Exemple #1
0
/*!
 *  pixMaskedThreshOnBackgroundNorm()
 *
 *      Input:  pixs (8 bpp grayscale; not colormapped)
 *              pixim (<optional> 1 bpp 'image' mask; can be null)
 *              sx, sy (tile size in pixels)
 *              thresh (threshold for determining foreground)
 *              mincount (min threshold on counts in a tile)
 *              smoothx (half-width of block convolution kernel width)
 *              smoothy (half-width of block convolution kernel height)
 *              scorefract (fraction of the max Otsu score; typ. ~ 0.1)
 *              &thresh (<optional return> threshold value that was
 *                       used on the normalized image)
 *      Return: pixd (1 bpp thresholded image), or null on error
 *
 *  Notes:
 *      (1) This begins with a standard background normalization.
 *          Additionally, there is a flexible background norm, that
 *          will adapt to a rapidly varying background, and this
 *          puts white pixels in the background near regions with
 *          significant foreground.  The white pixels are turned into
 *          a 1 bpp selection mask by binarization followed by dilation.
 *          Otsu thresholding is performed on the input image to get an
 *          estimate of the threshold in the non-mask regions.
 *          The background normalized image is thresholded with two
 *          different values, and the result is combined using
 *          the selection mask.
 *      (2) Note that the numbers 255 (for bgval target) and 190 (for
 *          thresholding on pixn) are tied together, and explicitly
 *          defined in this function.
 *      (3) See pixBackgroundNorm() for meaning and typical values
 *          of input parameters.  For a start, you can try:
 *            sx, sy = 10, 15
 *            thresh = 100
 *            mincount = 50
 *            smoothx, smoothy = 2
 */
PIX *
pixMaskedThreshOnBackgroundNorm(PIX       *pixs,
                                PIX       *pixim,
                                l_int32    sx,
                                l_int32    sy,
                                l_int32    thresh,
                                l_int32    mincount,
                                l_int32    smoothx,
                                l_int32    smoothy,
                                l_float32  scorefract,
                                l_int32   *pthresh)
{
l_int32   w, h;
l_uint32  val;
PIX      *pixn, *pixm, *pixd, *pixt1, *pixt2, *pixt3, *pixt4;

    PROCNAME("pixMaskedThreshOnBackgroundNorm");

    if (pthresh) *pthresh = 0;
    if (!pixs || pixGetDepth(pixs) != 8)
        return (PIX *)ERROR_PTR("pixs undefined or not 8 bpp", procName, NULL);
    if (pixGetColormap(pixs))
        return (PIX *)ERROR_PTR("pixs is colormapped", procName, NULL);
    if (sx < 4 || sy < 4)
        return (PIX *)ERROR_PTR("sx and sy must be >= 4", procName, NULL);
    if (mincount > sx * sy) {
        L_WARNING("mincount too large for tile size\n", procName);
        mincount = (sx * sy) / 3;
    }

        /* Standard background normalization */
    pixn = pixBackgroundNorm(pixs, pixim, NULL, sx, sy, thresh,
                             mincount, 255, smoothx, smoothy);
    if (!pixn)
        return (PIX *)ERROR_PTR("pixn not made", procName, NULL);

        /* Special background normalization for adaptation to quickly
         * varying background.  Threshold on the very light parts,
         * which tend to be near significant edges, and dilate to
         * form a mask over regions that are typically text.  The
         * dilation size is chosen to cover the text completely,
         * except for very thick fonts. */
    pixt1 = pixBackgroundNormFlex(pixs, 7, 7, 1, 1, 20);
    pixt2 = pixThresholdToBinary(pixt1, 240);
    pixInvert(pixt2, pixt2);
    pixm = pixMorphSequence(pixt2, "d21.21", 0);
    pixDestroy(&pixt1);
    pixDestroy(&pixt2);

        /* Use Otsu to get a global threshold estimate for the image,
         * which is stored as a single pixel in pixt3. */
    pixGetDimensions(pixs, &w, &h, NULL);
    pixOtsuAdaptiveThreshold(pixs, w, h, 0, 0, scorefract, &pixt3, NULL);
    if (pixt3 && pthresh) {
        pixGetPixel(pixt3, 0, 0, &val);
        *pthresh = val;
    }
    pixDestroy(&pixt3);

        /* Threshold the background normalized images differentially,
         * using a high value correlated with the background normalization
         * for the part of the image under the mask (i.e., near the
         * darker, thicker foreground), and a value that depends on the Otsu
         * threshold for the rest of the image.  This gives a solid
         * (high) thresholding for the foreground parts of the image,
         * while allowing the background and light foreground to be
         * reasonably well cleaned using a threshold adapted to the
         * input image. */
    pixd = pixThresholdToBinary(pixn, val + 30);  /* for bg and light fg */
    pixt4 = pixThresholdToBinary(pixn, 190);  /* for heavier fg */
    pixCombineMasked(pixd, pixt4, pixm);
    pixDestroy(&pixt4);
    pixDestroy(&pixm);
    pixDestroy(&pixn);

    if (!pixd)
        return (PIX *)ERROR_PTR("pixd not made", procName, NULL);
    else
        return pixd;
}
Exemple #2
0
Pix* norm(Pix* pix) {
    return pixBackgroundNormFlex(pix, 6, 6, 2, 2, 25);
}