Patent ID: 8326028

Claim:
A dropout color processing apparatus comprising: an input section that inputs a document as multicolor image data; a color space conversion section that converts the image data into a specified color space; a histogram creation section that creates a histogram of data in the color space; an outline creation section that creates an outline of data distribution based on the histogram; a threshold generation section that creates a threshold value based on the created outline and creates an extraction region in a color space; a specified color conversion section that converts a pixel of the image data into specified color depending on whether or not a result of converting a pixel of the image data into the color space belongs to an extraction region in the color space; an output section that outputs a processed image; a first range specification section that specifies an “extracted-color-inclusive” image area for the image data; a second range specification section that specifies an “extracted-color-exclusive” image area for the image data; a histogram creation section that extracts color space distribution in the “extracted-color-inclusive” image area and part or all of the “extracted-color-exclusive” image area; a threshold generation section that generates a threshold value based on a result of the histogram extraction; wherein the means includes a first smoothing means, a second smoothing means, and a threshold generation section; wherein the first smoothing means generates an extracted-color-inclusive enveloping surface as distribution in a color space where an extracted-color-inclusive image region is extracted; wherein the second smoothing means generates an extracted-color-exclusive enveloping surface as distribution in a color space where an extracted-color-exclusive image region is extracted; and wherein the threshold generation section has a criterion of assuming an extracted color to be located at least inside an extracted-color-inclusive enveloping surface and outside an extracted-color-exclusive enveloping surface.