/*!
* pixOtsuAdaptiveThreshold()
*
* Input: pixs (8 bpp)
* sx, sy (desired tile dimensions; actual size may vary)
* smoothx, smoothy (half-width of convolution kernel applied to
* threshold array: use 0 for no smoothing)
* scorefract (fraction of the max Otsu score; typ. 0.1;
* use 0.0 for standard Otsu)
* &pixth (<optional return> array of threshold values
* found for each tile)
* &pixd (<optional return> thresholded input pixs, based on
* the threshold array)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) The Otsu method finds a single global threshold for an image.
* This function allows a locally adapted threshold to be
* found for each tile into which the image is broken up.
* (2) The array of threshold values, one for each tile, constitutes
* a highly downscaled image. This array is optionally
* smoothed using a convolution. The full width and height of the
* convolution kernel are (2 * @smoothx + 1) and (2 * @smoothy + 1).
* (3) The minimum tile dimension allowed is 16. If such small
* tiles are used, it is recommended to use smoothing, because
* without smoothing, each small tile determines the splitting
* threshold independently. A tile that is entirely in the
* image bg will then hallucinate fg, resulting in a very noisy
* binarization. The smoothing should be large enough that no
* tile is only influenced by one type (fg or bg) of pixels,
* because it will force a split of its pixels.
* (4) To get a single global threshold for the entire image, use
* input values of @sx and @sy that are larger than the image.
* For this situation, the smoothing parameters are ignored.
* (5) The threshold values partition the image pixels into two classes:
* one whose values are less than the threshold and another
* whose values are greater than or equal to the threshold.
* This is the same use of 'threshold' as in pixThresholdToBinary().
* (6) The scorefract is the fraction of the maximum Otsu score, which
* is used to determine the range over which the histogram minimum
* is searched. See numaSplitDistribution() for details on the
* underlying method of choosing a threshold.
* (7) This uses enables a modified version of the Otsu criterion for
* splitting the distribution of pixels in each tile into a
* fg and bg part. The modification consists of searching for
* a minimum in the histogram over a range of pixel values where
* the Otsu score is within a defined fraction, @scorefract,
* of the max score. To get the original Otsu algorithm, set
* @scorefract == 0.
*/
l_int32
pixOtsuAdaptiveThreshold(PIX *pixs,
l_int32 sx,
l_int32 sy,
l_int32 smoothx,
l_int32 smoothy,
l_float32 scorefract,
PIX **ppixth,
PIX **ppixd)
{
l_int32 w, h, nx, ny, i, j, thresh;
l_uint32 val;
PIX *pixt, *pixb, *pixthresh, *pixth, *pixd;
PIXTILING *pt;
PROCNAME("pixOtsuAdaptiveThreshold");
if (!ppixth && !ppixd){
return ERROR_INT("neither &pixth nor &pixd defined", procName, 1);
LOGE("neither &pixth nor &pixd defined");
}
if (ppixth) *ppixth = NULL;
if (ppixd) *ppixd = NULL;
if (!pixs || pixGetDepth(pixs) != 8){
return ERROR_INT("pixs not defined or not 8 bpp", procName, 1);
LOGE("pixs not defined or not 8 bpp");
}
if (sx < 16 || sy < 16){
