feat: add --mode strip to remove the OCR text layer without rasterizing

Adds a processing mode that removes the invisible (render mode 3) OCR text layer in place. Unlike `--ocr-engine none --force-ocr`, it does not rasterize the page, so images and visible content are preserved unchanged and the output is smaller rather than larger. Options that require rasterization or OCR (--deskew, --clean, --sidecar, etc.) are rejected. Only invisible text is removed; text drawn as visible glyphs under an opaque image (some OCR engines, and OCRmyPDF v2.2 and earlier) cannot be removed this way, as documented. Closes #1435.
2026-06-11 12:34:03 -07:00
parent 8a8d515933
commit 0d4c3bcdcf
8 changed files with 152 additions and 11 deletions
@@ -0,0 +1,71 @@
+# SPDX-FileCopyrightText: 2026 James R. Barlow
+# SPDX-License-Identifier: MPL-2.0
+
+"""Tests for --mode strip (remove the OCR text layer in place)."""
+
+from __future__ import annotations
+
+import pikepdf
+import pytest
+
+from ocrmypdf.exceptions import BadArgsError
+from ocrmypdf.pdfinfo import PdfInfo
+
+from .conftest import check_ocrmypdf, run_ocrmypdf_api
+
+
+def _image_raw_bytes(pdf_path):
+    """Return raw (still-compressed) stream bytes of each image on page 1."""
+    out = []
+    with pikepdf.open(pdf_path) as pdf:
+        resources = pdf.pages[0].get('/Resources', {})
+        for _name, xobj in resources.get('/XObject', {}).items():
+            if xobj.get('/Subtype') == pikepdf.Name.Image:
+                out.append(bytes(xobj.read_raw_bytes()))
+    return out
+
+
+def test_mode_strip_removes_ocr_layer(resources, outpdf):
+    """--mode strip removes the invisible OCR layer without rasterizing.
+
+    The page image is preserved byte-for-byte and the output is no larger than
+    the input.
+    """
+    input_pdf = resources / 'graph_ocred.pdf'
+    assert PdfInfo(input_pdf, detailed_analysis=True)[0].has_text
+
+    out = check_ocrmypdf(
+        input_pdf, outpdf, '--mode', 'strip', '--output-type', 'pdf', '--optimize', '0'
+    )
+
+    info = PdfInfo(out, detailed_analysis=True)
+    assert len(info) == 1, "page count must be unchanged"
+    assert not info[0].has_text, "OCR text layer should be removed"
+    assert _image_raw_bytes(out) == _image_raw_bytes(input_pdf), (
+        "page image must be preserved byte-for-byte (no rasterization)"
+    )
+    assert out.stat().st_size <= input_pdf.stat().st_size, (
+        "removing the text layer must not grow the file"
+    )
+
+
+def test_mode_strip_preserves_visible_text(resources, outpdf):
+    """--mode strip leaves visible/born-digital text untouched (render mode != 3).
+
+    type3_font_nomapping.pdf is born-digital text with no images (the #1608
+    case): its visible text must survive strip, which only removes invisible
+    OCR text.
+    """
+    input_pdf = resources / 'type3_font_nomapping.pdf'
+    out = check_ocrmypdf(
+        input_pdf, outpdf, '--mode', 'strip', '--output-type', 'pdf', '--optimize', '0'
+    )
+    assert PdfInfo(out, detailed_analysis=True)[0].has_text
+
+
+def test_mode_strip_rejects_image_processing_options(resources, no_outpdf):
+    """Options requiring rasterization/OCR are rejected in strip mode."""
+    with pytest.raises(BadArgsError, match=r'--deskew'):
+        run_ocrmypdf_api(
+            resources / 'graph_ocred.pdf', no_outpdf, '--mode', 'strip', '--deskew'
+        )