make sure kernel sizes are 1 at least

src/beauty/beauty-demo.cpp

@@ -17,7 +17,7 @@ constexpr bool OFFSCREEN = false;
 constexpr int VA_HW_DEVICE_INDEX = 0;
 constexpr unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
 
-constexpr int BLUR_KERNEL_SIZE = DIAG / 413 % 2 == 0 ? DIAG / 413 + 1 : DIAG / 413;
+constexpr int BLUR_KERNEL_SIZE = std::max(int(DIAG / 413 % 2 == 0 ? DIAG / 413 + 1 : DIAG / 413), 1);
 
 using std::cerr;
 using std::endl;

src/optflow/optflow-demo.cpp

@@ -36,7 +36,7 @@ constexpr float POINT_LOSS = 25;
 // of tracked points and therefor is usually much smaller.
 constexpr int MAX_STROKE = 17;
 // Intensity of glow defined by kernel size. The default scales with the image diagonal.
-constexpr int GLOW_KERNEL_SIZE = DIAG / 138 % 2 == 0 ? DIAG / 138  + 1 : DIAG / 138;
+constexpr int GLOW_KERNEL_SIZE = std::max(int(DIAG / 138 % 2 == 0 ? DIAG / 138  + 1 : DIAG / 138), 1);
 //hue, saturation, lightness and alpha all from 0 to 255
 const cv::Scalar EFFECT_COLOR(26, 255, 153, 7);
 

src/tetra/tetra-demo.cpp

@@ -10,7 +10,7 @@ constexpr const char* OUTPUT_FILENAME = "tetra-demo.mkv";
 constexpr const int VA_HW_DEVICE_INDEX = 0;
 constexpr unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
 
-constexpr int GLOW_KERNEL_SIZE = DIAG / 138 % 2 == 0 ? DIAG / 138 + 1 : DIAG / 138;
+constexpr int GLOW_KERNEL_SIZE = std::max(int(DIAG / 138 % 2 == 0 ? DIAG / 138 + 1 : DIAG / 138), 1);
 
 using std::cerr;
 using std::endl;

src/video/video-demo.cpp

@@ -10,8 +10,7 @@ constexpr bool OFFSCREEN = false;
 constexpr const char *OUTPUT_FILENAME = "video-demo.mkv";
 constexpr unsigned long DIAG = hypot(double(WIDTH), double(HEIGHT));
 
-constexpr int GLOW_KERNEL_SIZE = DIAG / 138 % 2 == 0 ? DIAG / 138 + 1 : DIAG / 138;
-
+constexpr int GLOW_KERNEL_SIZE = std::max(int(DIAG / 138 % 2 == 0 ? DIAG / 138 + 1 : DIAG / 138), 1);
 
 using std::cerr;
 using std::endl;