Electronic image processing with automatic color correction
First Claim
1. A method of preparing an image of an original, comprising the steps of scanning said original in each of the primary colors red, green and blue;
- generating a luminance value and at least one related chrominance value for each of a multiplicity of regions of said original based on the scanning step, said luminance values spanning of predetermined range;
dividing said range into a plurality of segments so that different ones of said luminance and chrominance values lie within different segments;
classifying the regions having luminance and chrominance values within said segments as color dominant or color nondominant;
calculating at least one representative value for each of selected segments based on corresponding chrominance values, the calculating step including assigning different weights to dominant and nondominant regions in such a manner that the representative value for each selected segment represents an overall color cast for selected regions of the respective segment;
adjusting each of said of said representative values with reference to the gray point to generate a respective adjusted value; and
establishing a correction plot for each of the primary colors based on the pairs of representative and adjusted values.
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Abstract
A colored original is scanned point-by-point and density values are generated for each point in the primary colors red, green and blue. The points are divided into groups and the density values for each primary color are averaged over the respective groups. The averaged density values for each group are transformed into a set of converted values including a luminance value as well as first and second chrominance values. The range spanned by the luminance values is divided into segments and each set is assigned to a respective segment. The sets are classified as color dominant or color nondominant by comparing the saturation value of each set with a threshold value. For each, segment the first and second chrominance values of the nondominant sets are respectively added to yield first and second sums. The first and second sums are shifted relative to the gray point to generate corrected first and second sums. Each pair of uncorrected first and second sums is converted into uncorrected red, green and blue density values whereas corrected density values are obtained from the corresponding pair of corrected first and second sums. For each primary color, the corresponding uncorrected and corrected density values define a point in a coordinate system of uncorrected density versus corrected density. By plotting the points from the various segments, a correction curve can be established for each primary color.
39 Citations
20 Claims
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1. A method of preparing an image of an original, comprising the steps of scanning said original in each of the primary colors red, green and blue;
- generating a luminance value and at least one related chrominance value for each of a multiplicity of regions of said original based on the scanning step, said luminance values spanning of predetermined range;
dividing said range into a plurality of segments so that different ones of said luminance and chrominance values lie within different segments;
classifying the regions having luminance and chrominance values within said segments as color dominant or color nondominant;
calculating at least one representative value for each of selected segments based on corresponding chrominance values, the calculating step including assigning different weights to dominant and nondominant regions in such a manner that the representative value for each selected segment represents an overall color cast for selected regions of the respective segment;
adjusting each of said of said representative values with reference to the gray point to generate a respective adjusted value; and
establishing a correction plot for each of the primary colors based on the pairs of representative and adjusted values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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17. The method of claim 1, wherein each of said plots comprises a series of connected straight line segments;
- and further comprising the step of smoothing said plots.
- generating a luminance value and at least one related chrominance value for each of a multiplicity of regions of said original based on the scanning step, said luminance values spanning of predetermined range;
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18. An apparatus for preparing an image of an original, comprising means for scanning the original in the three primary colors red, green and blue;
- and data processing means operatively associated with said scanning means and including means for generating a luminance value and at least one related chrominance value for each of a multiplicity of regions of the original with resulting establishment of a predetermined range of luminance values, means for dividing the predetermined range into a plurality of segments such that different ones of said luminance and chrominance values lie in different segments, means for classifying the regions having luminance and chrominance values within the segments as color dominant or color nondominant, means for calculating at least one representative value for each of selected segments based on corresponding chrominance values by assigning different weights to dominant and nondominant regions in such a manner that each representative value represents an overall color cast for selected regions of the respective segment, means for adjusting each representative value with reference to the gray point so as to generate a respective adjusted value, and means for establishing a correction plot for each of the primary colors from the paris of representative and adjusted values.
- View Dependent Claims (19, 20)
Specification