In photography “perspective” refers to the sense of width, height and depth which creates three dimensional relationships between objects in a photograph. This sense of three dimensions also includes a feeling of visual depth from the camera viewpoint into the picture distance – a feeling that you are looking at a real scene and not a two dimensional representation.
Perspective relates to visual clues that create a feeling of the three dimensionality and depth in the picture. These clues relate to common visual experiences. In particular ‘Perspective’ relates to two visual experiences:
- Relative size: Distant objects appear smaller than near objects despite larger actual measurements.
- Foreshortening: Objects, especially lines, appear increasingly compressed as distance increases along the line of sight.
In the first a person in the foreground can appear larger than a mountain in the background. The observer knows the size of near objects like a car, person, dog or tree. A full sized object with smaller ones behind gives the illusion the smaller ones are distant. We see this perspective as depth created by ‘relative size’. Objects of known size in the front helps the viewer judge the relative size of objects and the distance in the picture.
Foreshortening occurs, for example, when you look down a railway track. The lines appear compressed together with distance. The amount of compression gives you a measure of distance into the picture. Comparing other objects diminishing relative size along the lines helps add to the perception of depth.
The use of sizes and lines helps form the illusion of perspective. Knowing these basics helps you look for ways to give depth to the picture. A composition with relative size or foreshortening fools the eye. It implies three dimensions, creating depth in a photograph. This is despite being on a two dimensional medium like paper.
There are three basic types of perspective…
One-point; two-point and three point. There are three dimensions that an observer can sight along. Looking down the corner of a cube you see three edges angling away from the corner. This is three-point perspective. Standing at the corner of a building, looking either way down its walls you see two points of perspective. The lines of the building appear compressed as they distance from you. Looking along parallel lines (say, railway lines) until you see the vanishing point in the distance is an example of one-point perspective.
Convincing tricks to help the eye
Blocking – when one object blocks another out the eye assumes that there is depth because experience has shown that when you look around the blocking object you can see the other object in full a distance behind it. This convinces you that there is depth present if there are objects separated by this distance.
Relative sharpness – Photographers routinely use bokeh to help the eye focus on a specific object in the picture. The eye also uses sharpness to identify distance – things in the true distance do not have the same sharpness as objects in the foreground. Thus, slight lack of sharpness in a picture distance can trick the eye into assuming there is depth in the picture.