feat: decode old-style (pre-TIFF-6.0) LZW streams

tests/decode_images.rs

@@ -1060,6 +1060,16 @@ fn test_gray_u12_hpredict() {
     test_image_sum_u16("hpredict-1c-12b.tiff", ColorType::Gray(12), 11000);
 }
 
+// ---- Old-style LZW ----
+
+#[test]
+fn test_old_style_lzw() {
+    // Pre-TIFF-6.0 "old-style" LZW: LSB-first bit order with no early-change size
+    // switch. Auto-detected from the stream (first byte 0x00, second byte odd).
+    // Same image as libtiffpic's quad-lzw.tif; the decoded pixels must match.
+    test_image_sum_u8("quad-lzw-compat.tiff", ColorType::RGB(8), 21048924);
+}
+
 // ---- TransparencyMask ----
 
 /// Build a minimal uncompressed 2x2 TIFF in memory, in the requested byte order,

tests/decode_libtiffpic.rs

@@ -190,7 +190,7 @@ const FILES: &[(&str, Option<u32>)] = &[
     ("tests/libtiffpic/oxford.tif", Some(0x355d2e3e)),
     ("tests/libtiffpic/pc260001.tif", Some(0xdb56b753)),
     ("tests/libtiffpic/quad-jpeg.tif", Some(0xcba22475)),
-    ("tests/libtiffpic/quad-lzw.tif", Some(0)), // invalid LZW stream
+    ("tests/libtiffpic/quad-lzw.tif", Some(0x6055f9ee)), // old-style (LSB) LZW
     ("tests/libtiffpic/quad-tile.tif", Some(0x6055f9ee)),
     ("tests/libtiffpic/README", None),
     ("tests/libtiffpic/smallliz.tif", Some(0)), // unsupported YCbCr chroma subsampling