Add rotate 180 correlation sanity check

ocrmypdf/leptonica.py

@@ -201,6 +201,11 @@ def correlation_binary(pix1, pix2):
     return correlation[0]
 
 
+def rotate180(pix):
+    pix_rotated = lept.pixRotate180(ffi.NULL, pix)
+    return ffi.gc(pix_rotated, _pix_destroy)
+
+
 if __name__ == '__main__':
     parser = argparse.ArgumentParser(
         description="Python wrapper to access Leptonica")

ocrmypdf/lib/compile_leptonica.py

@@ -53,6 +53,7 @@ void pixDestroy ( PIX **ppix );
 PIX * pixDeskew ( PIX *pixs, l_int32 redsearch );
 char * getLeptonicaVersion (  );
 l_int32 pixCorrelationBinary(PIX *pix1, PIX *pix2, l_float32 *pval);
+PIX *pixRotate180(PIX *pixd, PIX *pixs);
 """)
 
 if __name__ == '__main__':

tests/test_main.py

@@ -261,10 +261,14 @@ def test_autorotate(spoof_tesseract_cache, renderer):
             xres=100, yres=100, raster_device='pngmono', log=gslog, pageno=1)
 
     pix_ref = leptonica.pixRead(_outfile('reference.png'))
+    pix_ref_180 = leptonica.rotate180(pix_ref)
+    correlation = leptonica.correlation_binary(pix_ref, pix_ref_180)
+    assert correlation < 0.10
+
     for n in range(1, 4+1):
         pix_other = leptonica.pixRead(_outfile('cardinal-%i.png' % n))
-        print(leptonica.correlation_binary(pix_ref, pix_other))
-
+        correlation = leptonica.correlation_binary(pix_ref, pix_other)
+        assert correlation > 0.80
 
 @pytest.mark.parametrize('renderer', [
     'hocr',