Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-07-22
2001-03-13
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000, C382S254000, C382S264000, C382S205000
Reexamination Certificate
active
06201613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to the field of image processing. In particular, the invention relates to automatic image enhancement of halftone and continuous tone images.
2. Description of Related Art
Automatic image enhancement (AIE) is a technology that operates on sampled images and invokes image processing operations on the sampled images based on analysis of the images. Automatic image enhancement automatically corrects image deficiencies through adjustments of exposure, contrast, sharpness, color balance and saturation. After analysis of the image is performed to determine what action, if any, to perform on the image, the appropriate image processing is applied to the image. In the past, automatic image enhancement was done almost exclusively on continuous tone (contone) images, such as photographs.
SUMMARY OF THE INVENTION
In the office environment, it is much more likely to encounter a halftone original than a contone original. Halftone originals are often degraded when scanned or reproduced, for example, by photocopying.
This invention provides a system and method for automatically enhancing degraded halftone images as effectively as degraded contone images can be enhanced.
This invention provides a system and method that automatically enhances halftone images using a spatial filter.
This invention provides a low-pass spatial filter as the spatial filter.
This invention provides a pyramid filter as a two-dimensional embodiment of the spatial filter.
This invention provides a triangular filter as a one-dimensional embodiment of the spatial filter.
Due to the human eye's inability to individually resolve the pixels of a halftone image at normal viewing distance, a halftone image appears to have tone gradations like a contone image. However, pixel-by-pixel analysis, or statistics collection, of the halftone image may produce a different result than the same pixel-by-pixel analysis of a similarly-degraded contone image. This difference usually produces disappointing results when automatic image enhancement is applied to a degraded halftone image.
To avoid the disappointing results of applying automatic image enhancement to a degraded halftone image, the system and method of this invention smooth the scanned halftone image using a low-pass spatial filter prior to collecting statistics, to obtain more accurate information about the scanned halftone image. Although many low-pass spatial filter configurations will improve conventional automatic image enhancement methods, a 7×7 two-dimensional pyramid low-pass filter is an example of a low-pass spatial filter which provides satisfactory results. A 15×1 one-dimensional triangular lowpass filter can also be used in the invention. Compared to two-dimensional filtering, one-dimensional filtering is less expensive since it does not need scan line buffers to store multiple scan line image data. Using a 15×1 one-dimensional filter in the invention provides acceptable results so that it is preferable in a cost sensitive application.
By applying the low-pass spatial filter to the scanned halftone image, the image density of each pixel is adjusted to eliminate large image density differences between adjacent pixels. As a result, the halftone variation is “smoothed out”, which provides a better starting point for the statistics collection.
The apparatus and method of the invention can also be applied to continuous tone images and it is not necessary to designate whether the original image is a halftone image, a continuous tone image or a combination of halftone and continuous tone images.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.
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Banton Martin Edward
Shiau Jeng-Nan
Zhang Yeqing
Oliff & Berridg,e PLC
Rogers Scott
Xerox Corporation
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