I am trying to parallellize bitmap operations. This appears to be well 
possible for scanlines. Typical code reads like this:


// inside a tthread derived class do the following in execute
// where index points at the scanline to be prcoessed


s := source_bitmap.Scanline [index];
t := target_bitmap.Scanline [index];
for x := 0 to source_bitmap.Width - 1 do
begin
    pixel := s [x];
    // do something with pixel
    t [x] := pixel;
end;


It appears to be threadsafe, each thread processing his own index. I 
have tested this code very often. However, very rarely I get a illegal 
memory read/write. Are there things I overlook? Should I read some 
articles (i couldn't find them)?


Greetings,


Arnold