fix

modules/core/include/opencv2/core/ocl.hpp

@@ -489,6 +489,7 @@ public:
     bool runTask(bool sync, const Queue& q=Queue());
 
     size_t workGroupSize() const;
+    size_t preferedWorkGroupSizeMultiple() const;
     bool compileWorkGroupSize(size_t wsz[]) const;
     size_t localMemSize() const;
 

modules/core/src/ocl.cpp

@@ -2813,6 +2813,16 @@ size_t Kernel::workGroupSize() const
                                     sizeof(val), &val, &retsz) >= 0 ? val : 0;
 }
 
+size_t Kernel::preferedWorkGroupSizeMultiple() const
+{
+    if(!p)
+        return 0;
+    size_t val = 0, retsz = 0;
+    cl_device_id dev = (cl_device_id)Device::getDefault().ptr();
+    return clGetKernelWorkGroupInfo(p->handle, dev, CL_KERNEL_PREFERRED_WORK_GROUP_SIZE_MULTIPLE,
+                                    sizeof(val), &val, &retsz) >= 0 ? val : 0;
+}
+
 bool Kernel::compileWorkGroupSize(size_t wsz[]) const
 {
     if(!p || !wsz)

modules/imgproc/src/clahe.cpp

@@ -51,12 +51,14 @@ namespace clahe
         const int tilesX, const int tilesY, const cv::Size tileSize,
         const int clipLimit, const float lutScale)
     {
+        cv::ocl::Kernel _k("calcLut", cv::ocl::imgproc::clahe_oclsrc);
+
         bool is_cpu = cv::ocl::Device::getDefault().type() == cv::ocl::Device::TYPE_CPU;
         cv::String opts;
         if(is_cpu)
             opts = "-D CPU ";
         else
-            opts = cv::format("-D WAVE_SIZE=%d", cv::ocl::Device::getDefault().maxWorkGroupSize());
+            opts = cv::format("-D WAVE_SIZE=%d", _k.preferedWorkGroupSizeMultiple());
 
         cv::ocl::Kernel k("calcLut", cv::ocl::imgproc::clahe_oclsrc, opts);
         if(k.empty())