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Scaling Algorithm for Bit-Map Image

IP.com Disclosure Number: IPCOM000044572D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 50K

IBM

Related People

Kashiwagi, K: AUTHOR [+2]

Abstract

A scaling operation on a rectangular bit-map image basically consists of horizontal scaling and vertical scaling. The scaling algorithm in the prior art regards each pel (picture element) as a point having no width. The algorithm in this article considers the width of each dot so that we can get more natural scaling effect. The purpose of this article is to show a simple horizontal or vertical scaling algorithm which returns codes indicating how to do the next or succeeding operations. These operations are 1) INPUT, 2) OUTPUT, 3) OUT, CLEAR, then INPUT. This algorithm also is not concerned whether the scaling is an enlargement or reduction. Suppose that the horizontal or vertical size of the input image is m dots and that of the output image is n dots. Then the pel mapping of m dots to n dots is essential for scaling (Fig.

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Scaling Algorithm for Bit-Map Image

A scaling operation on a rectangular bit-map image basically consists of horizontal scaling and vertical scaling. The scaling algorithm in the prior art regards each pel (picture element) as a point having no width. The algorithm in this article considers the width of each dot so that we can get more natural scaling effect. The purpose of this article is to show a simple horizontal or vertical scaling algorithm which returns codes indicating how to do the next or succeeding operations. These operations are 1) INPUT, 2) OUTPUT, 3) OUT, CLEAR, then INPUT. This algorithm also is not concerned whether the scaling is an enlargement or reduction. Suppose that the horizontal or vertical size of the input image is m dots and that of the output image is n dots. Then the pel mapping of m dots to n dots is essential for scaling (Fig. 1). The basic idea of this algorithm is to approximate the diagonal line from (0.5, 0.5) by a sequence of unit-lines (length 1 or !2). Each end point of the unit-line indicates the mapping of input dot to output dot. Fig. 2 shows the approximation. Let Po be the current approximate point and P1, P2 and P3 be points adjacent to the point Po in the horizontal, vertical and oblique directions. The next approximate point is determined to be the point P3 with its distance to the diagonal line the shortest. Fig. 3 illustrates an example of a 7-dot to 3-dot reduction, and Fig. 4 illustrates an example of a 3-dot to...