Picture Simulation of Contrast Sensitivity in Organic and Functional Amblyopia

1996

The appearance of four different images from three different distances was simulated by using the individual contrast sensitivity functions (CSF's) of normally sighted observers. The simulations were generated by using the observers' CSF's as a threshold in a pyramidal vision model of band-limited local contrast [J. Opt. Soc. Am A 7, 2030 (1990)]. Simulations based on CSF's obtained in an orientation discrimination task underestimated the observer's sensitivity in discriminating the images. Simulations based on CSF's obtained in a detection task provided a good estimate of observer's performance. The testing method was shown to be sensitive enough to be affected by the high-frequency residual, which is frequently ignored in visual models and simulations. An image-dependence effect found when the high-frequency residual was present was eliminated when the residual artifact was removed. The simulations based on the pyramidal vision model accurately predicted the distance at which they were discriminated from the original image, and thus this model may also serve as the basis for image-quality metrics. The testing method developed can also be used to determine the type of CSF that best represents observer performance in a task.

Section: Evaluating the Model By Using Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Test of a model of foveal vision by using simulations

1996

“…Simulating the appearance of a scene or an image to an observer is a useful design and analysis tool. Such pictorial representations have been attempted by many investigators over the years in a variety of applications in vision science [1][2][3][4] and engineering. [5][6][7] Such simulations are frequently generated within the context of a computational vision model.…”

Section: Introductionmentioning

confidence: 99%

Contrast sensitivity function and image discrimination

2001

A previous study tested the validity of simulations of the appearance of a natural image (from different observation distances) generated by using a visual model and contrast sensitivity functions of the individual observers [J. Opt. Soc. Am. A 13, 1131 (1996)]. Deleting image spatial-frequency components that should be undetectable made the simulations indistinguishable from the original images at distances larger than the simulated distance. The simulated observation distance accurately predicted the distance at which the simulated image could be discriminated from the original image. Owing to the 1/f characteristic of natural images' spatial spectra, the individual contrast sensitivity functions (CSF's) used in the simulations of the previous study were actually tested only over a narrow range of retinal spatial frequencies. To test the CSF's over a wide range of frequencies, the same simulations and testing procedure were applied to five contrast versions of the images (10-300%). This provides a stronger test of the model, of the simulations, and specifically of the CSF's used. The relevant CSF for a discrimination task was found to be obtained by using 1-octave Gabor stimuli measured in a contrast detection task. The relevant CSF data had to be measured over a range of observation distances, owing to limitations of the displays.

“…Computational vision models have been used to predict the discrimination and the appearance of images and scenes in a variety of experimental contexts. [1][2][3][4][5][6][7] One such multiscale model of spatial vision was used to calculate local band-limited contrast in complex images. 8 This contrast measure along with the observers' contrast sensitivity functions (CSF's) were used to simulate the appearance of images to observers with both normal 8 and low 7 vision.…”

Section: Introductionmentioning

confidence: 99%

Discrimination of wide-field images as a test of a peripheral-vision model

Geri

2001

In order to test a model of peripheral vision, various contrast sensitivity functions (CSF's) and fundamental eccentricity constants (FEC's) [see J. Opt. Soc. Am. A 8, 1762 (1991)] were applied to real-world, wide-field (6.4 degrees-32 degrees eccentricity) images. The FEC is used to model the change in contrast sensitivity as a function of retinal eccentricity. The processed test images were tested perceptually by determining the threshold FEC for which the observers could discriminate the test images from the original image. It was expected that higher CSF sensitivity would be associated with higher FEC's; and in fact, for images processed with low-pass (variable-window stimuli) CSF's, the threshold FEC's were larger for the higher-sensitivity (pattern-detection) CSF than for the lower-sensitivity (orientation detection) CSF. When two higher-sensitivity CSF's were compared, the bandpass (constant-window stimuli) CSF resulted in essentially the same FEC threshold as did the low-pass (variable-window stimuli) CSF. The fact that the FEC compensated for complex differences in the form of the CSF suggested that the discrimination task was mediated by a limited range of spatial frequencies over which the two CSF's were similar. Image contrast was then varied in order to extend the range of spatial frequencies tested. The FEC's estimated with the lower-contrast test images were unchanged for test images obtained with the high-sensitivity, bandpass CSF but increased for test images obtained with the high-sensitivity, low-pass CSF. These results suggest that peripheral contrast sensitivity as used in the present discrimination task is based on a high-sensitivity, bandpass CSF. The peripheral-vision model validated by the present analysis has practical applications in the evaluation of wide-field simulator images as well as area-of-interest or other foveating systems.