From 636623ab493e595a5cca794ca55f6cc0f36bd762 Mon Sep 17 00:00:00 2001 From: Kara Engelhardt Date: Wed, 11 Dec 2024 17:59:25 +0100 Subject: [PATCH] graft: fix invisible text appearing after strip_invisible_text strip_invisible_text resets the text render mode on each `BT` (begin text) command. However the text state is not actually reset for each text element, only for each page. The pdf reference says: > The text state operators can appear outside text objects, and the values they set > are retained across text objects in a single content stream. Like other graphics > state parameters, these parameters are initialized to their default values at the > beginning of each page. > > -- https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf#page=397 With the current implementation, a text object is only deleted if it contains a `3 Tr` command (setting the text rendering mode to invalid). However the rendering mode may be set once and then not changed for multiple text objects or set outside of a text object. In that case only the first text object (which contains the `3 Tr`-command) is removed. This not only leaves the other text objects in the pdf, but also makes them visible, since the text object that contained the `3 Tr`-command is removed. This PR updates `strip_invisible_text` to not reset the rendering mode for each object and to keep track of the rendering mode when the graphic state is pushed/popped. --- src/ocrmypdf/_graft.py | 17 ++++++++--- tests/test_graft.py | 69 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 81 insertions(+), 5 deletions(-) diff --git a/src/ocrmypdf/_graft.py b/src/ocrmypdf/_graft.py index 1848e8840..7d6f2cba1 100644 --- a/src/ocrmypdf/_graft.py +++ b/src/ocrmypdf/_graft.py @@ -57,27 +57,34 @@ def _update_resources( fonts[font_key] = font + def strip_invisible_text(pdf: Pdf, page: Page): stream = [] in_text_obj = False - render_mode = 0 + render_mode_stack = [0] text_objects = [] for operands, operator in parse_content_stream(page, ''): + if operator == Operator('Tr'): + render_mode_stack[-1] = operands[0] + + if operator == Operator('q'): + render_mode_stack.append(render_mode_stack[-1]) + + if operator == Operator('Q'): + render_mode_stack.pop() + if not in_text_obj: if operator == Operator('BT'): in_text_obj = True - render_mode = 0 text_objects.append((operands, operator)) else: stream.append((operands, operator)) else: - if operator == Operator('Tr'): - render_mode = operands[0] text_objects.append((operands, operator)) if operator == Operator('ET'): in_text_obj = False - if render_mode != 3: + if render_mode_stack[-1] != 3: stream.extend(text_objects) text_objects.clear() diff --git a/tests/test_graft.py b/tests/test_graft.py index eaaac3a8d..02693b655 100644 --- a/tests/test_graft.py +++ b/tests/test_graft.py @@ -40,3 +40,72 @@ def test_links(resources, outpdf): p2 = pdf.pages[1] assert p1.Annots[0].A.D[0].objgen == p2.objgen assert p2.Annots[0].A.D[0].objgen == p1.objgen + + +def test_strip_invisble_text(): + pdf = pikepdf.Pdf.new() + print(pikepdf.parse_content_stream(pikepdf.Stream(pdf, b'3 Tr'))) + page = pdf.add_blank_page() + visible_text = [ + pikepdf.ContentStreamInstruction((), pikepdf.Operator('BT')), + pikepdf.ContentStreamInstruction( + (pikepdf.Name('/F0'), 12), pikepdf.Operator('Tf') + ), + pikepdf.ContentStreamInstruction((288, 720), pikepdf.Operator('Td')), + pikepdf.ContentStreamInstruction( + (pikepdf.String('visible'),), pikepdf.Operator('Tj') + ), + pikepdf.ContentStreamInstruction((), pikepdf.Operator('ET')), + ] + invisible_text = [ + pikepdf.ContentStreamInstruction((), pikepdf.Operator('BT')), + pikepdf.ContentStreamInstruction( + (pikepdf.Name('/F0'), 12), pikepdf.Operator('Tf') + ), + pikepdf.ContentStreamInstruction((288, 720), pikepdf.Operator('Td')), + pikepdf.ContentStreamInstruction( + (pikepdf.String('invisible'),), pikepdf.Operator('Tj') + ), + pikepdf.ContentStreamInstruction((), pikepdf.Operator('ET')), + ] + invisible_text_setting_tr = [ + pikepdf.ContentStreamInstruction((), pikepdf.Operator('BT')), + pikepdf.ContentStreamInstruction([3], pikepdf.Operator('Tr')), + pikepdf.ContentStreamInstruction( + (pikepdf.Name('/F0'), 12), pikepdf.Operator('Tf') + ), + pikepdf.ContentStreamInstruction((288, 720), pikepdf.Operator('Td')), + pikepdf.ContentStreamInstruction( + (pikepdf.String('invisible'),), pikepdf.Operator('Tj') + ), + pikepdf.ContentStreamInstruction((), pikepdf.Operator('ET')), + ] + stream = [ + pikepdf.ContentStreamInstruction([], pikepdf.Operator('q')), + pikepdf.ContentStreamInstruction([3], pikepdf.Operator('Tr')), + *invisible_text, + pikepdf.ContentStreamInstruction([], pikepdf.Operator('Q')), + *visible_text, + *invisible_text_setting_tr, + *invisible_text, + ] + content_stream = pikepdf.unparse_content_stream(stream) + page.Contents = pikepdf.Stream(pdf, content_stream) + + def count(string, page): + return len( + [ + True + for operands, operator in pikepdf.parse_content_stream(page) + if operator == pikepdf.Operator('Tj') + and operands[0] == pikepdf.String(string) + ] + ) + + nr_visible_pre = count('visible', page) + ocrmypdf._graft.strip_invisible_text(pdf, page) + nr_visible_post = count('visible', page) + assert ( + nr_visible_pre == nr_visible_post + ), 'Number of visible text elements did not change' + assert count('invisible', page) == 0, 'No invisible elems left'