return ERROR_INT("sx and sy must be >= 16", procName, 1);
LOGE("sx and sy must be >= 16");
}
/* Compute the threshold array for the tiles */
pixGetDimensions(pixs, &w, &h, NULL);
nx = L_MAX(1, w / sx);
ny = L_MAX(1, h / sy);
smoothx = L_MIN(smoothx, (nx - 1) / 2);
smoothy = L_MIN(smoothy, (ny - 1) / 2);
pt = pixTilingCreate(pixs, nx, ny, 0, 0, 0, 0);
pixthresh = pixCreate(nx, ny, 8);
for (i = 0; i < ny; i++) {
for (j = 0; j < nx; j++) {
pixt = pixTilingGetTile(pt, i, j);
pixSplitDistributionFgBg(pixt, scorefract, 1, &thresh,
NULL, NULL, 0);
pixSetPixel(pixthresh, j, i, thresh); /* see note (4) */
pixDestroy(&pixt);
}
}
/* Optionally smooth the threshold array */
if (smoothx > 0 || smoothy > 0)
pixth = pixBlockconv(pixthresh, smoothx, smoothy);
else
pixth = pixClone(pixthresh);
pixDestroy(&pixthresh);
/* Optionally apply the threshold array to binarize pixs */
if (ppixd) {
pixd = pixCreate(w, h, 1);
for (i = 0; i < ny; i++) {
for (j = 0; j < nx; j++) {
pixt = pixTilingGetTile(pt, i, j);
pixGetPixel(pixth, j, i, &val);
pixb = pixThresholdToBinary(pixt, val);
pixTilingPaintTile(pixd, i, j, pixb, pt);
pixDestroy(&pixt);
pixDestroy(&pixb);
}
}
*ppixd = pixd;
}
if (ppixth)
*ppixth = pixth;
else
pixDestroy(&pixth);
pixTilingDestroy(&pt);
return 0;
}
int main(int argc,
char **argv) {
char textstr[256];
l_int32 i, thresh, fgval, bgval;
l_float32 scorefract;
L_BMF *bmf;
PIX *pixs, *pixb, *pixb2, *pixb3, *pixg, *pixp, *pixt1, *pixt2;
PIXA *pixa;
pixs = pixRead("1555-7.jpg");
pixg = pixConvertTo8(pixs, 0);
bmf = bmfCreate("fonts", 8);
for (i = 0; i < 3; i++) {
pixa = pixaCreate(3);
scorefract = 0.1 * i;
pixOtsuAdaptiveThreshold(pixg, 2000, 2000, 0, 0, scorefract,
NULL, &pixb);
pixSaveTiledOutline(pixb, pixa, 0.5, 1, 20, 2, 32);
pixSplitDistributionFgBg(pixg, scorefract, 1, &thresh, &fgval, &bgval, 1);
fprintf(stderr, "thresh = %d, fgval = %d, bgval = %d\n", thresh, fgval,
bgval);
/* Give gnuplot time to write out the plot */
#ifndef _WIN32
sleep(1);
#else
Sleep(1000);
#endif /* _WIN32 */
pixp = pixRead("/tmp/histplot.png");
pixSaveTiled(pixp, pixa, 1.0, 0, 20, 1);
pixt1 = pixaDisplay(pixa, 0, 0);
snprintf(textstr, sizeof(textstr),
"Scorefract = %3.1f ........... Thresh = %d", scorefract, thresh);
pixt2 = pixAddSingleTextblock(pixt1, bmf, textstr, 0x00ff0000,
L_ADD_BELOW, NULL);
pixDisplay(pixt2, 100, 100);
snprintf(textstr, sizeof(textstr), "/tmp/otsu.%d.png", i);
pixWrite(textstr, pixt2, IFF_PNG);
pixDestroy(&pixb);
pixDestroy(&pixp);
pixDestroy(&pixt1);
pixDestroy(&pixt2);
pixaDestroy(&pixa);
}
pixa = pixaCreate(2);
for (i = 0; i < 2; i++) {
scorefract = 0.1 * i;
pixOtsuAdaptiveThreshold(pixg, 300, 300, 0, 0, scorefract,
NULL, &pixb);
pixb2 = pixAddBlackOrWhiteBorder(pixb, 2, 2, 2, 2, L_GET_BLACK_VAL);
snprintf(textstr, sizeof(textstr),
"Scorefract = %3.1f", scorefract);
pixb3 = pixAddSingleTextblock(pixb2, bmf, textstr, 1,
L_ADD_BELOW, NULL);
pixSaveTiled(pixb3, pixa, 2, (i + 1) % 1, 20, 32);
pixDestroy(&pixb);
pixDestroy(&pixb2);
}
pixb = pixaDisplay(pixa, 0, 0);
pixWrite("/tmp/otsu-tiled.jpg", pixb, IFF_PNG);
pixDestroy(&pixb);
pixaDestroy(&pixa);
bmfDestroy(&bmf);
pixDestroy(&pixs);
pixDestroy(&pixg);
return 0;
}