Pillow

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/*
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 * The Python Imaging Library
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 * $Id$
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 *
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 * mode filter
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 *
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 * history:
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 * 2002-06-08 fl    Created (based on code from IFUNC95)
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 * 2004-10-05 fl    Rewritten; use a simpler brute-force algorithm
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 *
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 * Copyright (c) Secret Labs AB 2002-2004.  All rights reserved.
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 *
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 * See the README file for information on usage and redistribution.
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 */
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#include "Imaging.h"
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Imaging
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ImagingModeFilter(Imaging im, int size) {
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    Imaging imOut;
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    int x, y, i;
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    int xx, yy;
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    int maxcount;
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    UINT8 maxpixel;
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    int histogram[256];
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    if (!im || im->bands != 1 || im->type != IMAGING_TYPE_UINT8) {
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        return (Imaging)ImagingError_ModeError();
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    }
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    imOut = ImagingNewDirty(im->mode, im->xsize, im->ysize);
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    if (!imOut) {
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        return NULL;
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    }
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    size = size / 2;
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    for (y = 0; y < imOut->ysize; y++) {
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        UINT8 *out = &IMAGING_PIXEL_L(imOut, 0, y);
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        for (x = 0; x < imOut->xsize; x++) {
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            /* calculate histogram over current area */
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            /* FIXME: brute force! to improve, update the histogram
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               incrementally.  may also add a "frequent list", like in
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               the old implementation, but I'm not sure that's worth
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               the added complexity... */
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            memset(histogram, 0, sizeof(histogram));
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            for (yy = y - size; yy <= y + size; yy++) {
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                if (yy >= 0 && yy < imOut->ysize) {
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                    UINT8 *in = &IMAGING_PIXEL_L(im, 0, yy);
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                    for (xx = x - size; xx <= x + size; xx++) {
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                        if (xx >= 0 && xx < imOut->xsize) {
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                            histogram[in[xx]]++;
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                        }
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                    }
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                }
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            }
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            /* find most frequent pixel value in this region */
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            maxpixel = 0;
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            maxcount = histogram[maxpixel];
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            for (i = 1; i < 256; i++) {
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                if (histogram[i] > maxcount) {
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                    maxcount = histogram[i];
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                    maxpixel = (UINT8)i;
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                }
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            }
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            if (maxcount > 2) {
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                out[x] = maxpixel;
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            } else {
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                out[x] = IMAGING_PIXEL_L(im, x, y);
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            }
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        }
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    }
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    ImagingCopyPalette(imOut, im);
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    return imOut;
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}
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