Clarified some requires clauses

dlib/image_transforms/equalize_histogram.h

@@ -28,7 +28,7 @@ namespace dlib
         COMPILE_TIME_ASSERT( pixel_traits<typename in_image_type::type>::is_unsigned == true );
 
         typedef typename pixel_traits<typename in_image_type::type>::basic_pixel_type in_image_basic_pixel_type;
-        COMPILE_TIME_ASSERT( sizeof(in_image_basic_pixel_type) < sizeof(long));
+        COMPILE_TIME_ASSERT( sizeof(in_image_basic_pixel_type) <= 2);
 
         // make sure hist is the right size
         if (R == 1)
@@ -68,7 +68,7 @@ namespace dlib
         COMPILE_TIME_ASSERT( pixel_traits<typename out_image_type::type>::is_unsigned == true );
 
         typedef typename pixel_traits<typename in_image_type::type>::basic_pixel_type in_image_basic_pixel_type;
-        COMPILE_TIME_ASSERT( sizeof(in_image_basic_pixel_type) < sizeof(long));
+        COMPILE_TIME_ASSERT( sizeof(in_image_basic_pixel_type) <= 2);
 
         typedef typename in_image_type::type in_pixel_type;
         typedef typename out_image_type::type out_pixel_type;

dlib/image_transforms/equalize_histogram_abstract.h

@@ -27,7 +27,7 @@ namespace dlib
             - pixel_traits<typename out_image_type::type>::has_alpha == false 
             - pixel_traits<typename in_image_type::type>::is_unsigned == true 
             - pixel_traits<typename out_image_type::type>::is_unsigned == true 
-            - pixel_traits<typename in_image_type::type>::max() < std::numeric_limits<long>::max() 
+            - pixel_traits<typename in_image_type::type>::max() <= 65535 
         ensures
             - #out_img == the histogram equalized version of in_img
             - #out_img.nc() == in_img.nc()
@@ -63,7 +63,7 @@ namespace dlib
         requires
             - in_image_type == is an implementation of array2d/array2d_kernel_abstract.h
             - pixel_traits<typename in_image_type::type>::is_unsigned == true 
-            - pixel_traits<typename in_image_type::type>::max() < std::numeric_limits<long>::max() 
+            - pixel_traits<typename in_image_type::type>::max() <= 65535 
             - hist must be capable of representing a column vector of length 
               pixel_traits<typename in_image_type>::max(). I.e. if R and C are nonzero
               then they must be values that don't conflict with the previous sentence.

dlib/image_transforms/thresholding_abstract.h

@@ -67,10 +67,11 @@ namespace dlib
         requires
             - in_image_type == is an implementation of array2d/array2d_kernel_abstract.h
             - out_image_type == is an implementation of array2d/array2d_kernel_abstract.h
-            - pixel_traits<typename out_image_type::type>::grayscale == true  
-            - pixel_traits<typename in_image_type::type>::has_alpha == false
-            - pixel_traits<typename out_image_type::type>::has_alpha == false 
+            - pixel_traits<typename in_image_type::type>::max() <= 65535 
+            - pixel_traits<typename in_image_type::type>::has_alpha   == false
             - pixel_traits<typename in_image_type::type>::is_unsigned == true 
+            - pixel_traits<typename out_image_type::type>::grayscale  == true  
+            - pixel_traits<typename out_image_type::type>::has_alpha  == false 
             - pixel_traits<typename out_image_type::type>::is_unsigned == true 
         ensures
             - #out_img == the thresholded version of in_img (in_img is converted to a grayscale