private PixImage GetSubImage(int x, int y, int width, int height)
{
PixImage newImage = new PixImage(width, height);
for (int i = x; i < x + width; i++)
{
for (int j = y; j < y + height; j++)
{
newImage.setPixel(i - x, j - y, this.getRed(i, j), this.getGreen(i, j), this.getBlue(i, j));
}
}
return(newImage);
}
/// <summary>
/// array2PixImage() converts a 2D array of grayscale intensities to
/// a grayscale PixImage.
/// </summary>
/// <param name="pixels"> a 2D array of grayscale intensities in the range 0...255. </param>
/// <returns> a new PixImage whose red, green, and blue values are equal to
/// the input grayscale intensities. </returns>
private static PixImage array2PixImage(int[][] pixels)
{
int width = pixels.Length;
int height = pixels[0].Length;
PixImage image = new PixImage(width, height);
for (int x = 0; x < width; x++)
{
for (int y = 0; y < height; y++)
{
image.setPixel(x, y, (short)pixels[x][y], (short)pixels[x][y], (short)pixels[x][y]);
}
}
return(image);
}
//this helper function returns a new PixImage with pixels on the edges reflected across the axis
//so that each pixel in the original image has 9 neighbors (including itself)
private PixImage GetReflection()
{
var newMatrix = new PixImage(Width + 2, Height + 2);
for (int x = 1; x < newMatrix.Width - 1; x++)
{
for (int y = 1; y < newMatrix.Height - 1; y++)
{
newMatrix.setPixel(x, y, this.getRed(x - 1, y - 1), this.getGreen(x - 1, y - 1), this.getBlue(x - 1, y - 1));
}
}
for (int x = 0; x < newMatrix.Width; x++)
{
for (int y = 0; y < newMatrix.Height; y++)
{
int a = x;
int b = y;
short red = 0;
if (x == 0)
{
a = 1;
}
if (y == 0)
{
b = 1;
}
if (x == newMatrix.Width - 1)
{
a = newMatrix.Width - 2;
}
if (y == newMatrix.Height - 1)
{
b = newMatrix.Height - 2;
}
red = (short)newMatrix.getRed(a, b);
//Console.WriteLine("getting a: {0}, b: {1}, for x: {2}, y: {3} which is: {4}", a, b, x, y, red);
newMatrix.setPixel(x, y, red, red, red);
}
}
//Console.WriteLine(newMatrix);
return(newMatrix);
}
/// <summary>
/// sobelEdges() applies the Sobel operator, identifying edges in "this"
/// image. The Sobel operator computes a magnitude that represents how
/// strong the edge is. We compute separate gradients for the red, blue, and
/// green components at each pixel, then sum the squares of the three
/// gradients at each pixel. We convert the squared magnitude at each pixel
/// into a grayscale pixel intensity in the range 0...255 with the logarithmic
/// mapping encoded in mag2gray(). The output is a grayscale PixImage whose
/// pixel intensities reflect the strength of the edges.
///
/// See http://en.wikipedia.org/wiki/Sobel_operator#Formulation for details.
/// </summary>
/// <returns> a grayscale PixImage representing the edges of the input image.
/// Whiter pixels represent stronger edges. </returns>
public virtual PixImage SobelEdges()
{
var newImage = new PixImage(this.Width, this.Height);
//constant, Sobel operator
int[,] xSobelOperator =
{
{ 1, 0, -1 },
{ 2, 0, -2 },
{ 1, 0, -1 }
};
//constant, Sobel operator
int[,] ySobelOperator =
{
{ 1, 2, 1 },
{ 0, 0, 0 },
{ -1, -2, -1 }
};
int[] gx, gy;
long[,] energy = new long[Width, Height];
//get reflection so every pixel within the original image has 9 neighbors (incl itself)
var newImageWithReflection = this.GetReflection();
//traverse each pixel within original image and calculate dot product
for (int i = 0; i < Width; i++)
{
for (int j = 0; j < Height; j++)
{
//get subimage for each pixel (from newImageWithReflection)
var image = newImageWithReflection.GetSubImage(i, j, 3, 3);
//calculate dot product with x and y sobel operators
gx = image.DotProduct(xSobelOperator);
gy = image.DotProduct(ySobelOperator);
//calculate energy values
energy[i, j] = (gx[0] * gx[0]) + (gy[0] * gy[0]) + (gx[1] * gx[1]) + (gy[1] * gy[1]) + (gx[2] * gx[2]) + (gy[2] * gy[2]);
newImage.setPixel(i, j, mag2gray(energy[i, j]), mag2gray(energy[i, j]), mag2gray(energy[i, j]));
}
}
return(newImage);
}
/// <summary>
/// equals() checks whether two images are the same, i.e. have the same
/// dimensions and pixels.
/// </summary>
/// <param name="image"> a PixImage to compare with "this" PixImage. </param>
/// <returns> true if the specified PixImage is identical to "this" PixImage. </returns>
public virtual bool Equals(PixImage image)
{
int width = Width;
int height = Height;
if (image == null || width != image.Width || height != image.Height)
{
return(false);
}
for (int x = 0; x < width; x++)
{
for (int y = 0; y < height; y++)
{
if (!(getRed(x, y) == image.getRed(x, y) && getGreen(x, y) == image.getGreen(x, y) && getBlue(x, y) == image.getBlue(x, y)))
{
return(false);
}
}
}
return(true);
}
/// <summary>
/// boxBlur() returns a blurred version of "this" PixImage.
