/*****************************************************************************
*                                                                            *
*   HISTEQ.SPL   Copyright (C) 1998-2000 DSP Development Corporation         *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Performs histogram equalization of an image                 *
*                                                                            *
*   Revisions:   16 Mar 1998  RRR  Creation                                  *
*                 3 May 2000  RRR  rgb2mono conversion                       *
*                                                                            *
*****************************************************************************/

#include 

#if @HELP_HISTEQ

    HISTEQ

    Purpose: Performs histogram equalization of an image

    Syntax:  HISTEQ(array, intflag)

              array   - input image

              intflag - an optional integer, cast result to
                        integer values (default 0)

    Returns: An array

    Example:
             W1: Density(Ravel(gsin(400, 1/400, 4), 20))
             W2: Histeq(W1)

             returns an equalized image

    Remarks:
             Histeq expects an image of integer values. If the input
             image is 24 bit (RGB values), the image is automatically
             converted to 8 bit monochrome.


    See Also:
             Ampdist
             Histogram
             Image24
             Partsum
             Rgb2mono

#endif


/* histogram equalization - for integer images */
histeq(a, intflag)
{
        local n, m, ua, heq;

        if (argc < 2)
        {
                if (argc < 1) error("histeq - input array required");
                
                intflag = FALSE;
        }

        (n, m) = size(a);

        if (n < 2 || m < 2) error("histeq - input array required");

        if (rgbimage(a))
        {
                printf("histeq - converting 24 bit image to 8 bit ...");
                a = rgb2mono(a);
        }

        printf("histeq - equalizing ...");

        ua = a[..];

        /* get image max and min */
        umin = min(ua);
        umax = max(ua);

        /* produce normalized histogram lookup table */
        htable = umax * partsum(ampdist(ua, 1)) / length(ua);

        /* lookup new values - indices start at 1 */
        heq = htable[ua-umin+1];

        /* scale to original image */
        heq = histeq_normeq(heq, umin, umax);

        if (intflag) heq = int(heq);

        /* shape */
        heq = ravel(heq, n);

        /* set deltax and deltay */
        setdeltax(heq, deltax(a));
        setdeltay(heq, deltay(a));

        /* convert to density plot */
        setplottype(heq, 3);
        setplotstyle(heq, 0);

        return(heq);
}


/* normalize a series from newmin to newmax */
histeq_normeq(a, newmin, newmax)
{
        return(((a - min(a)) / (max(a) - min(a))) * (newmax - newmin) + newmin);
}