static size_t EncodeImage(Image *image,const size_t bytes_per_line,
  const unsigned char *pixels,unsigned char *compressed_pixels)
{
  ssize_t
    y;

  register const unsigned char
    *p;

  register ssize_t
    i,
    x;

  register unsigned char
    *q;

  /*
    Runlength encode pixels.
  */
  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(pixels != (const unsigned char *) NULL);
  assert(compressed_pixels != (unsigned char *) NULL);
  p=pixels;
  q=compressed_pixels;
  i=0;
  for (y=0; y < (ssize_t) image->rows; y++)
  {
    for (x=0; x < (ssize_t) bytes_per_line; x+=i)
    {
      /*
        Determine runlength.
      */
      for (i=1; ((x+i) < (ssize_t) bytes_per_line); i++)
        if ((*(p+i) != *p) || (i == 255))
          break;
      *q++=(unsigned char) i;
      *q++=(*p);
      p+=i;
    }
    /*
      End of line.
    */
    *q++=0x00;
    *q++=0x00;
    if (SetImageProgress(image,LoadImageTag,y,image->rows) == MagickFalse)
      break;
  }
  /*
    End of bitmap.
  */
  *q++=0;
  *q++=0x01;
  return((size_t) (q-compressed_pixels));
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.