Reads the codestream's header without decoding the samples.
bool TryReadHeader(ReadOnlySpan<byte> encoded, ImageFilterContext context, scoped out ImageHeader header)
The data the filter would decode.
The image's dictionary values, limits and the filter context.
The image's size and components as the codestream declares them.
false when the header cannot be read; DecodeImage(ReadOnlyMemory<Byte>, ImageFilterContext) is then not called.ISO 32000-2 §7.4.9 (JPEG 2000 dimensions win over the dictionary's).