Convert Short [] to Halftone

Question

I am writing a Buddhabrot fractal generator using aparapi. I got the OpenCL part to work, the result is a one-dimensional array that represents each pixel. I have the size of the final image as the final ints, and I wrote code to get the index of arbitrary points in this array. I want to save this as an image, and I'm trying to use BufferedImage with TYPE_USHORT_GRAY. Here is what I still have:

BufferedImage image=new BufferedImage(VERTICAL_PIXELS, HORIZONTAL_PIXELS, BufferedImage.TYPE_USHORT_GRAY); for(int i=0; i<VERTICAL_PIXELS; i++) for(int k=0; k<HORIZONTAL_PIXELS; k++) image.setRGB(k, i, normalized[getArrayIndex(k,i,HORIZONTAL_PIXELS)]); 

The problem is that I do not know how to set RGB. What do I need to do?

Answer 1

The problem is that setRGB() requires a color value of 0xRRGGBB. BufferedImage loves pretending to be an RGB image, no matter what data is stored. In fact, you can get the internal DataBufferShort (with getTile(0, 0).getDataBuffer() ), but it can be difficult to determine how it is laid out.

If you already have pixels in short[] , a simpler solution would be to copy them to int[] instead of shooting it in a MemoryImageSource :

 int[] buffer = /* pixels */; ColorModel model = new ComponentColorModel( ColorSpace.getInstance(ColorSpace.CS_GRAY), new int[] { 16 }, false, true, Transparency.OPAQUE, DataBuffer.TYPE_USHORT); Image image = Toolkit.getDefaultToolkit().createImage( new MemoryImageSource(VERTICAL_PIXELS, HORIZONTAL_PIXELS, model, buffer, 0, VERTICAL_PIXELS)); 

The advantage of this approach is that you control the underlying array of pixels. You can make changes to this array and call newPixels() on your MemoryImageSource , and it will be updated in real time. It also gives you full power to define your own palette, except for shades of gray:

 int[] cmap = new int[65536]; for(int i = 0; i < 65536; ++i) { cmap[i] = (((i % 10000) * 256 / 10000) << 16) | (((i % 20000) * 256 / 20000) << 8) | (((i % 40000) * 256 / 40000) << 0); } ColorModel model = new IndexColorModel(16, 65536, cmap, 0, false, -1, DataBuffer.TYPE_USHORT); 

This approach works fine if you just want to display the image on the screen:

 JFrame frame = new JFrame(); frame.getContentPane().add(new JLabel(new ImageIcon(image))); frame.pack(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); 

However, if you want to write it to a file and save the format with one short pixel (say, upload to Matlab), you're out of luck. The best you can do is draw it in a BufferedImage and save it using ImageIO , which will be saved as RGB.

If you definitely need a BufferedImage at the end, another approach is to apply the color palette yourself, calculate the RGB values ​​and then copy them to the image:

 short[] data = /* your data */; int[] cmap = /* as above */; int[] rgb = new int[data.length]; for(int i = i; i < rgb.length; ++i) { rgb[i] = cmap[data[i]]; } BufferedImage image = new BufferedImage( VERTICAL_PIXELS, HORIZONTAL_PIXELS, BufferedImage.TYPE_INT_RGB); image.setRGB(0, 0, VERTICAL_PIXELS, HORIZONTAL_PIXELS, pixels, 0, VERTICAL_PIXELS); 

Answer 2

For reference, this example shows how two different types of BufferedImage interpret the same 16-bit data. You can hover over images to see pixel values.

Appendix: To explain the interpretation of the word in detail, note that setRGB() tries to find the closest match to the specified value in the given ColorModel .

 import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.GridLayout; import java.awt.Point; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.image.BufferedImage; import java.util.Random; import javax.swing.JFrame; import javax.swing.JPanel; /** @see http://stackoverflow.com/questions/8765004 */ public class BufferedImageTest extends JPanel { private static final int SIZE = 256; private static final Random r = new Random(); private final BufferedImage image; public BufferedImageTest(int type) { image = new BufferedImage(SIZE, SIZE, type); this.setPreferredSize(new Dimension(SIZE, SIZE)); for (int row = 0; row < SIZE; row++) { for (int col = 0; col < SIZE; col++) { image.setRGB(col, row, 0xff00 << 16 | row << 8 | col); } } this.addMouseMotionListener(new MouseAdapter() { @Override public void mouseMoved(MouseEvent e) { Point p = e.getPoint(); int x = px * SIZE / getWidth(); int y = py * SIZE / getHeight(); int c = image.getRGB(x, y); setToolTipText(x + "," + y + ": " + String.format("%08X", c)); } }); } @Override protected void paintComponent(Graphics g) { g.drawImage(image, 0, 0, getWidth(), getHeight(), null); } static private void display() { JFrame f = new JFrame("BufferedImageTest"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.setLayout(new GridLayout(1, 0)); f.add(new BufferedImageTest(BufferedImage.TYPE_INT_ARGB)); f.add(new BufferedImageTest(BufferedImage.TYPE_USHORT_GRAY)); f.pack(); f.setLocationRelativeTo(null); f.setVisible(true); } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { @Override public void run() { display(); } }); } }