Remove redundant code and clarify restriction when colorspace_type is RGB

Author: JeromeMartinez

ffv1.md

@@ -381,11 +381,6 @@ Background: At the time of this writing, in all known implementations of FFV1 bi
 
 [@!ISO.15444-1.2016]
 
-An FFV1 `Frame` using JPEG2000-RCT MUST use one of the following arrangements:
-
-- Y, Cb, Cr
-- Y, Cb, Cr, Alpha
-
 When FFV1 uses the JPEG2000-RCT, the horizontal lines are interleaved to improve caching efficiency since it is most likely that the RCT will immediately be converted to RGB during decoding. The interleaved coding order is also Y, then Cb, then Cr, and then if used Alpha.
 
 As an example, a `Frame` that is two pixels wide and two pixels high, could be comprised of the following structure:
@@ -1119,6 +1114,9 @@ If state_transition_delta is not present in the FFV1 bitstream, all Range coder
 | 1     | RGB                             | JPEG2000-RCT                    | line then plane                 |
 | Other | reserved for future use         | reserved for future use         | reserved for future use         |
 
+Restrictions:  
+If `colorspace_type` is 1, `chroma_planes` MUST be 1, `h_chroma_subsample` MUST be 1, `v_chroma_subsample` MUST be 1.  
+
 ### chroma_planes
 
 `chroma_planes` indicates if chroma (color) planes are present.
@@ -1128,8 +1126,6 @@ If state_transition_delta is not present in the FFV1 bitstream, all Range coder
 |0      |   chroma planes are not present |
 |1      |   chroma planes are present     |
 
-If interleave method is line then plane, `chroma_planes` MUST be 1.
-
 ### bits_per_raw_sample
 
 `bits_per_raw_sample` indicates the number of bits for each sample. Inferred to be 8 if not present.