Histogram in Java

Question

Hello,

I need to transform an image into a pixel array.

For example: Given the image "Netuno.jpeg", of 256 x 256 pixels, I need to allocate the value of pixels in that Matrix and print the amount that these pixels appear in another vector:

Matrix[0][0] = 2 (where 2 is the pixel value),

Matrix[0][1] = 12, ... , Matrix[255][255] = 23

Qtd of pixels 0 = 34 (34 being the number of times the pixel of value 0 appeared) ,

Qtd of pixels 1 = 21, ... , Qtd of pixels 255 = 120

So far I have read the image using Bufferedimage, but do not know how to access the image pixels.

import xxx;

public class Histograma {

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

    //Atributos

    //Métodos

    //Leitura da Imagem - Planeta Netuno

    BufferedImage img = ImageIO.read(new File("/home/patch/netuno.jpeg"));
    int altura = img.getHeight();
    int largura = img.getWidth();
    int[][] matrix = new int[largura][altura];

    for(int i = 0; i < img.getWidth(); i++) {
        for(int j = 0; j < img.getHeight(); j++) {

        }
    }           
}   

Thank you!

Answer 1

Reading the class documentation Bufferedimage, it seems to me that you can read the RGB value of each pixel at position (x, y), this value which is returned as a int. The name of the method is getRGB(int x, int y). Once the RGB value is obtained, you can break it into the red, green and blue components by applying a little bit of bit brushing, if necessary. Or just use it as an index for your histogram.