Image quality

[2]: vii  Objective and subjective methods aren't necessarily consistent or accurate between each other: a human viewer might perceive stark differences in quality in a set of images where a computer algorithm might not.

Subjective methods for image quality assessment belong to the larger area of psychophysics research, a field that studies the relationship between physical stimulus and human perceptions.

These methods can be classified depending on the availability of the source and test images: Since visual perception can be affected by environmental and viewing conditions, the International Telecommunication Union produced a set of recommendations for standardized testing methods for subjective image quality assessment.

[4] Wang & Bovik (2006) classify the objective methods with the following criteria: (a) the availability of an original image; (b) on the basis of their application scopes and (c) on the model of a Human Visual System simulation to assess quality.

[5] Keelan (2002) classifies the methods based on (a) direct experimental measurements; (b) system modeling and (c) visual assessment against calibrated standards.

[6]: 173 Image quality metrics can also be classified in terms of measuring only one specific type of degradation (e.g., blurring, blocking, or ringing), or taking into account all possible signal distortions, that is, multiple kinds of artifacts.