From 93a9cf84e9ba742af7fe4d579706cbd53b0197fc Mon Sep 17 00:00:00 2001
From: boolli <ll024@bucknell.edu>
Date: Mon, 29 Feb 2016 15:35:12 -0500
Subject: [PATCH] Optimize the GPU grayscale transformation a little bit, but it's still slower than the CPU version

---
 openbr/plugins/cuda/cudargb2grayscale.cu | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/openbr/plugins/cuda/cudargb2grayscale.cu b/openbr/plugins/cuda/cudargb2grayscale.cu
index ba10b80..266389c 100644
--- a/openbr/plugins/cuda/cudargb2grayscale.cu
+++ b/openbr/plugins/cuda/cudargb2grayscale.cu
@@ -19,22 +19,22 @@ namespace br{ namespace cuda {
     int rowInd = blockIdx.y*blockDim.y+threadIdx.y;
     int colInd = blockIdx.x*blockDim.x+threadIdx.x;
     int index = rowInd*cols + colInd;
-    if (rowInd < 1 || rowInd >= rows-1 || colInd < 1 || colInd >= cols-1) {
-      if (rowInd >= rows || colInd >= cols) {
-        return;
-      } else {
-        return;
-      }
+    if (rowInd < 0 || rowInd >= rows || colInd < 0 || colInd >= cols) {
+      return;
     }
+    int new_index = 3 * index;
+    float g = (float) srcPtr[new_index];
+    float b = (float) srcPtr[new_index+1];
+    float r = (float) srcPtr[new_index+2];
 
-    dstPtr[index] = 0.299f * srcPtr[3*index] + 0.587f * srcPtr[3*index+1] + 0.114f * srcPtr[3*index+2];
+    dstPtr[index] = (uint8_t) (0.299f * g + 0.587f * b + 0.114f * r);
     return;
   }
 
   void cudargb2grayscale_wrapper(void* srcPtr, void** dstPtr, int rows, int cols)
   {
     cudaError_t err;
-    dim3 threadsPerBlock(8, 8);
+    dim3 threadsPerBlock(9, 9);
     dim3 numBlocks(cols/threadsPerBlock.x + 1,
                    rows/threadsPerBlock.y + 1);
     CUDA_SAFE_MALLOC(dstPtr, rows*cols*sizeof(uint8_t), &err);
--
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