Add RGGB (Bayer) color space and YDgCoCg-R transformation

ffv1.md

@@ -1016,9 +1016,13 @@ Parameters( ) {                                               |
     colorspace_type                                           | ur
     if (version >= 1)                                         |
         bits_per_raw_sample                                   | ur
-    chroma_planes                                             | br
-    log2_h_chroma_subsample                                   | ur
-    log2_v_chroma_subsample                                   | ur
+    if (colorspace_type == 2) {                               |
+        rggb_order                                            | ur
+    } else {                                                  |
+        chroma_planes                                         | br
+        log2_h_chroma_subsample                               | ur
+        log2_v_chroma_subsample                               | ur
+    }                                                         |
     alpha_plane                                               | br
     if (version >= 3) {                                       |
         num_h_slices - 1                                      | ur
@@ -1108,6 +1112,7 @@ If state_transition_delta is not present in the FFV1 bitstream, all Range coder
 |-------|:--------------------------------|:--------------------------------|:--------------------------------|
 | 0     | YCbCr                           | No Pixel transformation         | plane then line                 |
 | 1     | RGB                             | JPEG2000-RCT                    | line then plane                 |
+| 2     | BGGR (Bayer)                    | YDgCoCg-R                       | line then plane                 | 
 | Other | reserved for future use         | reserved for future use         | reserved for future use         |
 
 Restrictions:  
@@ -1137,12 +1142,14 @@ Decoders SHOULD accept and interpret bits_per_raw_sample = 0 as 8.
 ### log2_h_chroma_subsample
 
 PDF:`log2_h_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma width ($chroma\_width=2^{-log2\_h\_chroma\_subsample}luma\_width$).  
-RFC:`log2_h_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma width (`chroma_width = 2^(-log2_h_chroma_subsample) * luma_width`).
+RFC:`log2_h_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma width (`chroma_width = 2^(-log2_h_chroma_subsample) * luma_width`).  
+Inferred to be 0 if not present.  
 
 ### log2_v_chroma_subsample
 
 PDF:`log2_v_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma height ($chroma\_height=2^{-log2\_v\_chroma\_subsample}luma\_height$).  
-RFC:`log2_v_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma height (`chroma_height=2^(-log2_v_chroma_subsample) * luma_height`).
+RFC:`log2_v_chroma_subsample` indicates the subsample factor, stored in powers to which the number 2 must be raised, between luma and chroma height (`chroma_height=2^(-log2_v_chroma_subsample) * luma_height`).  
+Inferred to be 0 if not present.  
 
 ### alpha_plane