C:/Users/Malcolm/Documents/temp/binaryimagelibrary/rotatebyshear.c File Reference

#include <stdlib.h>
#include <math.h>
#include <assert.h>

Macros
#define	PI   3.1415926535897932384626433832795

Functions
int	rotatebyshear (unsigned char *binary, int width, int height, double cx, double cy, double theta, unsigned char *out)

Detailed Description

Rotate by shear.

By Malcolm McLean

Rotate an image using the shearing method, which avoids sampling artifacts as preserves pixel values.

Part of the binary image processing library.

Function Documentation

int rotatebyshear	(	unsigned char *	binary,
		int	width,
		int	height,
		double	cx,
		double	cy,
		double	theta,
		unsigned char *	out
	)

Rotate an image, using the shearing method.

Parameters

[in]	binary	- the binary or colour-indexed image
	width	- image width
	height	- image height
	cx	- centre x, y co-ordinates (pass in 1.5, 1.5 for the centre of a 3x3 image)
	cy	- centre x, y co-ordinates (pass in 1.5, 1.5 for the centre of a 3x3 image)
	theta	- angle to rotate by
	out[out]	- buffer for output (can't be the same as input)

Returns

: 0 for success

Note

conventional image rotation by the matrix method causes destination pixels to be sub-samples of source pixels. This isn't a problem with continous tone images where the new pixel values can be obtained by interpolation. However with binary or colour-index images, interpolation isn't possible. The shearing method preserves the pixels, at some cost in rotational accuracy.

Margaret Thatcher (1925-2013) greyscale photograph

Mrs Thatcher rotated

Test card (256 colour-indexed)

Test card rotated