diff --git a/stim/envi/hsi.h b/stim/envi/hsi.h
index 1788cd3..c9c5ef4 100644
--- a/stim/envi/hsi.h
+++ b/stim/envi/hsi.h
@@ -149,13 +149,13 @@ public:
 			for(size_t i = 0; i < R[0] * R[1]; i++){		//for each pixel in that page
 
 #ifdef _WIN32
-				if(!_finite(page[i])){						//if the value at index i is finite
+				if(!_finite(page[i])){						//if the value at index i is not finite
 #else
-				if(!std::isfinite(page[i])){					//C++11 implementation
+				if(!std::isfinite(page[i])){				//C++11 implementation
 #endif
 					size_t x, y, b;
-					xyb(p * R[0] * R[1] + i, x, y, b);							//find the 3D coordinates of the value
-					mask[ y * X() + x ] = 0;				//mask the pixel (it's not bad)
+					xyb(p * R[0] * R[1] + i, x, y, b);		//find the 3D coordinates of the value
+					mask[ y * X() + x ] = 0;				//remove the pixel (it's bad)
 				}
 			}
 			if(PROGRESS) progress = (double)(p + 1) / (double)R[2] * 100;
--
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