CODEWITHSUNDEEP
javaimage-processing
Daniel Braithwaite
Daniel Braithwaite

Reputation: 185

How to take a group of pixels and combine them into one

Im trying to create a program that finds images that are similar to each other and i found a site ( http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html ) that gives steps for making a function that creates a fingerprint of an image, the first step is to reduce the size of the image to a 8 by 8 ( 64 pixel ) image, but i cant figure out how to convert a group of pixels into one pixel e.g. 

[(R,G,B)][(R,G,B)][(R,G,B)]
[(R,G,B)][(R,G,B)][(R,G,B)]
[(R,G,B)][(R,G,B)][(R,G,B)]

take this group of pixels, each pixel has a diffrent R, G and B value, how can i take them all and turn them into one set of values e.g.

[(R,G,B)]

I thought maybe add all the R, G and B values up and then average them but that seemed to simple, dose anyone know how to do this ? i am writing this program in java.

Upvotes: 0

Views: 2281

Answers (1)

Constantin
Constantin

Reputation: 8961

There are a lot of different interpolation/re-sampling techniques to do downscaling - you can choose one depending on what results you're expecting. A simple one i.e. is the Nearest neighbour interpolation: But this wouldn't lead to very detailed results, due to the simplicity.

More advanced techniques i.e. linear interpolation, biliniear interpolation or bicubic interpolation are way better suitable, if the pictures are actually photos (rather than i.e. pixelart). But the downscaled image in the link hasn't much details left either - so Nearest neighbor seems quite sufficient (at least to start with).

public int[] resizePixels(int[] pixels,int w1,int h1,int w2,int h2) {
    int[] temp = new int[w2*h2] ;
    double x_ratio = w1/(double)w2 ;
    double y_ratio = h1/(double)h2 ;
    double px, py ; 
    for (int i=0;i<h2;i++) {
        for (int j=0;j<w2;j++) {
            px = Math.floor(j*x_ratio) ;
            py = Math.floor(i*y_ratio) ;
            temp[(i*w2)+j] = pixels[(int)((py*w1)+px)] ;
        }
    }
    return temp ;
}

This java function takes an array of pixel values (original size - w1 and h1) and returns an nearest neighbour (up/down)-scaled array of pixels with dimensions w2 x h2. See also: here.

Upvotes: 1

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