From 635342ab732c3e1036d67969e1691022db86e2e7 Mon Sep 17 00:00:00 2001
From: wzw <zhiwen.wu@intel.com>
Date: Wed, 5 Jul 2017 21:24:09 +0800
Subject: [PATCH] ocl_calcHist1: Use proper local size for merge_histogram
 kernel

merge_histogram kernel only need "BINS" theads to accumulate the
histgrams, it is not efficient to directly use maxGroupSize as
local size if maxGroupSize is far greater then BINS.
---
 modules/imgproc/src/histogram.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/modules/imgproc/src/histogram.cpp b/modules/imgproc/src/histogram.cpp
index cdd10869db..33f15c5250 100644
--- a/modules/imgproc/src/histogram.cpp
+++ b/modules/imgproc/src/histogram.cpp
@@ -1723,6 +1723,7 @@ static bool ocl_calcHist1(InputArray _src, OutputArray _hist, int ddepth = CV_32
     if (!k1.run(1, &globalsize, &wgs, false))
         return false;
 
+    wgs = std::min<size_t>(ocl::Device::getDefault().maxWorkGroupSize(), BINS);
     char cvt[40];
     ocl::Kernel k2("merge_histogram", ocl::imgproc::histogram_oclsrc,
                    format("-D BINS=%d -D HISTS_COUNT=%d -D WGS=%d -D convertToHT=%s -D HT=%s",