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Results

  Table 4.1.2 combines both sets of scores for each picture used in the experiment. All figures are measure in the units of JPEG Compression index. Table 4.1.2 shows the improvement in compression ratio when different cut-off points are used; a JPEG compression index of 75 was used as the baseline. Finally table 4.1.2 shows the probabilities and significance that the scores generated across subjects and between pictures are draw from the same population. Clearly, in all cases but one the images can be said to have different JPDs.

   

1st and 2nd Set Combined (JPEG index)
mean sd wse wie
face 27.13 8.37 8.22 13.65
tree 18.10 10.18 7.48 18.43
map 25.06 8.92 9.85 18.31
room 31.40 8.92 6.02 10.63
all 25.42 8.48 7.89 12.95
wse=within subject mean squared err
wie=within image mean squared error
Table 2: Mean Scores Of Both Sets For All Subjects And All Pictures.

   

mean+2*sd 42.38 57%
mean+sd 33.90 78%
mean 25.42 113%
Table 3: Mean Compression Ratios For Meaningful Cut-Off Points

   

sets P of Similarity Significance
face-tree 3.26e-09 High
face-map 0.0724 None
face-room 4.18e-05 High
tree-map 2.41e-05 High
tree-room 5.08e-10 High
map-oom 1.21e-06 High
Table 4: Results of pair wise t-test for each picture pair


next up previous
Next: Image Quality Choices Up: Perceptual Limits on JPEGs Previous: The Subjects:

Malcolm McIlhagga
Thursday June 11 16:17:19 BST 1998