Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-04-20
2001-01-16
Rogers, Scott (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000, C382S169000, C382S171000
Reexamination Certificate
active
06175427
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention is directed towards a system and method for correcting tonal reproduction curves (TRCs) for independent regions of a compound document. More particularly, the present invention is directed to a system and method which generates the correct TRCs using only a single scan of the compound document.
BACKGROUND OF THE PRESENT INVENTION
In the past, a typical application for copiers or scan-to-print image processing systems was to reproduce an input image as accurately as possible, i.e., render a copy. Thus, copies have been rendered as accurately as possible, flaws and all. However, as customers become more knowledgeable in their document reproduction requirements, they recognize that an exact copy is often not what they want. Instead, they would rather obtain the best possible document output. Until recently, image quality from the output of a copier or a scan-to-print system was directly related to the input document quality.
Image enhancement, as used herein, refers only to processes which improve the output quality of the image, and not to internal operations, necessitated by particular processor limitations. Thus, for example, changing TRC for better reproduction of an image is an enhancement operation. However, reducing the number of colors representing image to place an image into a particular file format, such as GIF files, or .BMP files, is not an enhancement operation.
Photography has long dealt with this issue. Analog filters and illumination variations can improve the appearance of pictures in the analog photographic process. Thus, for example, yellow filters enhance the appearance of white clouds against a blue sky in black and white images. Further, various electrophotographic devices, including digital copiers, can clean up and improve images by adjustment of threshold, filtering, or background suppression. Generally, these methods are manual methods which a user must select on an image by image basis. Unfortunately, the casual user is not skilled enough to perform these operations. The inability to perform image enhancement operations is exacerbated when additionally dealing with color controls.
Three possible choices are presented by the art in the area of image enhancement. In the first case, we can do nothing. Such a system is a stable system, in that it does no harm to an image. This is a common approach taken to reproduction. However, the output documents of such a system are sometimes not satisfactory to the ultimate customer.
In a second case of image enhancement, the image can always be processed. It turns out that an improvement can usually be made to an image if certain assumptions are made that are accurate for most cases. In an exceptionally large set of images, increasing contrast, sharpness, and/or color saturation, will improve the image. This model tends to produce better images, but the process is unstable, in that for multi-generation copying, increases in contrast, saturation, or sharpness are undesirable and ultimately lead to a severe image degradation. Further, the process may undesirably operate on those images which are good ones.
Accordingly, we arrive at our third case of image enhancement, a process of automated image enhancement which operates to vary images which are not perceived as good images, but does not operate on images which do not need to be improved.
Many improvements can be made to an image, including luminance enhancement (e.g. U.S. Pat. No 5,450,502); sharpness enhancement (e.g., U.S. Pat. No. 5,363,209); exposure adjustment (e.g. U.S. Pat. No. 5,414,538); color balance correction (e.g., U.S. Pat. No. 5,357,352, U.S. Pat. No. 5,371,615) or contrast enhancement (U.S. Pat. No. 5,581,370); color saturation correction (e.g. U.S. Pat. No. 5,450,217), etc. These processes can be used together in a predictive mode that does not require iterative processing (e.g. U.S. Pat. No. 5,347,374). Generally, these processing methods operate by modifying a set of tonal reproduction curves (TRCs). The output image is achieved by using TRCs, operating either on the luminance channel of an image expressed LC
1
C
2
coordinates, or preferably on each channel in a color density space description of the image in Red-Green-Blue (RGB) coordinates. The entire contents of U.S. Pat. Nos. 5,450,502; 5,363,209; 5,414,538; 5,357,352; 5,371,615; 5,581,370; 5,450,217; and 5,347,374 are hereby incorporated by reference.
Moreover, automatic image enhancement must be selective in its application. For example, when processing a compound document, a document with independent regions such as graphics, text, halftones, photographs, etc., the image enhancement for one region may not necessarily be applicable to another region. Thus, the image enhancement routine must selectively apply one or more of the above noted correction processes to each independent region.
Conventionally, to determine the tonal correction for independent regions on compound documents, two separate scans of the document was required. More specifically, as illustrated in
FIG. 2
, the image would be initially scanned at step S
1
and from the image data generated from this scan the desired image regions or windowing would be identified at step S
2
. Thus, upon the completion at step S
2
, the various windows or regions of the image being scanned will have been identified. Thereafter, at step S
3
, the image is scanned again and the image data generated therefrom is utilized in step S
4
to generate histogram data for each identified region. In other words, conventionally, it took two scans of the image to generate the image regions and the histograms for each identified region.
After these two sets of data is generated, step S
5
uses the information generated at step S
2
and S
4
to enhance the image data; i.e., create the tonal correction curve for the image data for that region so that the image data can be outputted at step S
6
. Thus,
FIG. 2
illustrates a conventional automatic image enhancement routine for correcting tonal reproduction curves for independent regions on a compound image. Although the method described with respect to
FIG. 2
produces a high quality image, this method and process negatively impacts the productivity of the reprographic system More specifically, by requiring two separate scans of the image to generate the window data and the histogram data, respectively, the automatic image enhancement routine impacts productivity by one-half. Therefore, it is desirable to achieve the automatic image enhancement improvement while eliminating any adverse impact upon productivity.
SUMMARY OF THE PRESENT INVENTION
One aspect of the present invention is a method for providing necessary image information to enable tonal correction for independent regions of a compound document. The method scans an image and generates image data; generates histogram data from the image data for a predetermined number of regions corresponding to the image; generates, during the generation of the histogram data, a window corresponding to an independent area of the image that requires image enhancement; and associates corresponding histogram data with the generated window.
A second aspect of the present invention is a system for providing necessary image information to enable tonal correction for independent regions of a compound document. The system includes a scanner to scan an image and generate image data; a histogram circuit, operatively connected to the scanner, to generate histogram data from the image data for a predetermined number of regions corresponding to the image; a windowing circuit, operatively connected to the scanner and in parallel with the histogram circuit, to generate a window corresponding to an independent area of the image that requires image enhancement; and an association circuit to associate corresponding histogram data with the generated window.
Further objects and advantages of the present invention will become apparent from the following descriptions of the various embodiments and characteristic features of the pre
Lehmbeck Donald R.
Shiau Jeng-Nan
Williams Leon C.
Nickerson Michael J.
Rogers Scott
Xerox Corporation
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