How do I make the for loops for this code? (I need to check a region of an image for a certain color.)

Question

According to Get color of each pixel of an image using BufferedImages, the following code needs for loops for its intended purpose to work.

public class GetPixelColor
{
  public static void main(String args[]) throws IOException{
  File file= new File("your_file.jpg");
  BufferedImage image = ImageIO.read(file);
  // Getting pixel color by position x and y 
  int clr=  image.getRGB(x,y); 
  int  red   = (clr & 0x00ff0000) >> 16;
  int  green = (clr & 0x0000ff00) >> 8;
  int  blue  =  clr & 0x000000ff;
  System.out.println("Red Color value = "+ red);
  System.out.println("Green Color value = "+ green);
  System.out.println("Blue Color value = "+ blue);
  }
}

How do I define the region of the image I would like to check for its color with for loops?

https://www.developer.com/java/data/using-different-types-of-java-loops-looping-in-java.html — Quintium, Jan 08 '18 at 19:57

score 1 · Accepted Answer · answered Jan 08 '18 at 20:10

1

the region you want to read it's color is a rectangle between two points p1(x1,y1), p2(x2,y2) and you scan that rectangle by two nested for loops like this

for(int x=x1; x<=x2; x++)
   for(int y=y1; y<=y2; y++){
        // Getting pixel color by position x and y 
        int clr=  image.getRGB(x,y); 
        int  red   = (clr & 0x00ff0000) >> 16;
        int  green = (clr & 0x0000ff00) >> 8;
        int  blue  =  clr & 0x000000ff;
        System.out.println("Red Color value = "+ red);
        System.out.println("Green Color value = "+ green);
        System.out.println("Blue Color value = "+ blue);
   }

answered Jan 08 '18 at 20:10

Hassan

407
5
22

1

I know this was not part of the original question but can you help me understand what is going on in "int red = (clr & 0x00ff0000) >> 16;" If I understand correctly, "clr & 0x00ff0000" is a boolean value. It is even shifted ">>16". How can this be assigned to an integer? – user9157181 Jan 09 '18 at 19:39
`&` is the logical `AND` operation, the boolean operator is `&&`, what the code dose is masking the `red` value from the `clr` and then shift it `>> 16` – Hassan Jan 09 '18 at 20:02

score 0 · Answer 2 · answered Jan 08 '18 at 20:06

You can simply use two nested for loops to loop through the image, something like this:

public static void printPixelColors(BufferedImage img) {
        int imageWidth = img.getWidth();
        int imageHeight = img.getHeight();
        for (int y = 0; y < imageHeight; y++) {
            for (int x = 0; x < imageWidth; x++) {
                // Getting pixel color by position x and y 
                int clr = img.getRGB(x, y);
                int red = (clr & 0x00ff0000) >> 16;
                int green = (clr & 0x0000ff00) >> 8;
                int blue = clr & 0x000000ff;
                System.out.println("Red Color value = " + red);
                System.out.println("Green Color value = " + green);
                System.out.println("Blue Color value = " + blue);
            }
        }
 }

How do I make the for loops for this code? (I need to check a region of an image for a certain color.)

2 Answers2