Abstract
Psychophysical scaling is commonly based on the assumption that the overall quality of images is based on the
assessment of individual attributes which the observer is able to recognise and separate, i.e. sharpness, contrast, etc.
However, the assessment of individual attributes is a subject of debate, since they are unlikely to be independent from
each other.
This paper presents an experiment that was carried to derive individual perceptual attribute interval scales from overall
image quality assessments, therefore examine the weight of each individual attribute to the overall perceived quality. A
psychophysical experiment was taken by fourteen observers. Thirty two original images were manipulated by adjusting
three physical parameters that altered image blur, noise and contrast. The data were then arranged by permutation, where
ratings for each individual attribute were averaged to examine the variation of ratings in other attributes.
The results confirmed that one JND of added noise and one JND of added blurring reduced image quality more than did
one JND in contrast change. Furthermore, they indicated that the range of distortion that was introduced by blurring
covered the entire image quality scale but the ranges of added noise and contrast adjustments were too small for
investigating the consequences in the full range of image quality. There were several interesting tradeoffs between noise,
blur and changes in contrast. Further work on the effect of (test) scene content was carried out to objectively reveal
which types of scenes were significantly affected by changes in each attribute.
