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AREA MAPPING APPROACH FOR RESOLUTION CONVERSION

IP.com Disclosure Number: IPCOM000026906D
Original Publication Date: 1994-Apr-30
Included in the Prior Art Database: 2004-Apr-07
Document File: 6 page(s) / 271K

Publishing Venue

Xerox Disclosure Journal

Abstract

Proposed is an area mapping procedure for resolution and gray level conversion in which the sizes of input and output pixels are allowed to differ. The approach can simulate gray levels from a black and white input and it can provide a very wide range of conversion ratios. The approach of the resolution conversion is based on a very simple idea of mapping the optical density, which is represented by the pixels of the raw bit map, for a given input area, to the corresponding output area. The size of the output area is identical to the input area. But, the sizes of the input and output pixels are different. The key point in this approach is to maintain the optical density and image structure of the output as close to the input as possible. To achieve this goal, the following procedure is used:

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XEROX DISCLOSURE JOURNAL

AREA MAPPING APPROACH FOR RESOLUTION CONVERSION US. C1.358/282 Henry R. Kang
Robert E. Coward

Proposed Classification

Int. C1. H04n 01/40

7- /400 1 t L 1

XEROX DISCLOSURE JOURNAL - Vol. 19, No. 2 MarcldApril 1994 173

[This page contains 1 picture or other non-text object]

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AREA MAPPING APPROACH FOR RESOLUTION CONVERSION

(Cont'd)

INPUT PIXEL CORNER MIDDLE CENTER

Table - Weighing Factors of 300x300~2 to

400x400~4 Resolution Conversion

OUTPUT PIXEL

CORNER MIDDLE CENTER 27 9 3

0 18 6 0 0 12

174 XEROX DISCLOSURE JOURNAL - Vol. 19, No. 2 MarcWApril 1994

[This page contains 1 picture or other non-text object]

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AREA MAPPING APPROACH FOR RESOLUTION CONVERSION

(Cont'd)

Proposed is an area mapping procedure for resolution and gray level conversion in which the sizes of input and output pixels are allowed to differ. The approach can simulate gray levels from a black and white input and it can provide a very wide range of conversion ratios. The approach of the resolution conversion is based on a very simple idea of mapping the optical density, which is represented by the pixels of the raw bit map, for a given input area, to the corresponding output area. The size of the output area is identical to the input area. But, the sizes of the input and output pixels are different. The key point in this approach is to maintain the optical density and image structure of the output as close to the input as possible. To achieve this goal, the following procedure is used:

          Determine the window sizes of input and output images. The window sizes depend upon the image resolutions. They are determined by using the greatest common denominator (GCD).

1.

(Ws)i = (R)i/(GCD)i

where i = the x or y coordinate; Ws = window size; and R = the image resolution.

As an example, the GCD in the 300 x 300 to 400 x 400 x 4 spots per inch conversion is 100, such that the input window is 3 x 3 and the output widow 4 x 4 as shown in the Figure.

      2. Assign a gray value to the output pixels for a given input window. Output pixels fall into three types 300 x 300 to 400 x 400 conversions:

a) b)


c)

corner pixels shown as the black areas in the figure, middle pixels shown as the shaded areas in the figure, and center pixels shown as the white areas in the figure.

Depending on the area coverage, assign a weight to each input pixel within the boundary of a given output pixel. The output pixel value (gray or binary) is then calculated using the following equation.

Po = (Wi*Pi + P)/Ua

where Po = the output pixel value,

Wi = the weighing factors, Pi = the input pixel values, Ua = the area of an output pixel, P = the round-off value (T = Ua/2), and n = the number of input pixels within the boundary of an input

pixel.

XEROX DISCLOSURE JOURNAL - Vol. 19, No. 2 MarcWApril 1994 175

[This page contains 1 picture or other non-text object]

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AREA MAPPING APPROACH FOR RESOLUTION CONVERSION

(Cont'd)

To take advantage of the integral arithmetic, a...