Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-06-01
2001-11-27
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S522000, C358S530000, C358S463000, C358S464000, C382S171000, C382S228000, C382S275000
Reexamination Certificate
active
06323957
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to document reproduction and more particularly to the removal of undesirable and unintended dots of toner or ink produced in a background area of a document. As will be detailed below, the primary use of the present invention is in connection with marking engines used in digital black/white and color copiers and printers. However, it is to be appreciated that the present invention can have uses in other fields where noise removed is beneficial.
FIG. 1
illustrates the image path of a color digital copier A, including scanner
10
, image processing electronics
12
and printer
14
. An original document is scanned by scanner
10
, and converted into a stream of pixels. Image processing electronics
12
manipulates the pixel stream into a format suitable for use by printer
14
, which selectively transfers toner or ink to a blank piece of copy paper, commonly a white piece of paper, thereby reproducing the images of the original document onto the copy paper.
Each scanned pixel is represented by three 8-bit values 20 that measure the intensity of the three primary colors (i.e. red, green and blue), such a representation being in what is known in the art as a 24-bit RGB color space. Black is represented by all three values of RGB being equal to 0, white is represented by all three values being equal to the maximum 8-bit value 255, and gray is represented by all three values being an equal value. In existing color digital copiers, the printer functions in a non-RGB color space which more closely mimics the human eye. Examples of such color spaces include CMYK, YCC, and LAB color spaces, the concepts of which are well known in the art. The whitest pixel produced by a CMYK printer consists of no toner or ink located at that pixel position. Therefore, the whitest pixel is limited by the whiteness of the copy paper.
FIG. 2
graphically represents the RGB color space where each pixel is represented by three 8-bit values (0-255). If a user wishes to increase or decrease the luminance of an output document, it is necessary to adjust each of the colors of the RGB color space by an equal amount such that the color of the pixels do not change, but rather only the luminance is altered.
On the other hand as can be seen in
FIG. 3
, which is a graphical representation of a color space such as YCC (where C
0
=the intensity value and C
1
and C
2
represent the hue of a color), intensity can be altered by changing the value of C
0
without requiring a corresponding change to the C
1
or C
2
values. With attention to the C
1
and C
2
values of
FIG. 3
, the further away from the origin, the more saturated the color value (i.e. the deeper the hue). Also, if the C
0
value is set to 0, then the values of. C
1
, C
2
are irrelevant since the color will be black. Similarly, if the C
0
value is made equal to its maximum, i.e. 255, then it does not matter what the values of C
1
, C
2
are since the color will be pure-white.
Thus, by moving from the RGB color space to a color space more closely mimicking the human eye, such as the YCC or LAB color spaces, it is easier to control the luminance and hues of the documents being reproduced.
In order for scanners which scan images into the RGB color space and printers which operate in color spaces, such as CMYK, to function together in the same copier, a color space conversion takes place through the use of color space converter
16
, whereby over 16 million colors in the RGB color space (2
24
) are converted to the 16 million colors of the YCC or LAB color space (2
24
). Thereafter, the pixels are provided to render
18
which converts the 16 million colors in the YCC color space to the 16 colors of the CMYK color space (2
4
) and then passes the pixels to printer
14
.
FIG. 1
also shows microcontroller
19
, which provides intelligence to control operation of color digital copier A.
Another consideration regarding digital color copiers is that existing color marking engines (e.g. laser and ink jet) cannot satisfactorily reproduce extremely unsaturated colors (known as near-white). The resulting reproduction consists of a few widely scattered small dots of color (i.e. background noise), in the background of the copy paper. The term background refers to the region of the source document that has no image imposed on it so that the underlying paper is viewed. Common background types are white copy paper, colored copy paper, newspaper, magazine paper and photographs.
When the background of the source document is scanned, even if the paper appears white to a person, it appears off-white i.e. near-white, to a scanner. This off-white color is an extremely unsaturated color, hence the perceptually white background of the original is reproduced with colored dots scattered around the page. Viewed at a far distance, the region looks like the near-white original color but at a typical viewing distance the dots are quite noticeable and objectionable.
These near-white pixels are created by the combination of scanner inaccuracies, source document paper inconsistencies, and actual near-white pixels in the source document.
To overcome the above, the present invention provides a system that removes the undesirable background noise, in the form of unwanted dots of color, located in a background area of a document.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, provided is a system which eliminates background noise from a document to be reproduced. The system includes a device for acquiring statistics for at least some pixels of a pixel stream generated by a document scanner. Statistics and characteristics of the document are extracted from the pixels to determine a background color of the document to be reproduced. The value of the determined background color is then compared with incoming pixels of the scanned document to determine color dispersion in the background. Pixels found to be “near” background color values are manipulated to become pure-white by changing the luminance to maximum, pixels found to be “far” from the background color values are left unchanged, and pixels between “near” and “far” are altered in a linear manner. The manipulated pixels are then forwarded to a printer whereby a document is printed which has eliminated undesirable background dots, i.e. noise, within a document.
The present invention may be used in a digital color copier as well as black and white copiers wherein the system includes a statistics gathering (STS) module which acquires statistics on the pixels scanned by a scanner. The pixels are then provided to a controller MIC module which manipulates the statistics to determine background color values. These background color values along with additional statistics define areas where a pixel will be changed to white, where a pixel will not be changed, and where a pixel will be changed linearly.
In a more limited aspect of the present invention, a reference background value and a value of an incoming pixel are compared to determine the color distance the incoming pixel is located from the background reference value.
The RTE module accepts a pixel stream from the scanner and performs a transform. This transform is used to remove background noise. The RTE determines the three dimensional color distance squared between each incoming pixel and a reference pixel (supplied by the MIC module). The RTE module applies a linear stretch to a C
0
value of each pixel. Pixels with a color “near” to the reference pixel are stretched so that the C
0
component becomes pure-white. Pixels with a color “far” from the reference pixel are not changed. In a transition region between the “near” and “far”, pixels are stretched in a linear fashion.
In accordance with a more limited aspect of the present invention, the regions of transition are defined by an inner three dimensional ellipse and an outer three dimensional ellipse formed around a center reference point.
In accordance with another feature of the invention, a color digital copier implements the present i
Fay Sharpe Fagan Minnich & McKee LLP
Rogers Scott
Xerox Corporation
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