Changed the default behavior of heatmap() and jet() to use min(mat(img)) as the

lower bound instead of 0 for the case where you don't give any bounds at all.

dlib/image_transforms/colormaps.h

@@ -134,7 +134,7 @@ namespace dlib
     )
     {
         typedef op_heatmap<image_type> op;
-        return matrix_op<op>(op(img,max(mat(img)),0));
+        return matrix_op<op>(op(img,max(mat(img)),min(mat(img))));
     }
 
 // ----------------------------------------------------------------------------------------
@@ -230,7 +230,7 @@ namespace dlib
     )
     {
         typedef op_jet<image_type> op;
-        return matrix_op<op>(op(img,max(mat(img)),0));
+        return matrix_op<op>(op(img,max(mat(img)),min(mat(img))));
     }
 
 // ----------------------------------------------------------------------------------------

dlib/image_transforms/colormaps_abstract.h

@@ -69,7 +69,7 @@ namespace dlib
             - image_type is an implementation of array2d/array2d_kernel_abstract.h
             - pixel_traits<image_type::type> must be defined
         ensures
-            - returns heatmap(img, max(mat(img)), 0)
+            - returns heatmap(img, max(mat(img)), min(mat(img)))
     !*/
 
 // ----------------------------------------------------------------------------------------
@@ -109,7 +109,7 @@ namespace dlib
             - image_type is an implementation of array2d/array2d_kernel_abstract.h
             - pixel_traits<image_type::type> must be defined
         ensures
-            - returns jet(img, max(mat(img)), 0)
+            - returns jet(img, max(mat(img)), min(mat(img)))
     !*/
 
 // ----------------------------------------------------------------------------------------