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Posts Tagged ‘fringe projection’

Creating Gray-Code sequences using gimp

June 15th, 2009 admin No comments

I needed to implement gray-code sequences for a fringe projection system i'm trying to build. To avoid hard to understand and not really intuitive C-code, i used gimp to produce the projection images. In this article i'm going to document the code used.

First is the script-fu function to generate a picture with a given number of fringes or - alternatively - a given width of the period:

PLAIN TEXT
CODE:
  1. (define (script-fu-oan-create-fringes fwidth t fcount)
  2. (let*
  3.     (
  4.     (myimg (aref (cadr (gimp-image-list)) 0))
  5.     (mylayer (gimp-image-active-drawable myimg))
  6.     (layers (gimp-image-get-layers  myimg))
  7.     (channels (gimp-image-get-channels myimg))
  8.     (height (car (gimp-drawable-height (car mylayer))))
  9.     )
  10.     (if (= t TRUE) (set! fwidth (/ (car (gimp-drawable-width (car mylayer))) (* anzahl 2)))
  11.                     (set! fcount (/ (car (gimp-drawable-width (car mylayer))) (* breite 2)))
  12.     )
  13.     (define i 0)
  14.     (gimp-selection-all myimg)
  15.     (gimp-edit-clear (car mylayer))
  16.     (gimp-selection-none myimg)
  17.     (while
  18.         (<i fcount)
  19.         (gimp-rect-select myimg (* (* fwidth i) 2) 0 fwidth height CHANNEL-OP-ADD FALSE 0)
  20.         (set! i (+ i 1))
  21.     )
  22.     (gimp-edit-bucket-fill (car mylayer) FG-BUCKET-FILL NORMAL-MODE 100 0 FALSE 0 0)
  23. )
  24. )

Then there is the register-function call to enable the menu item for the function:

PLAIN TEXT
CODE:
  1. (script-fu-register
  2. "script-fu-oan-create-fringes"                              ;func name
  3. "Create Fringes"                                            ;menu label
  4. "Create an image of fringes\
  5.  "                                                          ;description
  6. "Omar Abo-Namous"                                           ;author
  7. "copyright 2009, Omar Abo-Namous"                           ;copyright notice
  8. "March 02, 2009"                                            ;date created
  9. ""                                                          ;image type that the script works on
  10. SF-VALUE "Fringe width:" "16"                               ;
  11. SF-TOGGLE "Use Fringe count" FALSE                  ;
  12. SF-VALUE "Fringe count:" "8"                            ;
  13. )
  14. (script-fu-menu-register "script-fu-oan-create-fringes" "<Image>/Xtns")

An older in-depth script-fu article by me.

Categories: Programming, Science Tags: , ,

Convert Gray-Code to decimal/binary and back

February 16th, 2009 admin No comments

Gray-Code is a binary code developed by Frank Gray in 1947. It is used by most absolute incremental encoders and some favor it's use for fringe projection systems that have to encode the pixel data in a series of image patterns (mostly fringes with differing widths). To convert Gray-Code from and to Decimal numbers using c++ i had to look up different approaches with varying difficulty levels. I then compiled the following algorithms, that i will be using for my own fringe projection system (keep tuned).

It's rather easy if you know how to do it. I had to find out the hard way, so here's for the rest of the world:

First the easy part: transforming a integer number dec into a Gray-code _code:

PLAIN TEXT
C++:
  1. void _calculateGrayCode () {
  2.     bitset<numeric_limits<int>::digits + 1> bs(dec);
  3.     bitset<numeric_limits<int>::digits + 1> gs(dec);
  4.     bitset<numeric_limits<int>::digits + 1> _code(0);
  5.     bs>>= 1;
  6.     gs ^= bs;
  7.     for (unsigned i=0; i<_code.size(); i++){
  8.         _code[i] = gs[i];
  9.         gs[i]=0;
  10.     }
  11. }

Now to the part of converting Gray-Code to binary and then decimal number: Suppose our Gray-code is inside the bitset _code.

PLAIN TEXT
C++:
  1. void _calculateNumber () {
  2.     bitset<numeric_limits<int>::digits + 1> gs(0);
  3.     bitset<numeric_limits<int>::digits + 1> bs(0);
  4.     for (unsigned i=0; i<_code.size(); i++){
  5.         gs[i] = _code[i];
  6.     }
  7.     bs[gs.size()-1] = gs[gs.size()-1];
  8.     for (int i=gs.size()-2; i>=0;i--){
  9.         bs[i]=bs[i+1];
  10.         bs[i]=bs[i]^gs[i];
  11.     }
  12.     _number = static_cast<int>(bs.to_ulong());
  13. }

bs holds the binary representation of the Gray-Code and _number is the decimal respresentation.

References:

Categories: Programming, Science Tags: , , , ,