Automated tone correction apparatus and method using filtered histogram equalization
First Claim
Patent Images
1. A method for improving tone of an original image comprising steps of:
- generating a pixel representation of the original image;
filtering the pixel representation with a filter having a response peak near a spatial frequency at which the human eye is highly sensitive;
converting pixel tones to emphasize patterns in the original image having tone values which vary at a spatial frequency at which the human eye is highly sensitive, thereby generating an improved image.
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Abstract
An image processing system redistributes image luminance values in an image represented in u'"'"'v'"'"'L* space to achieve a near-optimal fit of luminance data to available dynamic range and to enhance the shape and detail of the resultant image. Redistribution may be accomplished by passing the image through a filter having a peak response at a spatial frequency at which the human eye is highly sensitive, and then equalizing a cumulative histogram of filtered pixels. An image may be transformed to compensate for tone compression which accompanies printing processes.
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Citations
26 Claims
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1. A method for improving tone of an original image comprising steps of:
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generating a pixel representation of the original image; filtering the pixel representation with a filter having a response peak near a spatial frequency at which the human eye is highly sensitive; converting pixel tones to emphasize patterns in the original image having tone values which vary at a spatial frequency at which the human eye is highly sensitive, thereby generating an improved image. - View Dependent Claims (2, 3, 4)
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5. A method for improving tone of an original image comprising steps of:
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generating a pixel representation of the original image; filtering the pixel representation with a filter having a response peak near a spatial frequency at which the human is highly sensitive; computing an effect value for pixels based on filtered pixel values; generating a first histogram from pixels having effect values greater than a threshold; and generating a second histogram from pixels having effect values less than the threshold; converting pixel tones in accordance with the first and second histograms, thereby generating an improved image. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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13. A method for improving tone of an original image comprising the steps of:
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generating a pixel representation of the original image; modifying pixel tones; and modifying pixel chrominance in accordance with the amount of tone modification, there by generating a tone-modified image with colorfulness compensation and wherein such tone modifying step includes; (i) filtering the pixel representation with a filter having a frequency repsonse peak near a spatial frequency at which the human eye is highly sensitive; and (ii) converting tones of pixels to emphasize patterns in the original image having tone values which vary at a spatial frequency at which the human eye is highly sensitive.
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14. A method for improving tone of an original image and compensating for tone alteration imposed by a limited output gamut comprising steps of:
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generating a pixel representation of the original image; storing the pixel representation in memory of a programmed computer; modifying the pixel representation at least in part according to a tonal transform producing colors outside the gamut; and modifying the pixel representation at least in part according to a compensation transform which modifies tone in relation to an amount of tone alteration imposed by the limited output gamut, thereby generating an improved image. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method for improving tone of an original image and compensating for a limited output gamut comprising steps of:
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generating a pixel representation of the original image; generating an initial tonal transform that emphasizes patterns in the original image having tone values which vary at a spatial frequency at which the human eye is highly sensitive, displaying the pixel representation to an operator; receiving from the operator at least one command to alter a tone selected from the displayed image; generating a manual transform which further maps image tones according to the received command while preserving the character of the initial tonal transform; and modifying the pixel representation according to the initial and manual transforms, thereby generating an improved image.
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Specification