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shear - Shear or rotate a raster image by an arbitrary angle

NAME

shear - Shear or rotate a raster image by an arbitrary angle

SYNOPSIS

CropShearImage(image,x_shear,y_shear,width,height,crop)

rotated_image=IntegralRotateImage(image,rotations)

RotateImage(image,degrees,crop,sharpen)

ShearImage(image,x_shear,y_shear,crop)

XShearImage(image,degrees,width,height,x_offset,y_offset,range_limit)

YShearImage(image,degrees,width,height,x_offset,y_offset,range_limit)

FUNCTION DESCRIPTIONS

CropShearImage

Function CropShearImage crops the sheared image as determined by the bounding box as defined by width and height and shearing angles.

The format of the CropShearImage routine is: 

        CropShearImage(image,x_shear,y_shear,width,height,crop)

A description of each parameter follows.

o image:
The address of a structure of type Image.

o x_shear, y_shear, width, height:
Defines a region of the image to crop.

o crop:
A value other than zero crops the corners of the rotated image and retains the original image size.

IntegralRotateImage

Function IntegralRotateImage rotates the image an integral of 90 degrees. It allocates the memory necessary for the new Image structure and returns a pointer to the rotated image.

The format of the IntegralRotateImage routine is: 

        rotated_image=IntegralRotateImage(image,rotations)

A description of each parameter follows.

o rotated_image:
Function IntegralRotateImage returns a pointer to the rotated image. A null image is returned if there is a a memory shortage.

o image:
The address of a structure of type Image.

o rotations:
Specifies the number of 90 degree rotations.

XShearImage

Procedure XShearImage shears the image in the X direction with a shear angle of 'degrees'. Positive angles shear counter-clockwise (right-hand rule), and negative angles shear clockwise. Angles are measured relative to a vertical Y-axis. X shears will widen an image creating 'empty' triangles on the left and right sides of the source image.

The format of the XShearImage routine is: 

        XShearImage(image,degrees,width,height,x_offset,y_offset,range_limit)

A description of each parameter follows.

o image:
The address of a structure of type Image.

o degrees:
A double representing the shearing angle along the X axis.

o width, height, x_offset, y_offset:
Defines a region of the image to shear.

YShearImage

Procedure YShearImage shears the image in the Y direction with a shear angle of 'degrees'. Positive angles shear counter-clockwise (right-hand rule), and negative angles shear clockwise. Angles are measured relative to a horizontal X-axis. Y shears will increase the height of an image creating 'empty' triangles on the top and bottom of the source image.

The format of the YShearImage routine is: 

        YShearImage(image,degrees,width,height,x_offset,y_offset,range_limit)

A description of each parameter follows.

o image:
The address of a structure of type Image.

o degrees:
A double representing the shearing angle along the Y axis.

o width, height, x_offset, y_offset:
Defines a region of the image to shear.

RotateImage

Function RotateImage creates a new image that is a rotated copy of an existing one. Positive angles rotate counter-clockwise (right-hand rule), while negative angles rotate clockwise. Rotated images are usually larger than the originals and have 'empty' triangular corners. X axis. Empty triangles left over from shearing the image are filled with the color defined by the pixel at location (0,0). RotateImage allocates the memory necessary for the new Image structure and returns a pointer to the new image.

Function RotateImage is based on the paper ``A Fast Algorithm for General Raster Rotatation'' by Alan W. Paeth. RotateImage is adapted from a similiar routine based on the Paeth paper written by Michael Halle of the Spatial Imaging Group, MIT Media Lab.

The format of the RotateImage routine is: 

        RotateImage(image,degrees,crop,sharpen)

A description of each parameter follows.

o status:
Function RotateImage returns a pointer to the image after rotating. A null image is returned if there is a memory shortage.

o image:
The address of a structure of type Image; returned from ReadImage.

o degrees:
Specifies the number of degrees to rotate the image.

o crop:
A value other than zero crops the corners of the rotated image and retains the original image size.

o sharpen:
A value other than zero sharpens the image after it is rotated.

ShearImage

Function ShearImage creates a new image that is a sheared copy of an existing one. Shearing slides one edge of an image along the X or Y axis, creating a parallelogram. An X direction shear slides an edge along the X axis, while a Y direction shear slides an edge along the Y axis. The amount of the shear is controlled by a shear angle. For X direction shears, x_shear is measured relative to the Y axis, and similarly, for Y direction shears y_shear is measured relative to the X axis. Empty triangles left over from shearing the image are filled with the color defined by the pixel at location (0,0). ShearImage allocates the memory necessary for the new Image structure and returns a pointer to the new image.

Function ShearImage is based on the paper ``A Fast Algorithm for General Raster Rotatation'' by Alan W. Paeth.

The format of the ShearImage routine is: 

        ShearImage(image,x_shear,y_shear,crop)

A description of each parameter follows.

o status:
Function ShearImage returns a pointer to the image after rotating. A null image is returned if there is a memory shortage.

o image:
The address of a structure of type Image; returned from ReadImage.

o x_shear, y_shear:
Specifies the number of degrees to shear the image.

o crop:
A value other than zero crops the corners of the rotated image and retains the original image size.

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