Journal ArticleDOI
Contrast in complex images.
TLDR
A definition of local band-limited contrast in images is proposed that assigns a contrast value to every point in the image as a function of the spatial frequency band and is helpful in understanding the effects of image-processing algorithms on the perceived contrast.Abstract:
The physical contrast of simple images such as sinusoidal gratings or a single patch of light on a uniform background is well defined and agrees with the perceived contrast, but this is not so for complex images. Most definitions assign a single contrast value to the whole image, but perceived contrast may vary greatly across the image. Human contrast sensitivity is a function of spatial frequency; therefore the spatial frequency content of an image should be considered in the definition of contrast. In this paper a definition of local band-limited contrast in images is proposed that assigns a contrast value to every point in the image as a function of the spatial frequency band. For each frequency band, the contrast is defined as the ratio of the bandpass-filtered image at the frequency to the low-pass image filtered to an octave below the same frequency (local luminance mean). This definition raises important implications regarding the perception of contrast in complex images and is helpful in understanding the effects of image-processing algorithms on the perceived contrast. A pyramidal image-contrast structure based on this definition is useful in simulating nonlinear, threshold characteristics of spatial vision in both normal observers and the visually impaired.read more
Citations
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Journal ArticleDOI
Shift in spatial scale in identifying crowded letters.
Susana T. L. Chung,Bosco S. Tjan +1 more
TL;DR: In this paper, the authors measured contrast thresholds for identifying the middle target letters in trigrams, for a range of spatial frequencies, letter separations and letter sizes, at the fovea and 5 degrees eccentricity.
Journal ArticleDOI
Analyzing the influence of contrast in large-scale recognition of natural images
TL;DR: A new contrast measure, called Harris Points Measured Contrast (HPMC), is introduced, which assigns values of contrast in a more consistent form to images, according to their recognition rate than other global and local compared contrast analysis methods.
Journal ArticleDOI
New contrast enhancement approach for dark images with non-uniform illumination
TL;DR: This work proposes a method which deals with ‘YCbCr’ model, as by using this color model the authors can separately use luminance part ‘Y’ of the image by using a newly developed sigmoid function.
Mesure du contraste local dans les images, Application à la mesure de distance de visibilité par caméra embarquée Measurement of local contrast in images, Application to the measurement of visibility distance through use of an onboard camera
TL;DR: A partir de la definition de la distance de visibilite meteorologique, Nous conduit a proposer une methode generique de mesure de the distance of visibile atmospherique par camera embarquee a bord d'un vehicule as discussed by the authors.
Journal ArticleDOI
Infrared (IR) thermography-based quantitative parameters to predict the risk of post-operative cancerous breast resection flap necrosis
Ashish Saxena,Eddie Y. K. Ng,Vignesh Raman,Muhammad Syarifuddin Bin Mohamed Hamli,Mateusz Moderhak,Szymon Kolacz,Jerzy Jankau +6 more
TL;DR: To predict the post-operative necrosis risk (within 24 h), novel passive and active dynamic thermography-based quantitative parameters were tested and resulted in a highest sensitivity, specificity, and accuracy for the passive thermography examination performed just after the surgery.
References
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Chapter 9 Visual adaptation and retinal gain controls
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Feature Detection in Human Vision: A Phase-Dependent Energy Model
TL;DR: A simple and biologically plausible model of how mammalian visual systems could detect and identify features in an image is presented and it is suggested that the points in a waveform that have unique perceptual significance as ‘lines’ and ‘edges’ are the points where the Fourier components of the waveform come into phase with each other.
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Contrast constancy: deblurring in human vision by spatial frequency channels.
Mark A. Georgeson,G.D. Sullivan +1 more
TL;DR: It is argued that spatial frequency channels in the visual cortex are organized to compensate for earlier attenuation, and achieves a dramatic 'deblurring' of the image, and optimizes the clarity of vision.