Martin, Thanks for all your help. I have a final question about the sprintf solution. I have managed to get the out going(I think) but I am not quite undestanding the atol()inlet part. I have this.

void window_getframe(t_window *x, t_symbol *sym) { char* decode; char symstr; x->sym->s_name = decode; symstr = atol(decode); frame = symstr; } But I get invalid conversion from 'char' to "IplImage*'. I have to read some more. If I used sprintf to write
to an array a string/image formatted as a pointer and then turned that pointer to a symbol, how do i now convert the symbol back to a pointer of the original image, which I assume should still be in buffer? Alain

You can only work with atoms in pd's message system, and each atom usually contains a bang, a

float or a symbol. You could convert the pointer to a float but it probably won't work because the pointer is a large integer that won't be accurately represented as a float. You could convert the pointer to a symbol using something like:

char symstr[10]; t_symbol sym; sprintf(symstr, "%p", frame); sym = gensym(symstr); ...then send sym through the outlet and convert it back to a pointer at the receiving end by extracting

the string from the s_name field of the symbol and passing it to atol().

Martin