small problem in posterize shader

clankill3r

I converted this posterize shader to processing: http://www.geeks3d.com/20091027/shader-library-posterization-post-processing-effect-glsl/

When i set it to 2 colors i see 3 colors:

Does it count from zero or something?

Also i found other filters like: http://hub.jmonkeyengine.org/forum/topic/posterization-post-processing-filter/ http://www.filewatcher.com/p/gluon-0.70.0.tar.gz.8234641/gluon-gluon/graphics/shaders/GLSL/posterize.frag.html So if someone is ever bored, feel free to convert them to processing so we can benchmark them.

PShader posterize; 
PImage img;
boolean enabled;

void setup() {
  size(640, 360, P2D);
  img = loadImage("leaves.jpg");     
  posterize = loadShader("posterize.glsl");

  posterize.set("gamma", 0.6);
}

void draw() {
  if (enabled) {
    posterize.set("numColors", map(mouseX, 0, width, 2, 255));
    posterize.set("gamma", map(mouseY, 0, height, 0.0, 1.0));
  }

  image(img, 0, 0);
}

void mousePressed() {
  if (enabled = !enabled) shader(posterize); else resetShader();
}

the shader:

#define PROCESSING_TEXTURE_SHADER

uniform sampler2D texture;
varying vec4 vertTexCoord;
uniform float gamma; // 0.6
uniform float numColors;

void main() {
  vec3 c = texture2D(texture, vertTexCoord.st).rgb;

  c = pow(c, vec3(gamma, gamma, gamma));
  c = c * numColors;
  c = floor(c);
  c = c / numColors;
  c = pow(c, vec3(1.0/gamma));
  gl_FragColor = vec4(c, 1.0);
}

clankill3r

More important, why does the script in the OP works. But this gives an:

OpenGL error 1282 at bot endDraw(): invalid operation

PImage img;
PShader posterize;
PGraphics pg;

void setup() {
  size(1000, 800, OPENGL);
  img = loadImage("map.gif"); 


  posterize = loadShader("posterize.glsl");
  posterize.set("gamma", 0.6);
  posterize.set("numColors", 255);

  pg = createGraphics(img.width, img.height, P2D);
  pg.beginDraw();
  pg.shader(posterize);
  pg.image(img, 0, 0);
  pg.endDraw();

  println("setup ok");

}

void draw() {
  image(pg, 0, 0);
}

clankill3r

O yeah for who wonders, this is the original processing shader filter:

case POSTERIZE:
        int levels = (int)param;
        if ((levels < 2) || (levels > 255)) {
          throw new RuntimeException("Levels must be between 2 and 255 for " +
                                     "filter(POSTERIZE, levels)");
        }
        int levels1 = levels - 1;
        for (int i = 0; i < pixels.length; i++) {
          int rlevel = (pixels[i] >> 16) & 0xff;
          int glevel = (pixels[i] >> 8) & 0xff;
          int blevel = pixels[i] & 0xff;
          rlevel = (((rlevel * levels) >> 8) * 255) / levels1;
          glevel = (((glevel * levels) >> 8) * 255) / levels1;
          blevel = (((blevel * levels) >> 8) * 255) / levels1;
          pixels[i] = ((0xff000000 & pixels[i]) |
                       (rlevel << 16) |
                       (glevel << 8) |
                       blevel);
        }
        break;