fixed some typos

dlib/image_transforms/spatial_filtering_abstract.h

@@ -51,9 +51,9 @@ namespace dlib
                 - The filter is applied to each color channel independently.
             - if (use_abs == true) then
                 - pixel values after filtering that are < 0 are converted to their absolute values.
-            - The filter is applied such that it is centered over the pixel it writes its
+            - The filter is applied such that it's centered over the pixel it writes its
               output into.  For centering purposes, we consider the center element of the
-              filter to be filter((filter.nr()-1)/2,(filter.nc-1)/2).
+              filter to be filter((filter.nr()-1)/2,(filter.nc()-1)/2).
             - Pixels close enough to the edge of in_img to not have the filter still fit 
               inside the image are always set to zero.
             - #out_img.nc() == in_img.nc()
@@ -115,7 +115,7 @@ namespace dlib
                 - The filter is applied to each color channel independently.
             - if (use_abs == true) then
                 - pixel values after filtering that are < 0 are converted to their absolute values
-            - The filter is applied such that it is centered over the pixel it writes its
+            - The filter is applied such that it's centered over the pixel it writes its
               output into.  For centering purposes, we consider the center element of the
               filter to be FILT((col_filter.size()-1)/2,(row_filter.size()-1)/2).
             - Pixels close enough to the edge of in_img to not have the filter still fit