fix: multi-page image support (tiff) (#1928)

* Initial plan

* Fix multi-page TIFF image support

Co-authored-by: cau-git <60343111+cau-git@users.noreply.github.com>

* add RGB conversion

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Remove pointless test

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Add multi-page TIFF test data and verification tests

Co-authored-by: cau-git <60343111+cau-git@users.noreply.github.com>

* Revert "Add multi-page TIFF test data and verification tests"

This reverts commit 130a10e2d9.

* Proper test for 2 page tiff file

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* DCO Remediation Commit for copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

I, copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>, hereby add my Signed-off-by to this commit: 420df478f3
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I, Christoph Auer <cau@zurich.ibm.com>, hereby add my Signed-off-by to this commit: 6aa85cc933
I, copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>, hereby add my Signed-off-by to this commit: 130a10e2d9
I, Christoph Auer <cau@zurich.ibm.com>, hereby add my Signed-off-by to this commit: d571f36299
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Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

* Proper test for 2 page tiff file (2)

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>

---------

Signed-off-by: Christoph Auer <cau@zurich.ibm.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: cau-git <60343111+cau-git@users.noreply.github.com>
Co-authored-by: Christoph Auer <cau@zurich.ibm.com>

docling/backend/pdf_backend.py

@@ -57,7 +57,31 @@ class PdfDocumentBackend(PaginatedDocumentBackend):
             if self.input_format is InputFormat.IMAGE:
                 buf = BytesIO()
                 img = Image.open(self.path_or_stream)
-                img.save(buf, "PDF")
+
+                # Handle multi-page TIFF images
+                if hasattr(img, "n_frames") and img.n_frames > 1:
+                    # Extract all frames from multi-page image
+                    frames = []
+                    try:
+                        for i in range(img.n_frames):
+                            img.seek(i)
+                            frame = img.copy().convert("RGB")
+                            frames.append(frame)
+                    except EOFError:
+                        pass
+
+                    # Save as multi-page PDF
+                    if frames:
+                        frames[0].save(
+                            buf, "PDF", save_all=True, append_images=frames[1:]
+                        )
+                    else:
+                        # Fallback to single page if frame extraction fails
+                        img.convert("RGB").save(buf, "PDF")
+                else:
+                    # Single page image - convert to RGB and save
+                    img.convert("RGB").save(buf, "PDF")
+
                 buf.seek(0)
                 self.path_or_stream = buf
             else:

tests/test_input_doc.py

@@ -243,3 +243,26 @@ def _make_input_doc_from_stream(doc_stream):
         backend=PdfFormatOption().backend,  # use default
     )
     return in_doc
+
+
+def test_tiff_two_pages():
+    tiff_path = Path("./tests/data/tiff/2206.01062.tif")
+    doc = InputDocument(
+        path_or_stream=tiff_path,
+        format=InputFormat.IMAGE,
+        backend=PdfFormatOption().backend,  # use default backend
+    )
+    assert doc.valid is True
+    assert doc.page_count == 2
+
+    # Expect two full-page rectangles
+    rects_page1 = doc._backend.load_page(0).get_bitmap_rects()
+    rects_page2 = doc._backend.load_page(1).get_bitmap_rects()
+
+    page1_rect = next(rects_page1)
+    page2_rect = next(rects_page2)
+
+    assert page1_rect.t == page2_rect.t == 0
+    assert page1_rect.l == page2_rect.l == 0
+    assert page1_rect.r == page2_rect.r == 612.0
+    assert page1_rect.b == page2_rect.b == 792.0