Hough transform: Difference between revisions

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=={{header|Java}}==

'''Code:'''

<lang Java>import java.awt.image.*;

import java.io.File;

import java.io.IOException;

import javax.imageio.*;

public class HoughTransform

{

public static ArrayData houghTransform(ArrayData inputData, int thetaAxisSize, int rAxisSize, int minContrast)

{

int width = inputData.width;

int height = inputData.height;

int maxRadius = (int)Math.ceil(Math.hypot(width, height));

int halfRAxisSize = rAxisSize >>> 1;

ArrayData outputData = new ArrayData(thetaAxisSize, rAxisSize);

// x output ranges from 0 to pi

// y output ranges from -maxRadius to maxRadius

double[] sinTable = new double[thetaAxisSize];

double[] cosTable = new double[thetaAxisSize];

for (int theta = thetaAxisSize - 1; theta >= 0; theta--)

{

double thetaRadians = theta * Math.PI / thetaAxisSize;

sinTable[theta] = Math.sin(thetaRadians);

cosTable[theta] = Math.cos(thetaRadians);

}

for (int y = height - 1; y >= 0; y--)

{

for (int x = width - 1; x >= 0; x--)

{

if (inputData.contrast(x, y, minContrast))

{

for (int theta = thetaAxisSize - 1; theta >= 0; theta--)

{

double r = cosTable[theta] * x + sinTable[theta] * y;

int rScaled = (int)Math.round(r * halfRAxisSize / maxRadius) + halfRAxisSize;

outputData.accumulate(theta, rScaled, 1);

}

}

}

}

return outputData;

}

public static class ArrayData

{

public final int[] dataArray;

public final int width;

public final int height;

public ArrayData(int width, int height)

{

this(new int[width * height], width, height);

}

public ArrayData(int[] dataArray, int width, int height)

{

this.dataArray = dataArray;

this.width = width;

this.height = height;

}

public int get(int x, int y)

{ return dataArray[y * width + x]; }

public void set(int x, int y, int value)

{ dataArray[y * width + x] = value; }

public void accumulate(int x, int y, int delta)

{ set(x, y, get(x, y) + delta); }

public boolean contrast(int x, int y, int minContrast)

{

int centerValue = get(x, y);

for (int i = 8; i >= 0; i--)

{

if (i == 4)

continue;

int newx = x + (i % 3) - 1;

int newy = y + (i / 3) - 1;

if ((newx < 0) || (newx >= width) || (newy < 0) || (newy >= height))

continue;

if (Math.abs(get(newx, newy) - centerValue) >= minContrast)

return true;

}

return false;

}

public int getMax()

{

int max = dataArray[0];

for (int i = width * height - 1; i > 0; i--)

if (dataArray[i] > max)

max = dataArray[i];

return max;

}

}

public static ArrayData getArrayDataFromImage(String filename) throws IOException

{

BufferedImage inputImage = ImageIO.read(new File(filename));

int width = inputImage.getWidth();

int height = inputImage.getHeight();

int[] rgbData = inputImage.getRGB(0, 0, width, height, null, 0, width);

ArrayData arrayData = new ArrayData(width, height);

// Flip y axis when reading image

for (int y = 0; y < height; y++)

{

for (int x = 0; x < width; x++)

{

int rgbValue = rgbData[y * width + x];

rgbValue = (int)(((rgbValue & 0xFF0000) >>> 16) * 0.30 + ((rgbValue & 0xFF00) >>> 8) * 0.59 + (rgbValue & 0xFF) * 0.11);

arrayData.set(x, height - 1 - y, rgbValue);

}

}

return arrayData;

}

public static void writeOutputImage(String filename, ArrayData arrayData) throws IOException

{

int max = arrayData.getMax();

BufferedImage outputImage = new BufferedImage(arrayData.width, arrayData.height, BufferedImage.TYPE_INT_ARGB);

for (int y = 0; y < arrayData.height; y++)

{

for (int x = 0; x < arrayData.width; x++)

{

int n = Math.min((int)Math.round(arrayData.get(x, y) * 255.0 / max), 255);

outputImage.setRGB(x, arrayData.height - 1 - y, (n << 16) | (n << 8) | 0x90 | -0x01000000);

}

}

ImageIO.write(outputImage, "PNG", new File(filename));

return;

}

public static void main(String[] args) throws IOException

{

ArrayData inputData = getArrayDataFromImage(args[0]);

int minContrast = (args.length >= 4) ? 64 : Integer.parseInt(args[4]);

ArrayData outputData = houghTransform(inputData, Integer.parseInt(args[2]), Integer.parseInt(args[3]), minContrast);

writeOutputImage(args[1], outputData);

return;

}

}</lang>

[[Image:JavaHoughTransform.png|640px480px|thumb|right|Output from example pentagon image]]'''Example use:'''

<pre>java HoughTransform pentagon.png JavaHoughTransform.png 640 480 100</pre>