Adaptive histogram-based video contrast enhancement
First Claim
1. A contrast enhancement system, comprising:
- a histogram updater that is configured to provide a current-frame cumulative histogram based on a received image frame, to divide the current-frame histogram into regions, to determine an arithmetic mean for at least two of the regions of the current-frame histogram, and to calculate variances for each of the determined arithmetic means;
a weighting factor calculator that is configured to calculate weighting factors based on the calculated variances; and
an equalizer that is configured to transform pixel values of the received image frame using the weighting factors and statistics from a previous-frame cumulative histogram.
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Abstract
The adaptive contrast enhancer uses an adaptive histogram equalization-based approach to improve contrast in a video signal. For each video frame, the histogram of the pixel luminance values is calculated. The calculated histogram is divided into three regions that are equalized independently of the other. The equalized values are averaged with the original pixel values with a weighting factor that depends on the shape of the histogram. The weighting factors can be also chosen differently for the three regions to enhance the darker regions more than the brighter ones. The statistics calculated from one frame are used to enhance the next frame such that frame buffers are not required. Many of the calculations are done in the inactive time between two frames.
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Citations
20 Claims
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1. A contrast enhancement system, comprising:
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a histogram updater that is configured to provide a current-frame cumulative histogram based on a received image frame, to divide the current-frame histogram into regions, to determine an arithmetic mean for at least two of the regions of the current-frame histogram, and to calculate variances for each of the determined arithmetic means; a weighting factor calculator that is configured to calculate weighting factors based on the calculated variances; and an equalizer that is configured to transform pixel values of the received image frame using the weighting factors and statistics from a previous-frame cumulative histogram. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for enhancing contrast of an image, comprising:
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generating a current-frame cumulative histogram based on a received image frame; dividing the current-frame histogram into regions; determining an arithmetic mean for at least two of the regions of the current-frame histogram; calculating variances for each of the determined arithmetic means; calculating weighting factors based on the calculated variances; and transforming pixel values of the received image frame using the weighting factors and statistics from a previous-frame cumulative histogram. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification