Fixed a bug in the png_loader. If you loaded an image with an

alpha channel into something without an alpha channel there were
uninitialized values being alpha blended into the image.

dlib/image_loader/png_loader.h

@@ -100,6 +100,9 @@ namespace dlib
             }
             else if (is_rgba() && bit_depth_ == 8)
             {
+                if (!pixel_traits<typename T::type>::has_alpha)
+                    assign_all_pixels(t,0);
+
                 for ( unsigned n = 0; n < height_;n++ )
                 {
                     const unsigned char* v = get_row( n );
@@ -116,6 +119,9 @@ namespace dlib
             }
             else if (is_rgba() && bit_depth_ == 16)
             {
+                if (!pixel_traits<typename T::type>::has_alpha)
+                    assign_all_pixels(t,0);
+
                 for ( unsigned n = 0; n < height_;n++ )
                 {
                     const uint16* v = (uint16*)get_row( n );

dlib/test/image.cpp

@@ -166,7 +166,10 @@ namespace
 #ifdef DLIB_PNG_SUPPORT
         {
             array2d<rgb_alpha_pixel> img;
+            array2d<rgb_pixel> img2, img3;
             img.set_size(14,15);
+            img2.set_size(img.nr(),img.nc());
+            img3.set_size(img.nr(),img.nc());
             for (long r = 0; r < 14; ++r)
             {
                 for (long c = 0; c < 15; ++c)
@@ -189,6 +192,11 @@ namespace
             DLIB_TEST(img.nr() == 14);
             DLIB_TEST(img.nc() == 15);
 
+            assign_all_pixels(img2, 255);
+            assign_all_pixels(img3, 0);
+            load_png(img2, "test.png");
+            assign_image(img3, img);
+
             for (long r = 0; r < 14; ++r)
             {
                 for (long c = 0; c < 15; ++c)
@@ -197,6 +205,10 @@ namespace
                     DLIB_TEST(img[r][c].green == r*14 + c + 2);
                     DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                     DLIB_TEST(img[r][c].alpha == r*14 + c + 4);
+
+                    DLIB_TEST(img2[r][c].red == img3[r][c].red);
+                    DLIB_TEST(img2[r][c].green == img3[r][c].green);
+                    DLIB_TEST(img2[r][c].blue == img3[r][c].blue);
                 }
             }
         }