file format doc update

terranmon.txt

@@ -500,22 +500,25 @@ Image is divided into 4x4 blocks and each block is serialised, then the entire i
 # File Structure
 \x1F T S V M i P F
 [HEADER]
-[Blocks.gz]
+[Blocks]
 
 - Header
     uint16 WIDTH
     uint16 HEIGHT
-    uint8 HAS ALPHA
+    uint8 Flags
-    uint8  IPF Type
+        0b p00z 000a
-        0: Type 1 (4:2:0 chroma subsampling)
+        - a: has alpha
-        1: Type 2 (4:2:2 chroma subsampling)
+        - z: gzipped (p flag always sets this flag)
+        - p: progressive ordering (Adam7)
+    uint8  iPF Type/Colour Mode
+        0: Type 1 (4:2:0 chroma subsampling; 2048 colours?)
+        1: Type 2 (4:2:2 chroma subsampling; 2048 colours?)
+       16: Type 16 (full RGBA4444; 4096 colours)
     byte[10] RESERVED
-    uint32 UNCOMPRESSED SIZE
+    uint32 UNCOMPRESSED SIZE (somewhat redundant but included for convenience)
 
-- *.gz
+- Chroma Subsampled Blocks
-    literally a .gz of the iPF bytes
+    Gzipped unless the z-flag is not set.
-
-- Blocks
     4x4 pixels are sampled, then divided into YCoCg planes.
     CoCg planes are "chroma subsampled" by 4:2:0, then quantised to 4 bits (8 bits for CoCg combined)
     Y plane is quantised to 4 bits
@@ -565,6 +568,10 @@ Image is divided into 4x4 blocks and each block is serialised, then the entire i
 
     which packs into: [ 30 | 30 | FA | FA ] (because little endian)
 
+- Progressive Blocks
+    Ordered string of words (word size varies by the colour mode) are stored here.
+    If progressive mode is enabled, words are stored in the order that accomodates it.
+
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