///
/// If numIterations == 1, each pixel in the output PixImage is assigned
/// a value equal to the average of its neighboring pixels in "this" PixImage,
/// INCLUDING the pixel itself.
///
/// A pixel not on the image boundary has nine neighbors--the pixel itself and
/// the eight pixels surrounding it. A pixel on the boundary has six
/// neighbors if it is not a corner pixel; only four neighbors if it is
/// a corner pixel. The average of the neighbors is the sum of all the
/// neighbor pixel values (including the pixel itself) divided by the number
/// of neighbors, with non-integer quotients rounded toward zero (as C# does
/// naturally when you divide two integers).
///
/// Each color (red, green, blue) is blurred separately. The red input should
/// have NO effect on the green or blue outputs, etc.
///
/// The parameter numIterations specifies a number of repeated iterations of
/// box blurring to perform. If numIterations is zero or negative, "this"
/// PixImage is returned (not a copy). If numIterations is positive, the
/// return value is a newly constructed PixImage.
///
/// IMPORTANT: DO NOT CHANGE "this" PixImage!!! All blurring/changes should
/// appear in the new, output PixImage only.
/// </summary>
/// <param name="numIterations"> the number of iterations of box blurring. </param>
/// <returns> a blurred version of "this" PixImage. </returns>
public virtual PixImage BoxBlur(int numIterations)
{
if (numIterations > 0)
{
//make a new image
var newImage = new PixImage(this.Width, this.Height);
for (int i = 0; i < this.Width; i++)
{
for (int j = 0; j < this.Height; j++)
{
Pixel newPixel = this.GetBlurredPixel(i, j);
newImage.setPixel(i, j, newPixel.Red, newPixel.Green, newPixel.Blue);
// Console.WriteLine("At pixel {0},{1}: {2}, {3}, {4}. Counter: {5}", i, j, red, green, blue, counter);
}
}
for (int n = 0; n < numIterations; n++)
{
newImage = newImage.BoxBlur(n);
}
return(newImage);
}
return(this);
}
/// <summary>
/// main() runs a series of tests to ensure that the convolutions (box blur
/// and Sobel) are correct.
/// </summary>
public static void Main(string[] args)
{
// Be forwarned that when you write arrays directly in C# as below,
// each "row" of text is a column of your image--the numbers get
// transposed.
PixImage image1 = array2PixImage(new int[][]
{
new int[] { 0, 10, 240 },
new int[] { 30, 120, 250 },
new int[] { 80, 250, 255 }
});
Console.WriteLine("Testing getWidth/getHeight on a 3x3 image. " + "Input image:");
Console.Write(image1);
doTest(image1.Width == 3 && image1.Height == 3, "Incorrect image width and height.");
Console.WriteLine("Testing blurring on a 3x3 image.");
doTest(image1.BoxBlur(1).Equals(array2PixImage(new int[][]
{
new int[] { 40, 108, 155 },
new int[] { 81, 137, 187 },
new int[] { 120, 164, 218 }
})), "Incorrect box blur (1 rep):\n" + image1.BoxBlur(1));
doTest(image1.BoxBlur(2).Equals(array2PixImage(new int[][]
{
new int[] { 91, 118, 146 },
new int[] { 108, 134, 161 },
new int[] { 125, 151, 176 }
})), "Incorrect box blur (2 rep):\n" + image1.BoxBlur(2));
doTest(image1.BoxBlur(2).Equals(image1.BoxBlur(1).BoxBlur(1)), "Incorrect box blur (1 rep + 1 rep):\n" + image1.BoxBlur(2) + image1.BoxBlur(1).BoxBlur(1));
Console.WriteLine("Testing edge detection on a 3x3 image.");
doTest(image1.SobelEdges().Equals(array2PixImage(new int[][]
{
new int[] { 104, 189, 180 },
new int[] { 160, 193, 157 },
new int[] { 166, 178, 96 }
})), "Incorrect Sobel:\n" + image1.SobelEdges());
PixImage image2 = array2PixImage(new int[][]
{
new int[] { 0, 100, 100 },
new int[] { 0, 0, 100 }
});
Console.WriteLine("Testing getWidth/getHeight on a 2x3 image. " + "Input image:");
Console.Write(image2);
doTest(image2.Width == 2 && image2.Height == 3, "Incorrect image width and height.");
Console.WriteLine("Testing blurring on a 2x3 image.");
doTest(image2.BoxBlur(1).Equals(array2PixImage(new int[][]
{
new int[] { 25, 50, 75 },
new int[] { 25, 50, 75 }
})), "Incorrect box blur (1 rep):\n" + image2.BoxBlur(1));
Console.WriteLine("Testing edge detection on a 2x3 image.");
doTest(image2.SobelEdges().Equals(array2PixImage(new int[][]
{
new int[] { 122, 143, 74 },
new int[] { 74, 143, 122 }
})), "Incorrect Sobel:\n" + image2.SobelEdges());
Console.ReadLine();
}
