problem on Android Mode, and Fixed

[PandaBalls]

while using dithering method on processing Android mode. catch wrong of PImage.set().
You can't use any calculate in PImage.set(). so i fixed like this:

public PImage imgDithering(PImage src) {
int s = 1;
for (int x = s; x < src.width-s; x+=s) {
for (int y = s; y < src.height-s; y+=s) {
color oldpixel = src.get(x, y);
color newpixel = findClosestColor(oldpixel);
float quant_error = brightness(oldpixel) - brightness(newpixel);
color oldpixel1 = src.get(x+s, y);
color oldpixel2 = src.get(x-s, y+s);
color oldpixel3 = src.get(x, y+s);
color oldpixel4 = src.get(x+s, y+s);
color newpixel1 = color(brightness(oldpixel1)+7.0/16 * quant_error);
color newpixel2 = color(brightness(oldpixel2) + 3.0/16 * quant_error);
color newpixel3 = color(brightness(oldpixel3) + 3.0/16 * quant_error);
color newpixel4 = color(brightness(oldpixel4) + 3.0/16 * quant_error);

    src.set(x, y, newpixel);
    int xnew = x+s;
    src.set(xnew, y, newpixel1);
    xnew = x-s;
    int ynew = y+s;
    src.set(xnew, ynew, newpixel2);
    ynew = y+s;
    src.set(x, ynew, newpixel3 );
    xnew = x+s;
    ynew = y+s;
    src.set(xnew, ynew, newpixel4);

}

}
src.updatePixels();
return src;
}

color findClosestColor(color c) {
color r;

if (brightness(c) < 128) {
r = color(0);
} else {
r = color(255);
}
return r;
}