Change the color of each pixel in an image java

Question

I wanna change different pixel to different color. Basically, change part of pixel to transparent.

for(int i = 0; i < image.getWidth();i++)
        for(int j = 0; j < image.getHeight(); j ++)
        {
            image.setRGB(i,j , 0);
        }

//I aslo change the third parameter 0 to another attribute. but it still does not work. it all show black. do you have some ideas?

yin. thanks

class ImagePanel extends JPanel {

    private BufferedImage image;

    public ImagePanel(int width, int height, BufferedImage image) {
        this.image = image;
        image = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_ARGB);
        repaint();
    }

    /**
     * Draws the image.
     */

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (int i = 0; i < image.getWidth(); i++) {
            for (int j = 0; j < image.getHeight(); j++) {
                image.setRGB(i, j, 0);
            }
        }
        g.drawImage(image, 0, 0, getWidth(), getHeight(), this);

    }

}

the image is a bufferedImage and i out it into a frame. i wanna change partial transparency of the image — Huazhe Yin, Nov 23 '14 at 15:11

Adam · Accepted Answer · 2014-11-26T22:25:56.560

The third parameter is ARGB value in 32 bits. This is laid out in bit form as:

AAAAAAAA|RRRRRRRR|GGGGGGGG|BBBBBBBBB

See the javadoc for BufferedImage.setRGB (assuming your using BufferedImage, your question doesn't actually say...)

Sets a pixel in this BufferedImage to the specified RGB value. The pixel is assumed to be in the default RGB color model, TYPE_INT_ARGB, and default sRGB color space. For images with an IndexColorModel, the index with the nearest color is chosen

If you're using an image type that supports transparency it is important you set alpha 255 means fully opaque, 0 is fully transparent.

You can create such a value using bit shifting.

int alpha = 255; 
int red   = 0;
int green = 255;
int blue  = 0;

int argb = alpha << 24 + red << 16 + green << 8 + blue

image.setRGB(i, j, argb);

Luckily there is a getRGB() method on java.awt.Color instances, so you could use

image.setRGB(i, j, Color.green.getRGB());

Here's a full working example, perhaps you can compare to your code:

public class StackOverflow27071351 {
    private static class ImagePanel extends JPanel {
        private BufferedImage image;
        public ImagePanel(int width, int height, BufferedImage image) {
            this.image = image;
            image = new BufferedImage(width, height,
                    BufferedImage.TYPE_INT_ARGB);
            repaint();
        }
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (int i = 0; i < image.getWidth(); i++) {
                for (int j = 0; j < image.getHeight(); j++) {
                    image.setRGB(i, j, new Color(255, 0, 0, 127).getRGB());
                }
            }
            g.drawImage(image, 0, 0, getWidth(), getHeight(), this);
        }
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        int width = 640;
        int height = 480;
        frame.setSize(width, height);
        BufferedImage image = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_ARGB);
        frame.getContentPane().setLayout(new BorderLayout());
        frame.getContentPane().add(new ImagePanel(width, height, image));
        frame.setVisible(true);
    }
}

Thanks for answering. I use BufferedImage, and i try in ur way. but it doesn't work either. i use a black image( an image with all black background). — Huazhe Yin, Nov 23 '14 at 14:28
Can you post your code to create bufferedimage and display it — Adam, Nov 23 '14 at 17:59
@HuazheYin I've added a fully working example showing red, I've not seen the all black problem you describe... — Adam, Nov 26 '14 at 22:28

score 2 · Answer 2 · answered Nov 21 '14 at 22:26

2

Well, 3rd parameter is the color in RGB, so it will be black if you set it to 0.

answered Nov 21 '14 at 22:26

striving_coder

798
1
5
7

score 1 · Answer 3 · answered Nov 21 '14 at 22:30

1

here is a sample code:

private int colorToRGB(int alpha, int red, int green, int blue) {
        int newPixel = 0;
        newPixel += alpha;
        newPixel = newPixel << 8;
        newPixel += red;
        newPixel = newPixel << 8;
        newPixel += green;
        newPixel = newPixel << 8;
        newPixel += blue;

        return newPixel;
    }

then

image.setRGB(i, j, colorToRGB(alpha, 0, 0, 0))

answered Nov 21 '14 at 22:30

Ammar

719
6
21

thanks for answering. what is the alpha, what value should i pass to it? – Huazhe Yin Nov 23 '14 at 14:30
the alpha value is between 0(transparent) -> 255, don't forget as @Adam mentioned to set your BufferedImage to TYPE_INT_ARGB – Ammar Nov 23 '14 at 14:42
i just tried it, it still does not work. my program is simple, i just put a buffered image into a frame and i can change the frame transparency, but i wanna change the partial transparency. do u have more resolution? – Huazhe Yin Nov 23 '14 at 15:07
if you just want to change frame transparency I recommend to use AlphaComposite. Check this: http://www.java2s.com/Code/Java/2D-Graphics-GUI/MakeimageTransparency.htm – Ammar Nov 23 '14 at 15:14
i know how to change the transparency of a frame, and i implement it. it can change the whole transparency of frame, but my requirement is change partial transparency, thats why i use buffered image. so i change the partial transparency of frame by changing the partial transparency of buffered image. – Huazhe Yin Nov 23 '14 at 15:48

Phil Freihofner · Answer 4 · 2014-11-21T22:55:19.823

I use the following form:

int[] pixel = new int[4];

// the following four ints must range 0..255
pixel[0] = redValue;
pixel[1] = greenValue;
pixel[2] = bluleValue;
pixel[3] = alphaValue;

raster.setPixel(x, y, pixel);

To get a raster for a BufferedImage, I do this:

BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
WritableRaster raster = image.getRaster();

I've done some performance testing, and have not found that stuffing all the bytes of color values into a single number to make much of a difference.

It is also good to know the technique where one can draw an opaque image (e.g., RGB rather than an ARGB) with an alpha value.

g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, (float) (yourAlpha)));
g2d.drawImage(...);

Change the color of each pixel in an image java

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