Change EXIF Applicability's None to passthrough

This allows it to address the case of copying all EXIF data into a
separate file. And as soon as our decoder can handle files without any
image data (missing any stripoffsets, etc.) in ways that do not return
errors we can hopefully do the opposite and merge the data again.

src/encoder/mod.rs

@@ -777,7 +777,15 @@ impl Default for EncodeMetadataOptions<'_> {
 #[non_exhaustive]
 #[derive(Clone, Copy, Default)]
 pub struct EncodeMetadataApplicability {
+    /// The photometric interpretation of the image data.
+    ///
+    /// If `None` then metadata tags are not filtered, otherwise only tags applicable to the given
+    /// photometric interpretation are recorded.
     pub photometric: Option<PhotometricInterpretation>,
+    /// The planar configuration of the image data.
+    ///
+    /// If `None` then metadata tags are not filtered, otherwise only tags applicable to the given
+    /// configuration are recorded.
     pub planar: Option<PlanarConfiguration>,
 }
 

src/encoder/tag_filter.rs

@@ -169,16 +169,10 @@ impl TagFilter {
             Level::Photometric(photometric) => {
                 match (photometric, target.planar, target.photometric) {
                     (Photometric::All, _, _) => Choice::Ok,
-                    (Photometric::Planar, Some(PlanarConfiguration::Planar), _) => Choice::Ok,
+                    (Photometric::Planar, Some(PlanarConfiguration::Planar) | None, _) => {
-                    (Photometric::Planar, None, _)
-                        if matches!(self.filter_level, FilterLevel::All) =>
-                    {
                         Choice::Ok
                     }
-                    (Photometric::YCbCr, _, Some(PhotometricInterpretation::YCbCr)) => Choice::Ok,
+                    (Photometric::YCbCr, _, Some(PhotometricInterpretation::YCbCr) | None) => {
-                    (Photometric::YCbCr, _, None)
-                        if matches!(self.filter_level, FilterLevel::All) =>
-                    {
                         Choice::Ok
                     }
                     _ => Choice::Discard,