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// Geometric Tools, LLC
// Copyright (c) 1998-2014
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt
// http://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
//
// File Version: 5.0.0 (2010/01/01)
#include "ExtractRidges.h"
WM5_CONSOLE_APPLICATION(ExtractRidges);
//----------------------------------------------------------------------------
ExtractRidges::ExtractRidges ()
:
ConsoleApplication("SampleImagics/ExtractRidges")
{
}
//----------------------------------------------------------------------------
int ExtractRidges::Main (int, char**)
{
std::string imageName = Environment::GetPathR("Head.im");
ImageDouble2D image(imageName.c_str());
// Normalize the image values to be in [0,1].
int quantity = image.GetQuantity();
double minValue = image[0], maxValue = minValue;
int i;
for (i = 1; i < quantity; ++i)
{
if (image[i] < minValue)
{
minValue = image[i];
}
else if (image[i] > maxValue)
{
maxValue = image[i];
}
}
double invRange = 1.0/(maxValue - minValue);
for (i = 0; i < quantity; ++i)
{
image[i] = (image[i] - minValue)*invRange;
}
// Use first-order centered finite differences to estimate the image
// derivatives. The gradient is DF = (df/dx, df/dy) and the Hessian
// is D^2F = {{d^2f/dx^2, d^2f/dxdy}, {d^2f/dydx, d^2f/dy^2}}.
int xBound = image.GetBound(0);
int yBound = image.GetBound(1);
int xBoundM1 = xBound - 1;
int yBoundM1 = yBound - 1;
ImageDouble2D dx(xBound, yBound);
ImageDouble2D dy(xBound, yBound);
ImageDouble2D dxx(xBound, yBound);
ImageDouble2D dxy(xBound, yBound);
ImageDouble2D dyy(xBound, yBound);
int x, y;
for (y = 1; y < yBoundM1; ++y)
{
for (x = 1; x < xBoundM1; ++x)
{
dx(x, y) = 0.5*(image(x+1, y) - image(x-1, y));
dy(x, y) = 0.5*(image(x, y+1) - image(x, y-1));
dxx(x, y) = image(x+1, y) - 2.0*image(x, y) + image(x-1, y);
dxy(x, y) = 0.25*(image(x+1, y+1) + image(x-1, y-1)
- image(x+1, y-1) - image(x-1, y+1));
dyy(x, y) = image(x, y+1) - 2.0*image(x, y) + image(x, y+1);
}
}
dx.Save("dx.im");
dy.Save("dy.im");
dxx.Save("dxx.im");
dxy.Save("dxy.im");
dyy.Save("dyy.im");
// The eigensolver produces eigenvalues a and b and corresponding
// eigenvectors U and V: D^2F*U = a*U, D^2F*V = b*V. Define
// P = Dot(U,DF) and Q = Dot(V,DF). The classification is as follows.
// ridge: P = 0 with a < 0
// valley: Q = 0 with b > 0
ImageDouble2D aImage(xBound, yBound);
ImageDouble2D bImage(xBound, yBound);
ImageDouble2D pImage(xBound, yBound);
ImageDouble2D qImage(xBound, yBound);
for (y = 1; y < yBoundM1; ++y)
{
for (x = 1; x < xBoundM1; ++x)
{
Vector2d gradient(dx(x, y), dy(x, y));
Matrix2d hessian(dxx(x, y), dxy(x, y), dxy(x, y), dyy(x, y));
EigenDecompositiond decomposer(hessian);
decomposer.Solve(true);
aImage(x,y) = decomposer.GetEigenvalue(0);
bImage(x,y) = decomposer.GetEigenvalue(1);
Vector2d u = decomposer.GetEigenvector2(0);
Vector2d v = decomposer.GetEigenvector2(1);
pImage(x,y) = u.Dot(gradient);
qImage(x,y) = v.Dot(gradient);
}
}
aImage.Save("a.im");
bImage.Save("b.im");
pImage.Save("p.im");
qImage.Save("q.im");
// Use a cheap classification of the pixels by testing for sign changes
// between neighboring pixels.
ImageRGB82D result(xBound, yBound);
for (y = 1; y < yBoundM1; ++y)
{
for (x = 1; x < xBoundM1; ++x)
{
unsigned char gray = (unsigned char)(255.0f*image(x, y));
double pValue = pImage(x, y);
bool isRidge = false;
if (pValue*pImage(x-1 ,y) < 0.0
|| pValue*pImage(x+1, y) < 0.0
|| pValue*pImage(x, y-1) < 0.0
|| pValue*pImage(x, y+1) < 0.0)
{
if (aImage(x, y) < 0.0)
{
isRidge = true;
}
}
double qValue = qImage(x,y);
bool isValley = false;
if (qValue*qImage(x-1, y) < 0.0
|| qValue*qImage(x+1, y) < 0.0
|| qValue*qImage(x, y-1) < 0.0
|| qValue*qImage(x, y+1) < 0.0)
{
if (bImage(x,y) > 0.0)
{
isValley = true;
}
}
if (isRidge)
{
if (isValley)
{
result(x, y) = GetColor24(gray, 0, gray);
}
else
{
result(x, y) = GetColor24(gray, 0, 0);
}
}
else if (isValley)
{
result(x, y) = GetColor24(0, 0, gray);
}
else
{
result(x, y) = GetColor24(gray, gray, gray);
}
}
}
result.Save("result.im");
return 0;
}
//----------------------------------------------------------------------------
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