. It is also called the computational approach which involves taking two-dimensional images and extracting valuable three-dimensional information from them. This theory requires examining the levels of grey in an image, creating a rough sketch, then a 2.5D sketch and representing the image as a 3D model. Marr’s model of object recognition is concerned with drafting out representations of objects with an increasing amount of information. The first step in this representation is creating the raw or full primal sketch. Raw primal sketches contain data regarding the light intensity variations of a shape or scene. A full primal sketch makes use of this data to determine how many outlines and objects are contained within the scene. The light intensity changes provided in the raw primal sketch gives the level of grey representation contained within the pixels of the image.
Computation on the properties shape can begin when it has become coloured i.e. detached from the background. .