/**************************************************************************
 * Func: e_i_contrast                                                     *
 *                                                                        *
 * Desc: perform ends-in contrast stretch on image                        *
 *                                                                        *
 * Params: source - pointer to the source image                           *
 *         cols - number of columns in image                              *
 *         rows - number of rows in image                                 *
 *         low - percentage of pixels to set to 0                         *
 *         high - percentage of pixels to set to 255                      *
 **************************************************************************/

void e_i_contrast( image_ptr source, int cols, int rows,
		  float low, float high)
    {
    long i;                    /* loop variable */
    long number_of_pixels;     /* total number of pixels in image */
    long hist[256];            /* image histogram */
    unsigned char LUT[256];    /* Look-up table for final transformation */
    int lowthresh, highthresh; /* lower and upper thresholds */
    long runsum;               /* sum used to compute thresholds */
    float scale_factor;        /* scaling factor to compute new LUT values */

    /* calculate histogram */
    number_of_pixels = (long) cols * rows;
    for(i=0; i<256; i++)
	hist[i]=0;

    for(i=0; i<number_of_pixels; i++)
	hist[source[i]]++;

    printf(" low = %f    high = %f\n",low,high);

    runsum=0;
    lowthresh=0;
    for(i=0; i<256; i++)
	{
	runsum += hist[i];
	if((runsum*100.0/number_of_pixels) >= low)
	    {
	    lowthresh=i;
	    break;
	    }
	 }

    runsum=0;
    highthresh=255;
    for(i=255; i>=0; i--)
	{
	runsum += hist[i];
	if((runsum*100.0/number_of_pixels) >= high)
	    {
	    highthresh=i;
	    break;
	    }
	}

    printf("Low threshold is %d High threshold is %d\n",lowthresh,highthresh);

    for(i=0; i<lowthresh; i++)
	LUT[i]=0;

    for(i=255; i>highthresh; i--)
	LUT[i]=255;

    scale_factor = 255.0 / (highthresh - lowthresh);
    for(i=lowthresh; i<=highthresh; i++)
      LUT[i]=(i - lowthresh) * scale_factor;

    /* transfer new image */

    for(i=0; i<number_of_pixels; i++)
	source[i] = LUT[source[i]];

    }