Removed the requirement that you load dng files into an image of the exact

pixel type that created the file.  Now you can use any pixel type.  I also
changed the code so that grayscale pixels with more than 16 bits get saved as
16 bit grayscale images instead of 8 bit images.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403586

dlib/image_loader/image_loader.h

@@ -588,11 +588,6 @@ namespace dlib
             switch (type)
             {
                 case rgb_alpha_paeth:
-                    if (get_pixel_type<image_type>() != rgb_alpha)
-                    {
-                        image.clear();
-                        throw image_load_error("You have tried to load a dng file that contains rgb_alpha_pixel data into an incompatible pixel type");
-                    }
 
                     for (long r = 0; r < image.nr(); ++r)
                     {
@@ -617,11 +612,6 @@ namespace dlib
                     break;
 
                 case rgb_alpha:
-                    if (get_pixel_type<image_type>() != rgb_alpha)
-                    {
-                        image.clear();
-                        throw image_load_error("You have tried to load a dng file that contains rgb_alpha_pixel data into an incompatible pixel type");
-                    }
 
                     for (long r = 0; r < image.nr(); ++r)
                     {
@@ -646,11 +636,6 @@ namespace dlib
                     break;
 
                 case rgb_paeth:
-                    if (get_pixel_type<image_type>() != rgb)
-                    {
-                        image.clear();
-                        throw image_load_error("You have tried to load a dng file that contains rgb_pixel data into an incompatible pixel type");
-                    }
 
                     for (long r = 0; r < image.nr(); ++r)
                     {
@@ -672,11 +657,6 @@ namespace dlib
                     break;
 
                 case rgb:
-                    if (get_pixel_type<image_type>() != rgb)
-                    {
-                        image.clear();
-                        throw image_load_error("You have tried to load a dng file that contains rgb_pixel data into an incompatible pixel type");
-                    }
 
                     for (long r = 0; r < image.nr(); ++r)
                     {
@@ -698,11 +678,6 @@ namespace dlib
                     break;
 
                 case hsi:
-                    if (get_pixel_type<image_type>() != hsi)
-                    {
-                        image.clear();
-                        throw image_load_error("You have tried to load a dng file that contains hsi_pixel data into an incompatible pixel type");
-                    }
 
                     for (long r = 0; r < image.nr(); ++r)
                     {
@@ -725,10 +700,6 @@ namespace dlib
 
                 case grayscale:
                     {
-                        // An 8bit grayscale image should load successfully into any type of pixel since 
-                        // the assign_pixel() function converts perfectly between this pixel type and all
-                        // others.
-
                         unsigned char p;
                         for (long r = 0; r < image.nr(); ++r)
                         {
@@ -745,12 +716,6 @@ namespace dlib
 
                 case grayscale_16bit:
                     {
-                        if (get_pixel_type<image_type>() != grayscale_16bit)
-                        {
-                            image.clear();
-                            throw image_load_error("You have tried to load a dng file that contains 16bit grayscale data into an incompatible pixel type");
-                        }
-
                         uint16 p;
                         for (long r = 0; r < image.nr(); ++r)
                         {

dlib/image_loader/image_loader_abstract.h

@@ -37,6 +37,9 @@ namespace dlib
             - #image[0][0] will be the upper left corner of the image 
             - #image[image.nr()-1][image.nc()-1] will be the lower right
               corner of the image
+            - Performs any color space conversion necessairy to convert the
+              BMP image data into the pixel type used by the given image
+              object.
         throws
             - image_load_error
                 This exception is thrown if there is an error that prevents us
@@ -73,6 +76,9 @@ namespace dlib
             - #image[0][0] will be the upper left corner of the image 
             - #image[image.nr()-1][image.nc()-1] will be the lower right
               corner of the image
+            - Performs any color space conversion necessairy to convert the
+              dng image data into the pixel type used by the given image
+              object.
         throws
             - image_load_error
                 This exception is thrown if there is an error that prevents us

dlib/image_saver/dng_shared.h

@@ -20,24 +20,9 @@ namespace dlib
             rgb_paeth,
             rgb_alpha,
             rgb_alpha_paeth,
-            grayscale_16bit,
+            grayscale_16bit
         };
 
-        template <typename image_type>
-        int get_pixel_type()
-        {
-            if (pixel_traits<typename image_type::type>::grayscale == true && sizeof(typename image_type::type) == 2)
-                return grayscale_16bit;
-            else if (pixel_traits<typename image_type::type>::grayscale == true && sizeof(typename image_type::type) == 1)
-                return grayscale_16bit;
-            else if (pixel_traits<typename image_type::type>::rgb == true)
-                return rgb;
-            else if (pixel_traits<typename image_type::type>::hsi == true)
-                return hsi;
-            else if (pixel_traits<typename image_type::type>::rgb_alpha == true)
-                return rgb_alpha;
-        }
-
         const unsigned long dng_magic_byte = 100;
 
         template <typename T>

dlib/image_saver/image_saver.h

@@ -241,13 +241,13 @@ namespace dlib
         template <
             typename image_type,
             int pixel_type = static_switch <
-                pixel_traits<typename image_type::type>::grayscale && sizeof(typename image_type::type) != 2,
+                pixel_traits<typename image_type::type>::grayscale && sizeof(typename image_type::type) == 1,
                 pixel_traits<typename image_type::type>::rgb,
                 pixel_traits<typename image_type::type>::hsi,
                 false,
                 pixel_traits<typename image_type::type>::rgb_alpha,
                 false,
-                pixel_traits<typename image_type::type>::grayscale && sizeof(typename image_type::type) == 2
+                pixel_traits<typename image_type::type>::grayscale && sizeof(typename image_type::type) != 1
                 >::value
             >
         struct save_dng_helper;