srecord noeq Hi15ImageStreaks(Hi15Image inputImage) {
  // pixel indices of streak ends
  new IntBuffer streakData;
  int[] lineStarts;
  gettable int w;
  
  run {
    var streakData = this.streakData;
    int w = this.w = inputImage.w(), h = inputImage.h();
    lineStarts = new int[h+1];
    short[] pixels = inputImage.pixels;
    int iPixel = 0;
    
    for y to h: {
      lineStarts[y] = streakData.size();
      int lineEnd = iPixel+w;
      while (iPixel < lineEnd) {
        short color = pixels[iPixel];
        do
          ++iPixel;
        while (iPixel < lineEnd && pixels[iPixel] == color);
        streakData.add(iPixel);
      }
    }
    
    lineStarts[l(lineStarts)-1] = streakData.size();
  }
  
  selfType runAndReturn() { run(); this; }
  
  int nStreaks() { ret streakData.size(); }
  int h() { ret lineStarts.length-1; }
  
  int lineEnd(int y) { ret lineStarts[y+1]; }
  
  L<Rect> streaksAsRects() {
    ret listFromFunction(nStreaks(), iStreak -> {
      int iPixel = iStreak == 0 ? 0 : streakData.get(iStreak-1);
      int jPixel = streakData.get(iStreak++);
      int w = w();
      ret rect(iPixel % w, iPixel/w, jPixel-iPixel, 1);
    });
  }
}