Added the jet color scheme.

dlib/image_transforms/colormaps.h

@@ -125,6 +125,90 @@ namespace dlib
         return matrix_op<op>(op(img,max_val,min_val));
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct op_jet : does_not_alias 
+    {
+        op_jet( 
+            const T& img_,
+            const double max_val_,
+            const double min_val_
+            ) : img(img_), max_val(max_val_), min_val(min_val_){}
+
+        const T& img;
+
+        const double max_val;
+        const double min_val;
+
+        const static long cost = 7;
+        const static long NR = 0;
+        const static long NC = 0;
+        typedef rgb_pixel type;
+        typedef const rgb_pixel const_ret_type;
+        typedef typename T::mem_manager_type mem_manager_type;
+        typedef row_major_layout layout_type;
+
+        const_ret_type apply (long r, long c ) const 
+        { 
+            // scale the gray value into the range [0, 8]
+            const double gray = 8*put_in_range(0, 1, (get_pixel_intensity(img[r][c]) - min_val)/(max_val-min_val));
+            rgb_pixel pix;
+            // s is the slope of color change
+            const double s = 1.0/2.0;
+
+            if (gray <= 1)
+            {
+                pix.red = 0;
+                pix.green = 0;
+                pix.blue = static_cast<unsigned char>((gray+1)*s*255 + 0.5);
+            }
+            else if (gray <= 3)
+            {
+                pix.red = 0;
+                pix.green = static_cast<unsigned char>((gray-1)*s*255 + 0.5);
+                pix.blue = 255;
+            }
+            else if (gray <= 5)
+            {
+                pix.red = static_cast<unsigned char>((gray-3)*s*255 + 0.5);
+                pix.green = 255;
+                pix.blue = static_cast<unsigned char>((5-gray)*s*255 + 0.5);
+            }
+            else if (gray <= 7)
+            {
+                pix.red = 255;
+                pix.green = static_cast<unsigned char>((7-gray)*s*255 + 0.5);
+                pix.blue = 0;
+            }
+            else
+            {
+                pix.red = static_cast<unsigned char>((9-gray)*s*255 + 0.5);
+                pix.green = 0;
+                pix.blue = 0;
+            }
+
+            return pix;
+        }
+
+        long nr () const { return img.nr(); }
+        long nc () const { return img.nc(); }
+    }; 
+
+    template <
+        typename image_type
+        >
+    const matrix_op<op_jet<image_type> >  
+    jet (
+        const image_type& img,
+        double max_val,
+        double min_val = 0
+    )
+    {
+        typedef op_jet<image_type> op;
+        return matrix_op<op>(op(img,max_val,min_val));
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/image_transforms/colormaps_abstract.h

@@ -54,6 +54,29 @@ namespace dlib
             - The returned matrix will have the same dimensions as img.
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename image_type
+        >
+    const matrix_exp jet (
+        const image_type& img,
+        double max_val,
+        double min_val = 0
+    );
+    /*!
+        requires
+            - image_type is an implementation of array2d/array2d_kernel_abstract.h
+            - pixel_traits<image_type::type> must be defined
+        ensures
+            - Interprets img as a grayscale image and returns a new matrix which represents
+              a colored version of img.  In particular, the colors will depict img using a
+              jet color scheme where pixels with a value <= min_val are dark blue and
+              larger pixel values become light blue, then yellow, and then finally red as
+              they approach max_Val.
+            - The returned matrix will have the same dimensions as img.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }