title: Visual search performance of patients with vision impairment: effect of JPEG image enhancement.
abstract: OBJECTIVE
  To measure natural image search performance in patients with central vision impairment. To evaluate the performance effect for a JPEG based image enhancement technique using the visual search task.
  
  
  METHODS
  One hundred and fifty JPEG images were presented on a touch screen monitor in either an enhanced or original version to 19 patients (visual acuity 0.4-1.2 logMAR, 6/15 to 6/90, 20/50 to 20/300) and seven normally sighted controls (visual acuity -0.12 to 0.1 logMAR, 6/4.5 to 6/7.5, 20/15 to 20/25). Each image fell into one of three categories: faces, indoors, and collections. The enhancement was realized by moderately boosting a mid-range spatial frequency band in the discrete cosine transform (DCT) coefficients of the image luminance component. Participants pointed to an object in a picture that matched a given target displayed at the upper-left corner of the monitor. Search performance was quantified by the percentage of correct responses, the median search time of correct responses, and an 'integrated performance' measure - the area under the curve of cumulative correct response rate over search time.
  
  
  RESULTS
  Patients were able to perform the search tasks but their performance was substantially worse than the controls. Search performances for the three image categories were significantly different (p <= 0.001) for all the participants, with searching for faces being the most difficult. When search time and correct response were analyzed separately, the effect of enhancement led to increase in one measure but decrease in another for many patients. Using the integrated performance, it was found that search performance declined with decrease in acuity (p = 0.005). An improvement with enhancement was found mainly for the patients whose acuity ranged from 0.4 to 0.8 logMAR (6/15 to 6/38, 20/50 to 20/125). Enhancement conferred a small but significant improvement in integrated performance for indoor and collection images (p = 0.025) in the patients.
  
  
  CONCLUSIONS
  Search performance for natural images can be measured in patients with impaired vision to evaluate the effect of image enhancement. Patients with moderate vision loss might benefit from the moderate level of enhancement used here.
authors.affiliation: Schepens Eye Research Institute, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA. gang.luo@schepens.harvard.edu
authors.forename: Gang
authors.initials: G
authors.lastname: Luo
authors.forename: PremNandhini
authors.initials: P
authors.lastname: Satgunam
authors.forename: Eli
authors.initials: E
authors.lastname: Peli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016288:Computer Terminals; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D013647:Task Performance and Analysis; D014786:Vision Disorders / Q000503:physiopathology*; D014796:Visual Perception / Q000502:physiology*