Assessment of visually lossless irreversible image compression: comparison of three methods by using an image-comparison workstation.
OBJECTIVE
To determine the degree of irreversible image compression detectable in conservative viewing conditions.


METHODS
An image-comparison workstation, which alternately displayed two registered and magnified versions of an image, was used to study observer detection of image degradation introduced by irreversible compression. Five observers evaluated 20 16-bit posteroanterior digital chest radiographs compressed with Joint Photographic Experts Group (JPEG) or wavelet-based trellis-coded quantization (WTCQ) algorithms at compression ratios of 8:1-128:1 and x2 magnification by using (a) traditional two-alternative forced choice; (b) original-revealed two-alternative forced choice, in which the noncompressed image is identified to the observer; and (c) a resolution-metric method of matching test images to degraded reference images.


RESULTS
The visually lossless threshold was between 8:1 and 16:1 for four observers. JPEG compression resulted in performance as good as that with WTCQ compression at these ratios. The original-revealed forced-choice method was faster and as sensitive as the two-alternative forced-choice method. The resolution-metric results were robust and provided information on performance above visually lossless levels.


CONCLUSIONS
The image-comparison workstation is a versatile tool for comparative assessment of image quality. At x2 magnification, images compressed with either JPEG or WTCQ algorithms were indistinguishable from unaltered original images for most observers at compression ratios between 8:1 and 16:1, indicating that 10:1 compression is acceptable for primary image interpretation.
Slone
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RM
Mallinckrodt Institute of Radiology, Washington University School of Medicine, Barnes-Jewish Hospital, Box 8131, 510 S Kingshighway Blvd, St Louis, MO 63110, USA. sloner@mir.wustl.edu
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Whiting
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Muka
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Rubin
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Pilgram
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Kohm
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Young
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Hendrickson
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D000465:Algorithms; D016477:Artifacts; D003199:Computer Systems; D003626:Data Display; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008171:Lung Diseases / Q000000981:diagnostic imaging; D017563:Lung Diseases, Interstitial / Q000000981:diagnostic imaging; D008297:Male; D008477:Mediastinal Diseases / Q000000981:diagnostic imaging; D015588:Observer Variation; D011014:Pneumonia / Q000000981:diagnostic imaging; D019736:Prostheses and Implants; D011856:Radiographic Image Enhancement; D011858:Radiographic Magnification; D013902:Radiography, Thoracic; D012680:Sensitivity and Specificity; D012984:Software