CODEWITHSUNDEEP
c++imagemultidimensional-array
H.C
H.C

Reputation: 9

Quantize an image

My instructor wrote "Write a function that quantizes the image to q grayscale shades. For example, if q=8, replace each pixel between 0-31 by 0, 32-63 by 32, ..., and 224-255 by 224." This is my code so far.

void quantize (int image[][MAXHEIGHT], int width, int height, int q)
{
    const int temp = 256 / q;

    int startPixel, endPixel;
    int indicator = temp; // where the pixels are divided, 0-31, 32-63, etc if q = 8

    while (indicator <= 256)
    {
        startPixel = indicator - temp;
        endPixel = indicator - 1;
        cout << "start value is " << startPixel << " and end value is " << endPixel << endl;

        for (int row = 0; row < height; row++)
        {
            for (int col = 0; col < width; col++)
            {
                if ((image[col][row] > startPixel) && (image[col][row] <= endPixel));
                {
                    image[col][row] = startPixel;
                }
            }
        }

        indicator += temp;
    }
}

When I try to quantize an image it either turns completely white or completely black. I think I'm looping this function wrong but not sure what to do to fix it.

Upvotes: 0

Views: 3025

Answers (1)

Javier
Javier

Reputation: 341

The error is in the header of your function. You are passing a copy of your image, so your copy is modified inside your function, but not out of the function. Moreover, the code could be simplified a lot. I give you my approach:

void quantize (int **image, int width, int height, int q)
{
   const int r = 256 / q; // Ensure your image is on [0 255] range 
   for (int row = 0; row < height; row++)
      for (int col = 0; col < width; col++)
         image[col][row] = (int) (image[col][row] / r);
}

Upvotes: 2

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