Dithering

Basic Concepts

• Problem
  • Contouring
• Solution
  • Distribute Error
• Trade-off
  • Spatial Color
• Classification
  • Pattern Type
  • Dot

Serpentine-Diffusion Dithering

Quantization Function

#define QUANT_N(V,N) ((V/(256/N))*(255/(N-1)))

Error Diffusion with Serpentine Scan

void img_dither_ds(Image *i, int n)
{
  int u, v, c, q, err = 0, w = i->w-1;

  for (v = 0; v < i->h; v++) {
    for (u = EVEN(v)? 0 : w ; u >= 0 && u <= w; u = EVEN(v)? u+1 : u-1) {
      c = img_geti(i,u,v);
      q = c + err;
      q = QUANT_N(q,n);
      q = CLAMP(q,0,255);
      img_puti(i,u,v,q);
      err += c - q;
    }
  }
}