Convert 2D binary matrix to black/white image in java

Question

I am new for java. I have 2D binary matrix with only 1s and 0s now. I want to save it as jpg image(black and white) with same width and height. How could I realize that? I tried the code below but failed, saying "java.lang.IllegalArgumentException: image == null!" Please help me with that or give me your better solution. Thank you very much.

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

    //result is double[25][33] binary matrix with only 1s and 0s;
    int height=result.length;
    int width=result[0].length;;
    byte[] data = new byte[height*width];
    int k=0;
    for(int i = 0;i < height;i++){
        for(int j = 0; j < width; j++){
            data[k]=(byte)result[i][j];
            k++;
        }
        System.out.print("\n");
    }
    InputStream input = new ByteArrayInputStream(data);
    BufferedImage output = ImageIO.read(input);
    ImageIO.write(ouput, "jpg", new File("c:/result.jpg"));

}

Answer 1

This is a simple example that creates a 30x30 checkered box:

public static void main(String... args) throws IOException {
    int w = 30, h = 30;

    // create the binary mapping
    byte BLACK = (byte)0, WHITE = (byte)255;
    byte[] map = {BLACK, WHITE};
    IndexColorModel icm = new IndexColorModel(1, map.length, map, map, map);

    // create checkered data
    int[] data = new int[w*h];
    for(int i=0; i<w; i++)
        for(int j=0; j<h; j++)
            data[i*h + j] = i%4<2 && j%4<2 || i%4>=2 && j%4>=2 ? BLACK:WHITE;

    // create image from color model and data
    WritableRaster raster = icm.createCompatibleWritableRaster(w, h);
    raster.setPixels(0, 0, w, h, data);
    BufferedImage bi = new BufferedImage(icm, raster, false, null);

    // output to a file
    ImageIO.write(bi, "jpg", new File("C:\\Users\\user\\Desktop\\test.jpg"));
}

---

EDIT:

For what you are doing you actually don't need to create your own ImageColorModel, you can use a built in type: BufferedImage.TYPE_BYTE_GRAY or TYPE_BYTE_BINARY. Here is a better example and shows how to use grayscale to get a checkered box:

public static void main(String... args) throws IOException {
    int w = 40, h = 40, divs = 5;

    BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
    WritableRaster raster = bi.getRaster();

    for(int i=0; i<w; i++)
        for(int j=0; j<h; j++)
            raster.setSample(i,j,0,128+(int)(127*Math.sin(Math.PI*i/w*divs)*Math.sin(Math.PI*j/h*divs)));

    ImageIO.write(bi, "jpg", new File("C:\\Users\\user\\Desktop\\test.jpg"));
}