Perceptual Image Distortion

Patrick Teo and David Heeger, Perceptual Image Distortion, First IEEE International Conference on Image Processing, vol 2, pp 982-986, November 1994.

Model Predictions of JPEG Compressed Images

To further validate the model's performance, we applied the model to JPEG compressed images. The original image was compressed using the JPEG algorithm at different quality settings. The model was then used to predict the visibility of the distortion between each compressed image and the original.

The pairs of images on the right are images compressed using the JPEG algorithm along with the model's predictions of the amount of visible distortion when compared with the original.

The image compressed at a quality setting of 80 is virtually indistinguishable from the original. The model's prediction corroborates this observation. The average distortion value computed by the model is 1.2, which indicates that the distortion is slightly above threshold (threshold is set at 1.0). The image compressed at a quality setting of 20 is slightly deteriorated while the image compressed at a quality setting of 10 shows marked blocking artifacts. The model's predictions agree with these trends fairly well.

Click on any of the images to see them at full resolution.
[al-jpeg-80] [pdm-with-al-jpeg-80]
JPEG qual. setting = 80, RMSE = 9.5, PDM = 1.2

[al-jpeg-20] [pdm-with-al-jpeg-20]
JPEG qual. setting = 20, RMSE=11.4, PDM = 5.7

[al-jpeg-10] [pdm-with-al-jpeg-10]
JPEG qual. setting = 10, RMSE = 12.9, PDM = 9.8

Error Histograms of JPEG Compressed Images

The top graph on the right plots a histogram of the squared error differences for individual pixels. The bottom graph plots a histogram of the perceptual distortion predictions of the model for individual pixels. Both histograms have been normalized so that the vertical axis represents fractions of the total number of pixels. In the legends of both graphs, "left image" corresponds to the image compressed with a JPEG quality setting of 80; "middle image" and "right image" refer to the images compressed with JPEG quality settings of 20 and 10 respectively.

The histograms of squared error differences for the different compressed images are very similar to one another. The histograms of perceptual distortion predictions of the different compressed images are dramatically different from one another. It is clear, for example, that the model predicts that the images compressed at quality settings of 20 and 10 (the "middle" and "right" images) are more severely distorted than the image compressed at a quality setting of 80 (the "left" image).

Model predictions of visible distortion.
[sq-error-hists]

[pdm-hists]