I'm trying to implement Floyd Steinberg algorithm in Java, working with java.awt.image.BufferedImage.
I've used the algorithm described here with a custom palette, and I was expecting to get more or less the same image as in the wikipedia example (or as generated by Gimp for example), but I get a very different version.
You can see what I get
I'm obviously missing something (output image has color which doesn't belong to my palette), but I can't figure out what.
What I'm doing wrong ?
Here's the code :
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.IndexColorModel;
import java.io.File;
import java.io.IOException;
public class FloydSteinbergTest {
private static final Color[] PALETTE = new Color[]{
new Color(221, 221, 221),
new Color(19, 125, 62),
new Color(179, 80, 188),
new Color(107, 138, 201),
new Color(177, 166, 39),
new Color(65, 174, 56),
new Color(208, 132, 153),
new Color(64, 64, 64),
new Color(154, 161, 161),
new Color(46, 110, 137),
new Color(126, 61, 181),
new Color(46, 56, 141),
new Color(79, 50, 31),
new Color(53, 70, 27),
new Color(150, 52, 48),
new Color(25, 22, 22)};
public static void main(String[] args) {
String lImgFile = "/tmp/test.jpg";
try {
// Load image
BufferedImage lImage = ImageIO.read(new File(lImgFile));
BufferedImage lOutImage = applyDitheredPalette(lImage, PALETTE);
ImageIO.write(lOutImage, "png", new File("/tmp/out.png"));
} catch (IOException lEx) {
System.out.println(lEx.getMessage());
}
}
/**
* @param pPalette Color palette to apply.
* @param pImage Image to apply palette on.
* @return {@link java.awt.image.BufferedImage} corresponding to pPalette applied on pImage using naive Floyd-Steinberg implementation
*/
public static BufferedImage applyDitheredPalette(BufferedImage pImage, Color[] pPalette) {
int lWidth = pImage.getWidth();
int lHeight = pImage.getHeight();
IndexColorModel lColorModel = paletteToColorModel(pPalette);
BufferedImage lImageOut = new BufferedImage(lWidth, lHeight, BufferedImage.TYPE_BYTE_INDEXED, lColorModel);
for (int y = (lHeight - 1); y >= 0; y--) {
for (int x = 0; x < lWidth; x++) {
// Get original pixel color channels
int lInitialPixelColor = pImage.getRGB(x, y);
// Finding nearest color in the palette
Color lNearestColor = getNearestColor(lInitialPixelColor, pPalette);
// Set quantized pixel
lImageOut.setRGB(x, y, lNearestColor.getRGB());
// Applying Floyd-Steinberg dithering
int quantizationError = lInitialPixelColor - lNearestColor.getRGB();
if ((x + 1) < lWidth) {
int lPixel = pImage.getRGB(x + 1, y);
lImageOut.setRGB(x + 1, y, lPixel + (quantizationError * (7 / 16)));
}
if ((x - 1) > 0 && (y + 1) < lHeight) {
int lPixel = pImage.getRGB(x - 1, y + 1);
lImageOut.setRGB(x - 1, y + 1, lPixel + (quantizationError * (3 / 16)));
}
if ((y + 1) < lHeight) {
int lPixel = pImage.getRGB(x, y + 1);
lImageOut.setRGB(x, y + 1, lPixel + (quantizationError * (5 / 16)));
}
if ((x + 1 < lWidth) && (y + 1 < lHeight)) {
int lPixel = pImage.getRGB(x + 1, y + 1);
lImageOut.setRGB(x + 1, y + 1, lPixel + (quantizationError * (1 / 16)));
}
// End of Floyd-Steinberg dithering
}
}
return lImageOut;
}
/**
* @param pPalette to load color model from
* @return {@link java.awt.image.IndexColorModel} Color model initialized using pPalette colors
*/
private static IndexColorModel paletteToColorModel(Color[] pPalette) {
int lSize = pPalette.length;
// Getting color component for each palette color
byte[] lReds = new byte[lSize];
byte[] lGreens = new byte[lSize];
byte[] lBlues = new byte[lSize];
for (int i = 0; i < lSize; i++) {
Color lColor = pPalette[i];
lReds[i] = (byte) lColor.getRed();
lGreens[i] = (byte) lColor.getGreen();
lBlues[i] = (byte) lColor.getBlue();
}
return new IndexColorModel(4, lSize, lReds, lGreens, lBlues);
}
/**
* @param pColor Color to approximate
* @param pPalette Color palette to use for quantization
* @return {@link java.awt.Color} nearest from pColor value took in pPalette
*/
private static Color getNearestColor(int pColor, Color[] pPalette) {
Color lNearestColor = null;
double lNearestDistance = Integer.MAX_VALUE;
double lTempDist;
for (Color lColor : pPalette) {
Color lRgb = new Color(pColor);
lTempDist = distance(lRgb.getRed(), lRgb.getGreen(), lRgb.getBlue(), lColor.getRed(), lColor.getGreen(), lColor.getBlue());
if (lTempDist < lNearestDistance) {
lNearestDistance = lTempDist;
lNearestColor = lColor;
}
}
return lNearestColor;
}
/**
* @return Distance between 2 pixels color channels.
*/
private static double distance(int pR1, int pG1, int pB1, int pR2, int pG2, int pB2) {
double lDist = Math.pow(pR1 - pR2, 2) + Math.pow(pG1 - pG2, 2) + Math.pow(pB1 - pB2, 2);
return Math.sqrt(lDist);
}}
