fix: support TIFF predictor on image streams (#18)

playa/pdftypes.py

@@ -22,7 +22,7 @@
 from playa.ccitt import ccittfaxdecode
 from playa.lzw import lzwdecode
 from playa.runlength import rldecode
-from playa.utils import apply_png_predictor
+from playa.utils import apply_png_predictor, apply_tiff_predictor
 
 if TYPE_CHECKING:
     from playa.document import Document
@@ -450,6 +450,18 @@ def decode(self, strict: bool = False) -> None:
                 if pred == 1:
                     # no predictor
                     pass
+                elif pred == 2:
+                    # TIFF predictor 2
+                    colors = int_value(params.get("Colors", 1))
+                    columns = int_value(params.get("Columns", 1))
+                    raw_bits_per_component = params.get("BitsPerComponent", 8)
+                    bitspercomponent = int_value(raw_bits_per_component)
+                    data = apply_tiff_predictor(
+                        colors,
+                        columns,
+                        bitspercomponent,
+                        data,
+                    )
                 elif pred >= 10:
                     # PNG predictor
                     colors = int_value(params.get("Colors", 1))

playa/utils.py

@@ -2,7 +2,6 @@
 
 import string
 from typing import (
-    TYPE_CHECKING,
     Any,
     Iterable,
     Iterator,
@@ -14,9 +13,6 @@
 
 from playa.exceptions import PDFSyntaxError
 
-if TYPE_CHECKING:
-    pass
-
 
 def make_compat_bytes(in_str: str) -> bytes:
     """Converts to bytes, encoding to unicode."""
@@ -47,6 +43,33 @@ def paeth_predictor(left: int, above: int, upper_left: int) -> int:
         return upper_left
 
 
+def apply_tiff_predictor(
+    colors: int, columns: int, bitspercomponent: int, data: bytes
+) -> bytes:
+    """Reverse the effect of the TIFF predictor 2
+
+    Documentation: https://www.itu.int/itudoc/itu-t/com16/tiff-fx/docs/tiff6.pdf
+    (Section 14, page 64)
+    """
+    if bitspercomponent != 8:
+        error_msg = f"Unsupported `bitspercomponent': {bitspercomponent}"
+        raise ValueError(error_msg)
+    bpp = colors * (bitspercomponent // 8)
+    nbytes = columns * bpp
+    buf: list[int] = []
+    for scanline_i in range(0, len(data), nbytes):
+        raw: list[int] = []
+        for i in range(nbytes):
+            new_value = data[scanline_i + i]
+            if i >= bpp:
+                new_value += raw[i - bpp]
+                new_value %= 256
+            raw.append(new_value)
+        buf.extend(raw)
+
+    return bytes(buf)
+
+
 def apply_png_predictor(
     pred: int,
     colors: int,

tests/test_open.py

@@ -170,6 +170,13 @@ def test_glyph_offsets() -> None:
             glyph_y = dic["glyph_offset_y"]
 
 
+def test_tiff_predictor() -> None:
+    with playa.open(TESTDIR / "contrib" / "test_pdf_with_tiff_predictor.pdf") as doc:
+        image = next(doc.pages[0].images)
+        # Decoded TIFF: 600 x 600 + a header
+        assert len(image.stream.buffer) == 360600
+
+
 if __name__ == "__main__":
     import logging