|| ||      

---

An example of a generalized convolution: Uniform filter

Uniform filtering is implemented by HxUniform. However, for this example we will use HxUniformNonSep since its code is a little simpler. HxUniformNonSep is a non separated version of HxUniform.

/*
 *  Copyright (c) 2001, University of Amsterdam, The Netherlands.
 *  All rights reserved.
 *
 *  Author(s):
 *  Dennis Koelma           (koelma@science.uva.nl)
 */

#include "HxUniformNonSep.h"
#include "HxMakeFromValue.h"

HxImageRep
HxUniformNonSep(HxImageRep im, HxSizes sizes)
{
    // An image signature for a 2D image with 64-bit real valued scalar pixels
    HxImageSignature sig(im.dimensionality(), 1, REAL_VALUE, 64);

    // The pixel value of the uniform kernel
    double val = 1.0 / (sizes.x() * sizes.y() * sizes.z());

    // Now construct the kernel image
    HxImageRep kernel = HxMakeFromValue(sig, sizes, val);

    // and apply the operation
    return im.generalizedConvolution(kernel, "mul", "addAssign");
}

Basically, a uniform filter is a convolution with a uniform kernel. A convolution is performed by supplying the generalized convolution with multiplication and addition as basic operations.

A uniform kernel image is constructed from the following parameters:

• An HxImageSignature to specify the type of image to be created,
• HxSizes to specify the extend of the image, and
• an HxValue to give the pixels in the image a value.

MidApp

Read 'flamingo' from disk. Apply the function HxUniformNonSep (menu 'GlobalOps/Images/Filter') with parameter '5 5'.

In order to do uniform filtering via a generic function we first have to construct the kernel image and then perform a convolution on the image via the generalized convolution.

• Select 'HxMakeFromValue' from the 'GlobalOps/Images/Generation' menu. Enter 'unif5x5' for the result name. Select 'SIG2DDOUBLE' for the signature. Enter '5 5' for the sizes and '0.04' for the value.
• Select 'generalizedConvolution' from the 'ImageRep' menu. Select 'flamingo' for the ImageRep object and 'unif5x5' for the kernel. Enter 'mul' for gMul and 'addAssign' for gAdd. Select 'SOURCE_PREC' for the precision and '_nil' for the taglist.

IDL script

Uniform filtering is demonstrated in demoUniform.cs

# Demo: shows how to apply a uniform 5x5 filter to Horus images

println("Enter name of image, e.g. c:/images/flamingo.tif");
name = getline();

# Read image from disk
a = OPS.HxMakeFromFile(name);

# An image signature for a 2D image with 64-bit real valued scalar pixels
sig = HxCorba.ImageSignature.SIG2DDOUBLE;

# Define the sizes of the neighbourhood
sizes = HxCorba.Sizes(5, 5, 1);

# The pixel value of the uniform kernel
val = HxCorba.PixValue(HxCorba.PixValueTag.SD, 1.0 / (sizes.x * sizes.y * sizes.z));

# Now construct the kernel image
kernel = OPS.HxMakeFromValue(sig, sizes, val);

# Apply the operation
empty = CTOR.emptyTagList();
prec = HxCorba.ResultPrecision.ARITH_PREC;
b = a.generalizedConvolution(kernel, "mul", "addAssign", prec, empty);

and executed with exec("x:/HxSamples/Scripts/demoUniform.cs");.

Matlab

Uniform filtering is demonstrated in demoUniform.m

%demoUniform  Demo: shows how to apply a uniform 5x5 filter to Horus images

echo on
clc

name = input('Enter name of image, e.g. c:/images/flamingo.tif\n', 's');

% Read image from disk
a = OPS.HxMakeFromFile(name);

% Display the image
hxShow(a);

pause % Press any key to continue

% An image signature for a 2D image with 64-bit real valued scalar pixels
sig = HxCorba.ImageSignature.SIG2DDOUBLE;

% Define the sizes of the neighbourhood
sizes = HxCorba.Sizes(5, 5, 1);

% The pixel value of the uniform kernel
val = HxCorba.PixValue;
val.scalarDouble(1.0 / (sizes.x * sizes.y * sizes.z));

% Now construct the kernel image
kernel = OPS.HxMakeFromValue(sig, sizes, val);

% Apply the operation
empty = CTOR.emptyTagList;
% Due to a bug in Matlab, the following statement crashes in a script.
%prec = HxCorba.ResultPrecision.ARITH_PREC;
prec = HxCorba.ResultPrecision.from_int(1);
b = a.generalizedConvolution(kernel, 'mul', 'addAssign', prec, empty);

% And display it
hxShow(b);

and executed with demoUniform.

---

Go to the next section or return to the index.

---