CODEWITHSUNDEEP
javaimageimage-processing
user1167596
user1167596

Reputation: 107

Getting the variance and standard deviation from RGB values Java image processing

So here is my code for getting the variance (and standard deviation) of red colour values. I have done the same for Green and Blue. 

    /*Red Variance*/
    public static double varianceRed(BufferedImage image){
        Color r = new Color(image.getRGB(0, 0));
        double mean = meanValueRed(image);
        double sumOfDiff = 0.0;

         for (int y = 0; y < image.getHeight(); ++y){
               for (int x = 0; x < image.getWidth(); ++x){
                               double colour = r.getRed() - mean;
                               sumOfDiff += Math.pow(colour, 2); 
                             }                   
                           }
        return sumOfDiff / ((image.getWidth() * image.getHeight()) - 1);
        }

    /*Red Standard Deviation*/
    public static double standardDeviationRed(BufferedImage image){
        return Math.sqrt(varianceRed(image));
    }

My problem is, that each method for r,g,b returns back a variance of 0.0 and I really just can't wrap my head around why. I have done the same for the mean brightness value using Java's raster and it works fine. Now I can't understand why colour is not working. I have tried everything. Any idea as to why I am getting 0.0 and how It could be fixed?

Upvotes: 0

Views: 2132

Answers (1)

Harald K
Harald K

Reputation: 27114

You need to get the pixel of every color inside the loop, not just the one at (0,0):

public static double varianceRed(BufferedImage image) {
    double mean = meanValueRed(image);
    double sumOfDiff = 0.0;

    for (int y = 0; y < image.getHeight(); ++y) {
        for (int x = 0; x < image.getWidth(); ++x) {
             Color r = new Color(image.getRGB(x, y)); // Moved inside loop, with proper indexes
             double colour = r.getRed() - mean;
             sumOfDiff += Math.pow(colour, 2); 
         }
    }

    return sumOfDiff / ((image.getWidth() * image.getHeight()) - 1);
}

PS: You also seem to have a bug in your code for images of size 1x1. ;-)

Upvotes: 1

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