@@ -32,6 +32,9 @@ BinaryImage binarizeSauvola(const QImage& src, const QSize windowSize, const dou
3232 }
3333
3434 const QImage gray (toGrayscale (src));
35+ if (gray.isNull ()) {
36+ return BinaryImage ();
37+ }
3538 const int w = gray.width ();
3639 const int h = gray.height ();
3740
@@ -114,6 +117,9 @@ BinaryImage binarizeWolf(const QImage& src,
114117 }
115118
116119 const QImage gray (toGrayscale (src));
120+ if (gray.isNull ()) {
121+ return BinaryImage ();
122+ }
117123 const int w = gray.width ();
118124 const int h = gray.height ();
119125
@@ -211,6 +217,9 @@ BinaryImage binarizeBradley(const QImage& src, const QSize windowSize, const dou
211217 }
212218
213219 QImage gray (toGrayscale (src));
220+ if (gray.isNull ()) {
221+ return BinaryImage ();
222+ }
214223 const int w = gray.width ();
215224 const int h = gray.height ();
216225
@@ -268,6 +277,120 @@ BinaryImage binarizeBradley(const QImage& src, const QSize windowSize, const dou
268277 return bwImg;
269278} // binarizeBradley
270279
280+ BinaryImage binarizeGrad (const QImage& src, const QSize windowSize, const double k, const double delta) {
281+ if (windowSize.isEmpty ()) {
282+ throw std::invalid_argument (" binarizeGrad: invalid windowSize"
283+ }
284+
285+ if (src.isNull ()) {
286+ return BinaryImage ();
287+ }
288+
289+ QImage gray (toGrayscale (src));
290+ if (gray.isNull ()) {
291+ return BinaryImage ();
292+ }
293+ QImage gmean (toGrayscale (src));
294+ if (gmean.isNull ()) {
295+ return BinaryImage ();
296+ }
297+ const int w = gray.width ();
298+ const int h = gray.height ();
299+
300+ const uint8_t * grayLine = gray.bits ();
301+ const int grayBpl = gray.bytesPerLine ();
302+
303+ uint8_t * gmeanLine = gmean.bits ();
304+ const int gmeanBpl = gmean.bytesPerLine ();
305+
306+ IntegralImage<uint32_t > integralImage (w, h);
307+
308+ for (int y = 0 ; y < h; ++y) {
309+ integralImage.beginRow ();
310+ for (int x = 0 ; x < w; ++x) {
311+ const uint32_t pixel = grayLine[x];
312+ integralImage.push (pixel);
313+ }
314+ grayLine += grayBpl;
315+ }
316+
317+ const int windowLowerHalf = windowSize.height () >> 1 ;
318+ const int windowUpperHalf = windowSize.height () - windowLowerHalf;
319+ const int windowLeftHalf = windowSize.width () >> 1 ;
320+ const int windowRightHalf = windowSize.width () - windowLeftHalf;
321+
322+ for (int y = 0 ; y < h; ++y) {
323+ const int top = std::max (0 , y - windowLowerHalf);
324+ const int bottom = std::min (h, y + windowUpperHalf); // exclusive
325+ for (int x = 0 ; x < w; ++x) {
326+ const int left = std::max (0 , x - windowLeftHalf);
327+ const int right = std::min (w, x + windowRightHalf); // exclusive
328+ const int area = (bottom - top) * (right - left);
329+ assert (area > 0 ); // because windowSize > 0 and w > 0 and h > 0
330+ const QRect rect (left, top, right - left, bottom - top);
331+ const double windowSum = integralImage.sum (rect);
332+
333+ const double rArea = 1.0 / area;
334+ const double mean = windowSum * rArea + 0.5 ;
335+ const int imean = (int )((mean < 0.0 ) ? 0.0 : (mean < 255.0 ) ? mean : 255.0 );
336+ gmeanLine[x] = imean;
337+ }
338+ gmeanLine += gmeanBpl;
339+ }
340+
341+ double gvalue = 127.5 ;
342+ double sum_g = 0.0 , sum_gi = 0.0 ;
343+ grayLine = gray.bits ();
344+ gmeanLine = gmean.bits ();
345+ for (int y = 0 ; y < h; y++){
346+ double sum_gl = 0.0 ;
347+ double sum_gil = 0.0 ;
348+ for (int x = 0 ; x < w; x++){
349+ double gi = grayLine[x];
350+ double g = gmeanLine[x];
351+ g -= gi;
352+ g = (g < 0.0 ) ? -g : g;
353+ gi *= g;
354+ sum_gl += g;
355+ sum_gil += gi;
356+ }
357+ sum_g += sum_gl;
358+ sum_gi += sum_gil;
359+ grayLine += grayBpl;
360+ gmeanLine += gmeanBpl;
361+ }
362+ gvalue = (sum_g > 0.0 ) ? (sum_gi / sum_g) : gvalue;
363+
364+ double const meanGrad = gvalue * (1.0 - k);
365+
366+ BinaryImage bwImg (w, h);
367+ uint32_t * bwLine = bwImg.data ();
368+ const int bwWpl = bwImg.wordsPerLine ();
369+
370+ grayLine = gray.bits ();
371+ gmeanLine = gmean.bits ();
372+ for (int y = 0 ; y < h; ++y) {
373+ for (int x = 0 ; x < w; ++x) {
374+ const double origin = grayLine[x];
375+ const double mean = gmeanLine[x];
376+ const double threshold = meanGrad + mean * k;
377+ const uint32_t msb = uint32_t (1 ) << 31 ;
378+ const uint32_t mask = msb >> (x & 31 );
379+ if (origin < (threshold + delta)) {
380+ // black
381+ bwLine[x >> 5 ] |= mask;
382+ } else {
383+ // white
384+ bwLine[x >> 5 ] &= ~mask;
385+ }
386+ }
387+ grayLine += grayBpl;
388+ gmeanLine += gmeanBpl;
389+ bwLine += bwWpl;
390+ }
391+ return bwImg;
392+ } // binarizeGrad
393+
271394BinaryImage binarizeEdgeDiv (const QImage& src,
272395 const QSize windowSize,
273396 const double kep,
@@ -282,6 +405,9 @@ BinaryImage binarizeEdgeDiv(const QImage& src,
282405 }
283406
284407 QImage gray (toGrayscale (src));
408+ if (gray.isNull ()) {
409+ return BinaryImage ();
410+ }
285411 const int w = gray.width ();
286412 const int h = gray.height ();
287413
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