Image analysis – Histogram processing – For setting a threshold
Patent
1986-11-19
1988-07-19
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
340727, 358 22, 364731, G06K 932
Patent
active
047590769
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
This invention relates to an image rotating system by an arbitrary angle for use in image processing techniques.
BACKGROUND OF ART
Heretofore, a system resorting to affine transformation has been usual in an attempt to rotate two-dimensional image data. Rotating an image through affine transformation requires arithmetic operations based on the following equation (1); ##EQU1## where X, Y are coordinates of the original pixel, x, y are coordinates after transformation and .theta. is an rotated angle of image data. When handling image data such as a displayed image, the above transformation requires to implementation of arithmetic operations of the equation (1) pixel-by-pixel. Thus, a large amount of computation is needed, particularly when rotating a large image and, therefore, it was considered very difficult to obtain a rotated image at high speeds.
Accordingly, as disclosed in Japanese Patent LaidOpen No. 55-94145(1980) by way of example, there has been proposed a system wherein an image is skewed to obtain a rotated image in a pseudo manner, i.e., that an image is first subjected to skew transformation by an angle .theta. in a horizontal direction and then another skew transformation by an angle .theta. in a vertical direction. Such a system resorting to skew transformation by an angle .theta. will be described with reference to FIG. 4. Referring to the figure, 400 is an original image, 401 is the image after skew transformation in a horizontal direction, and 402 is an image derived from 401, which was derived from the original image after the skew transformation in a horizontal direction, after another skew transformation in a vertical direction. These skew transformations can be achieved at high speeds by a suitable method such as skew scan. The skew transformation method can be described by the following equation (2): ##EQU2## where .theta.; minute angle
Because the conventional image rotating system by an arbitrary angle was implemented as mentioned above, approximation of the equation (2) will lose its effectiveness and the rotated image will be distorted, as a rotation angle .theta. increases. As a result, the conventional system can be applied only while the rotation angle is within a range of certain minute angles.
SUMMARY OF THE INVENTION
One object of this invention is to provide an image rotating system by an arbitrary angle to produce a precise rotated image at high speeds without resorting to approximation of the arithmetic equation, the system being featured in that a skew transformation is implemented for respective skew angles in horizontal and vertical directions corresponding to a desired rotation angle three times alternately, so that affine transformation of an image requiring large amount of computation may be replaced by triple skew transformations, thereby rotating any twodimensional image data by a desired angle.
In accordance with the invention, since skew transformation is implemented for respective skew angles in X- and Y-directions corresponding to a desired rotation angle three times alternately, image rotation can be performed without needing arithmetic operations of affine transformation, at high speeds. The invention can also offer an effect that two-dimensional image data rotated by an arbitrary angle is obtainable more precisely than the conventional system which resorts to double skew transformations.
BRIEF DESCRIPTION OF DRAWING
FIG. 1 is a diagram showing the procedure of skew transformations according to one embodiment of the invention;
FIG. 2 is an illustration showing a two-dimensional image according to one embodiment of skew transformation in an X-direction;
FIG. 3 is a diagram showing the process of image rotation according to one embodiment of the invention; and
FIG. 4 is a diagram for explaining a conventional image rotating system by an arbitrary angle.
BEST MODE OF THE PRESENT INVENTION
Hereinafter, one embodiment of the invention will be described with reference to the drawings. It is to be noted that the description will be made f
REFERENCES:
patent: 4527155 (1985-07-01), Yamaki et al.
patent: 4618991 (1986-10-01), Tabata et al.
patent: 4622588 (1986-11-01), Chapuis et al.
Casey et al., IBM Technical Disclosure Bulletin, vol. 13, No. 11, Apr. 1971, pp. 3267-3268.
"High Speed Image Scaling for Integrated Document Management", Tabata et al., Office Information System Conference, Jun. 1984, Toronto, Canada edited by Clarence A. Ellis, vol. 5, Nos. 1-2.
Kameyama Masatoshi
Tanaka Atsushi
Boudreau Leo H.
Mitsubishi Denki & Kabushiki Kaisha
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