Image processing algorithm for characterization of uniformity of printed images
First Claim
1. An image quality analysis System for determination color non-uniformities in an image output device, comprising:
- a test pattern pertinent to image quality determination;
a scanner that scans a hardcopy test image, which has been generated by the output device based on the test pattern, to form a digital raster image; and
an image quality analysis module that receives the digital raster image, distinguishes one or more test targets from the digital raster image and detects color non-uniformities, uniformities, and performs image quality analysis on the test budgets to obtain results quantifying image quality, wherein the image quality analysis module includes means for categorizing detected color non-uniformities as either structured or non-structured variances, the means for categorizing including;
means for converting the image to a complex valued image represented as an amplitude and phase; and
means for generating a binary image mask from the complex valued image by dividing a frequency range of the complex valued image into at least a low range and a high range, wherein pixels of the image in the low range arc categorized as non-structured variances and pixels of the image in the high range are compared against average amplitude and standard deviation and categorized as structured variances if the comparison deviates by more than a predetermined threshold.
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Abstract
This invention specifically covers one of the many image quality (IQ) metrics that can be part of an overall image quality analysis engine. The specific problem with image quality addressed with this metric is that of a region of a printed (or copied) image, which was intended to have a uniform color, but which shows visible color variations. The color variation can have many different forms, both with respect to the type of color difference and with respect to the spatial nature of the non-uniformities. The image quality analysis system readily distinguishes between non-uniformities in the following different categories, including: (a) amplitude modulated cluster dot halftone patterns; (b) frequency modulated halftone patterns (e.g., stochastic screens); (c) irregular two-dimensional variations from noise; (d) isolated (non-periodic) one-dimensional streaks; (e) periodic, one-dimensional bands; and (f) two-dimensional periodic variations (Moire). The results from the image quality analysis can then be used as a basis for diagnosing machine problems.
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Citations
22 Claims
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1. An image quality analysis System for determination color non-uniformities in an image output device, comprising:
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a test pattern pertinent to image quality determination;
a scanner that scans a hardcopy test image, which has been generated by the output device based on the test pattern, to form a digital raster image; and
an image quality analysis module that receives the digital raster image, distinguishes one or more test targets from the digital raster image and detects color non-uniformities, uniformities, and performs image quality analysis on the test budgets to obtain results quantifying image quality, wherein the image quality analysis module includes means for categorizing detected color non-uniformities as either structured or non-structured variances, the means for categorizing including;
means for converting the image to a complex valued image represented as an amplitude and phase; and
means for generating a binary image mask from the complex valued image by dividing a frequency range of the complex valued image into at least a low range and a high range, wherein pixels of the image in the low range arc categorized as non-structured variances and pixels of the image in the high range are compared against average amplitude and standard deviation and categorized as structured variances if the comparison deviates by more than a predetermined threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 22)
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11. A method of performing image quality analysis on an image output device having an output station that generates a hardcopy image from a digital image, the method comprising:
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generating a hardcopy image output from the image output device based on a predetermined test pattern;
scanning the hardcopy image using a scanner to form a digital raster image;
performing image quality analysis on test targets of the image to determine color non-uniformities;
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categorizing determined color non-uniformities into structured and non-structured variances, wherein the categorizing includes;
converting the image to a complex valued image represented as an amplitude and phase;
generating a binary image mask from the complex valued image by dividing a frequency range of the complex valued image into at least a low range and a high range;
categorizing pixels in the low range as non-structured variances; and
comparing pixels in the high range with average amplitude and standard deviation and categorizing pixels as structured variances if the comparison deviates by more than a predetermined threshold. - View Dependent Claims (12, 13, 14, 17)
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15. A method of performing image quality analysis on an image output device having an output station that generates a hardcopy image from a digital image, the method comprising:
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generating a hardcopy image output from the image output device based on a predetermined test pattern;
scanning the hardcopy image output from the image output device based on a predetermined test pattern;
scanning the hardcopy image using a scanner to form a digital raster image having one or more test targets;
performing image quality analysis on the test targets to determine color non-uniformities;
categorizing determined color non-uniformities into structured and non-structured variances;
after categorizing the determined color non-uniformities, applying a human visual filter to the image; and
separating the human visual filtered image into structured and non-structured components. - View Dependent Claims (16)
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18. A method of performing image quality analysis on an image output device having an output station that generates a hardcopy image from a digital image, the method comprising:
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generating a hardcopy image output from the image output device based on a predetermined test pattern;
scanning the hardcopy image using a scanner to form a digital raster image;
performing image quality analysis on test targets of the image to determine color non-uniformities by converting the digital raster image from a color image to a monochrome image representing luminance and calculating average amplitude and standard deviation for pixels of the monochrome image over a predefined frequency range;
categorizing determined color non-uniformities into structured and non-structured variances; and
categorizing individual pixels as structured or non-structured based on a comparison of the individual pixel with the calculated standard deviation. - View Dependent Claims (19, 20, 21)
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Specification