add alpha parameter to ELU layer

modules/dnn/include/opencv2/dnn/all_layers.hpp

@@ -453,6 +453,8 @@ CV__DNN_EXPERIMENTAL_NS_BEGIN
     class CV_EXPORTS ELULayer : public ActivationLayer
     {
     public:
+        float alpha;
+
         static Ptr<ELULayer> create(const LayerParams &params);
     };
 

modules/dnn/src/layers/elementwise_layers.cpp

@@ -740,6 +740,9 @@ const char* const SigmoidFunctor::BaseDefaultFunctor<SigmoidFunctor>::ocl_kernel
 struct ELUFunctor : public BaseDefaultFunctor<ELUFunctor>
 {
     typedef ELULayer Layer;
+    float alpha;
+
+    explicit ELUFunctor(float alpha_ = 1.f) : alpha(alpha_) {}
 
     bool supportBackend(int backendId, int)
     {
@@ -749,14 +752,19 @@ struct ELUFunctor : public BaseDefaultFunctor<ELUFunctor>
 
     inline float calculate(float x) const
     {
-        return x >= 0.f ? x : exp(x) - 1.f;
+        return x >= 0.f ? x : alpha * (exp(x) - 1.f);
+    }
+
+    inline void setKernelParams(ocl::Kernel& kernel) const
+    {
+        kernel.set(3, alpha);
     }
 
 #ifdef HAVE_HALIDE
     void attachHalide(const Halide::Expr& input, Halide::Func& top)
     {
         Halide::Var x("x"), y("y"), c("c"), n("n");
-        top(x, y, c, n) = select(input >= 0.0f, input, exp(input) - 1);
+        top(x, y, c, n) = select(input >= 0.0f, input, alpha * (exp(input) - 1));
     }
 #endif  // HAVE_HALIDE
 
@@ -770,7 +778,7 @@ struct ELUFunctor : public BaseDefaultFunctor<ELUFunctor>
 #ifdef HAVE_DNN_NGRAPH
     std::shared_ptr<ngraph::Node> initNgraphAPI(const std::shared_ptr<ngraph::Node>& node)
     {
-        return std::make_shared<ngraph::op::Elu>(node, 1.0);
+        return std::make_shared<ngraph::op::Elu>(node, alpha);
     }
 #endif  // HAVE_DNN_NGRAPH
 
@@ -1263,8 +1271,10 @@ Ptr<SigmoidLayer> SigmoidLayer::create(const LayerParams& params)
 
 Ptr<ELULayer> ELULayer::create(const LayerParams& params)
 {
-    Ptr<ELULayer> l(new ElementWiseLayer<ELUFunctor>(ELUFunctor()));
+    float alpha = params.get<float>("alpha", 1.0f);
+    Ptr<ELULayer> l(new ElementWiseLayer<ELUFunctor>(ELUFunctor(alpha)));
     l->setParamsFrom(params);
+    l->alpha = alpha;
 
     return l;
 }

modules/dnn/src/opencl/activations.cl

@@ -131,13 +131,14 @@ __kernel void PowForward(const int n, __global const T* in, __global T* out,
     out[index] = pow(shift + scale * in[index], power);
 }
 
-__kernel void ELUForward(const int n, __global const T* in, __global T* out)
+__kernel void ELUForward(const int n, __global const T* in, __global T* out,
+                         const KERNEL_ARG_DTYPE alpha)
 {
   int index = get_global_id(0);
   if (index < n)
   {
     T src = in[index];
-    out[index] = (src >= 0.f) ? src : exp(src) - 1;
+    out[index] = (src >= 0.f) ? src : alpha * (exp(src) - 1);
   }
 }