🚀 go-pugleaf

>  Could you please enquire on the network whether some body has a fast
>  algorithm for rotating by 90 degrees very very large monochrome or
>  multichannel images. The problem is nontrivial and probably can be
>  handled by exchanging in and out of a limited size buffer that can be
>  stored in high speed memory. I have an urgent need for this if we can
>  find one.

I got two useful replies.

1.  From eddins@eecs.uic, bamberg%trane.eecs.wsu.edu, and haim@utdallas.edu:
  
    Well, there might be something around that's newer and faster, but
    consider:
     
    J. O. Eklundh, "A Fast Computer Method for Matrix Transposing,"  IEEE
    Transactions on Computers, C-21 (July 1972), 801-903.
     
    This method is described in:
     
    D. E. Dudgeon and R. M. Mersereau, Multidimensional Digital Signal
    Processing, Prentice-Hall, New Jersey, 1984.
   
2.  From pfk@hpux.rz.uni-jena.de:

    I know a solution working in this way (C-Notation):
     
    #define MAXX    16384
    #define MAXY    16384
    #define MAXB      512  /* MAXB*MAXX*(Bytes_per_Pixel) should be smaller
                              than the main memory. I.e. This is an example
                              for 16 MB RAM and 8 bits per pixel. */
     
    static unsigned char buffer[MAXY][MAXB], buffero[MAXY];
    register i, j, k;
     
    for (i=0; i<MAXX; i+=MAXB)
      { for (j=0; j<MAXY; j++)
          lseek(fdin,j*MAXX+i,SEEK_SET),
          read(fdin,buffer[j],MAXB);
        for (j=0; j<MAXB; j++)
          { for (k=0; k<MAXY; k++)
              buffero[k]=buffer[k][j];
            write(fdout,buffero,MAXY);
          }
      }
     
-- 
cristy@dupont.com