source: libpipi/trunk/pipi/filter/blur.c @ 2715 Tweet

/*
 *  libpipi       Proper image processing implementation library
 *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
 *                All Rights Reserved
 *
 *  $Id$
 *
 *  This library is free software. It comes without any warranty, to
 *  the extent permitted by applicable law. You can redistribute it
 *  and/or modify it under the terms of the Do What The Fuck You Want
 *  To Public License, Version 2, as published by Sam Hocevar. See
 *  http://sam.zoy.org/wtfpl/COPYING for more details.
 */

/*
 * blur.c: blur functions
 */

#include "config.h"
#include "common.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

#include "pipi.h"
#include "pipi_internals.h"

/* Any standard deviation below this value will be rounded up, in order
 * to avoid ridiculously low values. exp(-1/(2*0.2*0.2)) is < 10^-5 so
 * there is little chance that any value below 0.2 will be useful. */
#define BLUR_EPSILON 0.2

pipi_image_t *pipi_gaussian_blur(pipi_image_t *src, float radius)
{
    return pipi_gaussian_blur_ext(src, radius, radius, 0.0, 0.0, 0.0);
}

pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
                                     float angle, float dx, float dy)
{
    pipi_image_t *ret;
    double *kernel;
    double Kx, Ky, t = 0.0, sint, cost, bbx, bby;
    int i, j, krx, kry, m, n;

    if(rx < BLUR_EPSILON) rx = BLUR_EPSILON;
    if(ry < BLUR_EPSILON) ry = BLUR_EPSILON;

    sint = sin(angle * M_PI / 180.);
    cost = cos(angle * M_PI / 180.);

    /* Compute the final ellipse's bounding box */
    bbx = sqrt(rx * rx * cost * cost + ry * ry * sint * sint);
    bby = sqrt(ry * ry * cost * cost + rx * rx * sint * sint);

    /* FIXME: the kernel becomes far too big with large values of dx, because
     * we grow both left and right. Fix the growing direction. */
    krx = (int)(3. * bbx + .99999 + ceil(abs(dx)));
    m = 2 * krx + 1;
    Kx = -1. / (2. * rx * rx);

    kry = (int)(3. * bby + .99999 + ceil(abs(dy)));
    n = 2 * kry + 1;
    Ky = -1. / (2. * ry * ry);

    kernel = malloc(m * n * sizeof(double));

    for(j = -kry; j <= kry; j++)
    {
        for(i = -krx; i <= krx; i++)
        {
            double u = (double)i * cost - (double)j * sint + dx;
            double v = (double)j * cost + (double)i * sint + dy;
            double ex = Kx * u * u;
            double ey = Ky * v * v;
            double d = exp(ex + ey);

            kernel[(j + kry) * m + i + krx] = d;
            t += d;
        }
    }

    for(j = 0; j < n; j++)
        for(i = 0; i < m; i++)
            kernel[j * m + i] /= t;

    ret = pipi_convolution(src, m, n, kernel);

    free(kernel);

    return ret;
}

/* FIXME: box blur would be incredibly faster using an accumulator instead
 * of a convolution filter... */
pipi_image_t *pipi_box_blur(pipi_image_t *src, int size)
{
    return pipi_box_blur_ext(src, size, size);
}

pipi_image_t *pipi_box_blur_ext(pipi_image_t *src, int m, int n)
{
    pipi_image_t *ret;
    double *kernel;
    int i;

    kernel = malloc(m * n * sizeof(double));
    for(i = 0; i < m * n; i++)
        kernel[i] = 1. / (m * n);

    ret = pipi_convolution(src, m, n, kernel);

    free(kernel);

    return ret;
}