img_sobel.h

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/*  TEXAS INSTRUMENTS, INC.                                                 */
/*                                                                          */
/*  IMGLIB  DSP Image/Video Processing Library                              */
/*                                                                          */
/*      Release:        Revision 1.04b                                      */
/*      CVS Revision:   1.6     Fri Oct 10 16:01:13 2003 (UTC)              */
/*      Snapshot date:  23-Oct-2003                                         */
/*                                                                          */
/*  This library contains proprietary intellectual property of Texas        */
/*  Instruments, Inc.  The library and its source code are protected by     */
/*  various copyrights, and portions may also be protected by patents or    */
/*  other legal protections.                                                */
/*                                                                          */
/*  This software is licensed for use with Texas Instruments TMS320         */
/*  family DSPs.  This license was provided to you prior to installing      */
/*  the software.  You may review this license by consulting the file       */
/*  TI_license.PDF which accompanies the files in this library.             */
/* ------------------------------------------------------------------------ */
/*          Copyright (C) 2003 Texas Instruments, Incorporated.             */
/*                          All Rights Reserved.                            */
/* ======================================================================== */
/* ======================================================================== */
/*  Assembler compatibility shim for assembling 4.30 and later code on      */
/*  tools prior to 4.30.                                                    */
/* ======================================================================== */
/* ======================================================================== */
/*  End of assembler compatibility shim.                                    */
/* ======================================================================== */
/* ======================================================================== */
/*  TEXAS INSTRUMENTS, INC.                                                 */
/*                                                                          */
/*  NAME                                                                    */
/*      IMG_sobel, Little Endian.                                           */
/*                                                                          */
/*  REVISION DATE                                                           */
/*      10-Oct-2003                                                         */
/*                                                                          */
/*  USAGE                                                                   */
/*      This routine is C-callable and can be called as:                    */
/*                                                                          */
/*      void IMG_sobel                                                      */
/*      (                                                                   */
/*          const unsigned char *in_data,      // Input image data  //      */
/*          unsigned char       *out_data,     // Output image data //      */
/*          short cols, short rows             // Image dimensions  //      */
/*      )                                                                   */
/*                                                                          */
/*      The IMG_sobel filter is applied to the input image. The input image */
/*      dimensions are given by the arguments 'cols' and 'rows'.  The       */
/*      output image is 'cols' pixels wide and 'rows - 2' pixels tall.      */
/*                                                                          */
/*  DESCRIPTION                                                             */
/*                                                                          */
/*      To see how the implementation is going to work on the input         */
/*      buffer, lets imagine we have the following input buffer:            */
/*                                                                          */
/*              yyyyyyyyyyyyyyyy                                            */
/*              yxxxxxxxxxxxxxxy                                            */
/*              yxxxxxxxxxxxxxxy                                            */
/*              yxxxxxxxxxxxxxxy                                            */
/*              yxxxxxxxxxxxxxxy                                            */
/*              yyyyyyyyyyyyyyyy                                            */
/*                                                                          */
/*      The output buffer would be:                                         */
/*                                                                          */
/*              tXXXXXXXXXXXXXXz                                            */
/*              zXXXXXXXXXXXXXXz                                            */
/*              zXXXXXXXXXXXXXXz                                            */
/*              zXXXXXXXXXXXXXXt                                            */
/*                                                                          */
/*      Where:                                                              */
/*                                                                          */
/*          X = IMG_sobel(x)    The algorithm is applied to that pixel.     */
/*                          The correct output is obtained, the data        */
/*                          around the pixels we work on is used            */
/*                                                                          */
/*          t               Whatever was in the output buffer in that       */
/*                          position is kept there.                         */
/*                                                                          */
/*          z = IMG_sobel(y)    The algorithm is applied to that pixel.     */
/*                          The output is not meaningful, because the       */
/*                          necessary data to process the pixel is not      */
/*                          available.  This is because for each output     */
/*                          pixel we need input pixels from the right and   */
/*                          from the left of the output pixel.  But this    */
/*                          data doesn't exist.                             */
/*                                                                          */
/*      This means that we will only process (rows-2) lines.  Then, we      */
/*      will process all the pixels inside each line. Even though the       */
/*      results for the first and last pixels in each line will not         */
/*      be relevant, it makes the control much simpler and ends up          */
/*      saving cycles.                                                      */
/*                                                                          */
/*      Also the first pixel in the first processed line and the            */
/*      last pixel in the last processed line will not be computed.         */
/*      It is not necessary, since the results would be bogus.              */
/*                                                                          */
/*      The following horizontal and vertical masks that are                */
/*      applied to the input buffer to obtain one output pixel.             */
/*                                                                          */
/*          Horizontal:                                                     */
/*              -1 -2 -1                                                    */
/*               0  0  0                                                    */
/*               1  2  1                                                    */
/*                                                                          */
/*          Vertical:                                                       */
/*              -1  0  1                                                    */
/*              -2  0  2                                                    */
/*              -1  0  1                                                    */
/*                                                                          */
/*      This is a C model of the Sobel implementation.  This C code         */
/*      is functionally equivalent to the assembly code without             */
/*      restrictions.   The assembly code may impose additional             */
/*      restrictions.                                                       */
/*                                                                          */
/*          void IMG_sobel                                                  */
/*          (                                                               */
/*              const unsigned char *in,       // Input image data  //      */
/*              unsigned char       *out,      // Output image data //      */