minor fix

modules/gpu/src/beliefpropagation_gpu.cpp

@@ -105,7 +105,7 @@ static void stereo_bp_gpu_operator(int ndisp, int iters, int levels, float disc_
     int divisor = (int)pow(2.f, levels - 1.0f);
     int lowest_cols = cols / divisor;
     int lowest_rows = rows / divisor;
-    const int min_image_dim_size = 20;
+    const int min_image_dim_size = 2;
     CV_Assert(min(lowest_cols, lowest_rows) > min_image_dim_size);
 
     u.create(rows * ndisp, cols, CV_32F);