Optional
BitOptional
BitsOptional
BMPOptional
ColorOptional
CommentOptional
CompressionOptional
CurrentOptional
DirectoryOptional
EncodingOptional
ExifOptional
FileOptional
FileOptional
FileOptional
FileOptional
FileOptional
FileOptional
FileOptional
FileOptional
FileOptional
ImageOptional
ImageOptional
ImageOptional
ImageOptional
MIMEOptional
NumOptional
NumOptional
PixelsOptional
PixelsOptional
PlanesOptional
PreviewOptional
Y
These tags are not metadata fields, but are intrinsic to the content of a given file. ExifTool can't write to many of these tags.