IMAGE commands


PROGRAM NAME

igradient - Gradient Operators (Roberts, Sobel, Prewitt, Isotropic)

DESCRIPTION

igradient takes an image and performs the differentiation (high pass spatial filtering or edge enhancement) operation by using standard gradient operators. The standard gradient operators supported by the igradient routine are: Robert's, Sobel, Prewitt and Isotropic. The Robert's operators use a 2x2 kernel, whereas the other three use a 3x3 kernel. Each operator uses two templates to enhance edges in the horizontal and vertical directions only. For edge enhancements in other directions other operators should be used.

There are two approximations to the true gradient. The user can select between calculating the magnitude of the gradient by using squares and square roots (Euclidean distance evaluation), or by using absolute differences. The latter is computationally faster.

Mask data is ignored.

REQUIRED ARGUMENTS

-i
type: infile
desc: input image filename
-o
type: outfile
desc: output image filename

Mutually Exclusive Group; you must specify ONE of:

-roberts
type: flag
desc: Perform Roberts gradient operation
OR
-sobel
type: flag
desc: Perform Sobel gradient operation
OR
-prewitt
type: flag
desc: Perform Prewitt gradient operation
OR
-isotropic
type: flag
desc: Perform Isotropic gradient operation

OPTIONAL ARGUMENTS

-abs
type: boolean
desc: Calculate gradient using absolute value or square root
default: false

EXAMPLES

% igradient -i source_image.viff -o dest_image.viff 

performs edge enhancement using the default values, i.e., uses the Sobel templates and uses absolute differences to approximate the gradient.

% igradient -i source_image.viff -o dest_image.viff -isotropic -abs 1
performs edge enhancement using the Isotropic templates and determines the gradient by evaluating Euclidean distances.

SEE ALSO

klinearop(1)

RESTRICTIONS

COMPLEX data processing is not supported.

REFERENCES

COPYRIGHT

Copyright (C) 1993 - 1997, Khoral Research, Inc. ("KRI") All rights reserved.