1. Image quality measures
Pasi Fränti

2. Pixelwise measures

3. Classical measures Mean squared error (MSE):
Peak Signal to Noise ratio (PSNR):
Original pixel values are xi and distorted xi. Maximum pixel value is 255.

4. Blockwise measure

5. Blockwise distortion measure Signal Processing: Image Communication, 13 (2), 89-98, 1998

6. Three quality factors Contrast errors: Structural errors:
Quantization errors:

7. Weighting the factors Weighted sum: Scaling function:
Scales the values approximately to the range 0, 1.
Negative values are rounded to zero.

8. Test images
Lena (512512)
Airplane (512512)
Bridge (256256)

9. Test arrangements Image samples: Offset quality photographs
Viewing conditions:
Normal office environment
Viewing distance:
Free of choice for the observer
Time of evaluation:
Unlimited
Number of observers:
15-39
Grading:
Extended MOS scale (0-10).

10. Visual examples
JPEG (1.0)
BTC QT

11. JPEG
BTC QT
Contrast:
Structural:
Quantization:

12. Scatter of the quality grades

13. Quality grades

14. Correlation to subjective quality

15. Conclusions Blockwise measure instead of pixelwise like MSE or PSNR
Correlates better to subjective quality
Old method but worth to study further:
Extension to Multi-scale resolution
Study with newer image datasets
Compare to SSIM1 and RF2
1 W. Zhou, A.C. Bovik, H.R. Sheikh, E.P. Simoncelli Image quality assesment: from error visibility to structure similarity IEEE Trans. on Image Processing, 13 (4), , 2004.
2 A. Mahmoudi-Aznaveh, A. Mansouri, F. Torkamani-Azar, and M. Eslami Image Quality Measurement Besides Distortion Type Classifying Optical Review, 16 (1), 30-34, 2009.