Image processing method to remove halftone screens

Claim 1

An arrangement for reproducing an original image, comprising: scanner means which scans and digitizes the original image; controller means coupled to the scanner means to receive the digitized original image, perform a local structure analysis of the digitized original image, selectively apply a descreening filter to a region of the digitized original image based on the results of the local structure analysis to remove a specific frequency of the digitized image caused by halftone screens, allow a bypass of the descreening filter of other regions of the digitized image such that bypassed regions remain unfiltered by said descreening filter, and which produces a first signal representing filtered regions and unfiltered regions, said first signal corresponding of the digitized original image; a printer coupled to the controller to receive said first signal and which produces a gray level halftoned production of the original image; and wherein the descreening filter includes means for transforming the digitized image into a frequency domain, means for reducing the specific frequency content from the digitized image, and means for transforming the digitized image back into the spatial image domain and feedback means between the spatial domain and the frequency domain to iteratively reduce to a minimum the specific frequency in the digitized image.

Claim 3

A method of reproducing an original image, comprising: scanning an original image to produce a digitized image; performing a local structure analysis of the digitized image; selectively applying a descreening filter to a region of the digitized image based on the results of the local structure analysis to remove a specific frequency of the digitized image caused by halftone screens; bypassing the descreening filter with regions of the digitized image such that said bypassed regions remain unfiltered by said descreening filter; printing said filtered regions and said bypassed regions as a single, unified reproduction of the original image; and wherein the step of performing the local structure analysis includes the steps of; establishing a moving window for the digitized image around a central pixel; determining if the moving window is a low contrast window or a high contrast window; determining if there is a consistent transition in the moving window around the central pixel; and causing the application of the descreening filter to the moving window when the moving window is a high contrast window and there is not consistent transition in the moving window around the central pixel.

Claim 4

A method of reproducing an original image, comprising: scanning an original image to produce a digitized image; performing a local structure analysis of the digitized image; selectively applying a descreening filter to a region of the digitized image based on the results of the local structure analysis to remove a specific frequency of the digitized image caused by halftone screens; bypassing the descreening filter with regions of the digitized image such that said bypassed regions remain unfiltered by said descreening filter; printing said filtered regions and said bypassed regions as a single, unified reproduction of the original image; and wherein the step of performing the local structure analysis includes the steps of; establishing a moving window for the digitized image around a central pixel; determining if the moving window is a low contrast window or a high contrast window; determining if there is a consistent transition in the moving window around the central pixel; and causing the application of the descreening filter to the moving window when the moving window is a high contrast window and there is not consistent transition in the moving window around the central pixel.

Claim 10

A method of reproducing an original image, comprising: scanning an original image to produce a digitized image; performing a local structure analysis of the digitized image; selectively applying a descreening filter to a region of the digitized image based on the results of the local structure analysis to remove a specific frequency of the digitized image caused by halftone screens; bypassing the descreening filter with regions of the digitized image such that bypassed regions remain unfiltered by said descreening filter; printing filtered regions and bypassed regions as a single, unified reproduction of the original image; and wherein in the descreening filter the image is transformed to a frequency spectrum and a certain frequency is reduced and the modified image transformed into the spatial domain, and there is feedback between the spatial domain and the frequency domain to iteratively reduce to a minimum the certain screen frequency.

Claim 11

A method of reproducing an original image, comprising: scanning an original image to produce a digitized image; performing a local structure analysis of the digitized image; selectively applying a descreening filter to a region of the digitized image based on the results of the local structure analysis to remove a specific frequency of the digitized image caused by halftone screens; bypassing the descreening filter with regions of the digitized image such that bypassed regions remain unfiltered by said descreening filter; printing filtered regions and bypassed regions as a single, unified reproduction of the original image; and wherein in the descreening filter the image is transformed to a frequency spectrum and a certain frequency is reduced and the modified image transformed into the spatial domain, and there is feedback between the spatial domain and the frequency domain to iteratively reduce to a minimum the certain screen frequency.