static size_t PSDPackbitsEncodeImage(Image *image,const size_t length,
  const unsigned char *pixels,unsigned char *compact_pixels,
  ExceptionInfo *exception)
{
  int
    count;

  register ssize_t
    i,
    j;

  register unsigned char
    *q;

  unsigned char
    *packbits;

  /*
    Compress pixels with Packbits encoding.
  */
  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  if (image->debug != MagickFalse)
    (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image->filename);
  assert(pixels != (unsigned char *) NULL);
  assert(compact_pixels != (unsigned char *) NULL);
  packbits=(unsigned char *) AcquireQuantumMemory(128UL,sizeof(*packbits));
  if (packbits == (unsigned char *) NULL)
    ThrowBinaryException(ResourceLimitError,"MemoryAllocationFailed",
      image->filename);
  q=compact_pixels;
  for (i=(ssize_t) length; i != 0; )
  {
    switch (i)
    {
      case 1:
      {
        i--;
        *q++=(unsigned char) 0;
        *q++=(*pixels);
        break;
      }
      case 2:
      {
        i-=2;
        *q++=(unsigned char) 1;
        *q++=(*pixels);
        *q++=pixels[1];
        break;
      }
      case 3:
      {
        i-=3;
        if ((*pixels == *(pixels+1)) && (*(pixels+1) == *(pixels+2)))
          {
            *q++=(unsigned char) ((256-3)+1);
            *q++=(*pixels);
            break;
          }
        *q++=(unsigned char) 2;
        *q++=(*pixels);
        *q++=pixels[1];
        *q++=pixels[2];
        break;
      }
      default:
      {
        if ((*pixels == *(pixels+1)) && (*(pixels+1) == *(pixels+2)))
          {
            /*
              Packed run.
            */
            count=3;
            while (((ssize_t) count < i) && (*pixels == *(pixels+count)))
            {
              count++;
              if (count >= 127)
                break;
            }
            i-=count;
            *q++=(unsigned char) ((256-count)+1);
            *q++=(*pixels);
            pixels+=count;
            break;
          }
        /*
          Literal run.
        */
        count=0;
        while ((*(pixels+count) != *(pixels+count+1)) ||
               (*(pixels+count+1) != *(pixels+count+2)))
        {
          packbits[count+1]=pixels[count];
          count++;
          if (((ssize_t) count >= (i-3)) || (count >= 127))
            break;
        }
        i-=count;
        *packbits=(unsigned char) (count-1);
        for (j=0; j <= (ssize_t) count; j++)
          *q++=packbits[j];
        pixels+=count;
        break;
      }
    }
  }
  *q++=(unsigned char) 128;  /* EOD marker */
  packbits=(unsigned char *) RelinquishMagickMemory(packbits);
  return((size_t) (q-compact_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.