Add support for IEEEFP Gray(32) decoding

tests/decode_images.rs

@@ -32,6 +32,7 @@ test_image_sum!(test_image_sum_u8, U8, u64);
 test_image_sum!(test_image_sum_u16, U16, u64);
 test_image_sum!(test_image_sum_u32, U32, u64);
 test_image_sum!(test_image_sum_u64, U64, u64);
+test_image_sum!(test_image_sum_f32, F32, f32);
 
 /// Tests that a decoder can be constructed for an image and the color type
 /// read from the IFD and is of the appropriate type, but the type is
@@ -82,6 +83,11 @@ fn test_gray_u64() {
     test_image_sum_u64("gradient-1c-64b.tiff", ColorType::Gray(64), 549892913787);
 }
 
+#[test]
+fn test_gray_f32() {
+    test_image_sum_f32("gradient-1c-32b-float.tiff", ColorType::Gray(32), 128.03194);
+}
+
 #[test]
 fn test_rgb_u8() {
     test_image_sum_u8("rgb-3c-8b.tiff", ColorType::RGB(8), 7842108);