Drop support for Ghostscript <9.50

docs/installation.rst

@@ -616,8 +616,8 @@ manager. ``pip`` cannot provide them.
 
 The following versions are required:
 
--  Python 3.7 or newer
--  Ghostscript 9.23 or newer
+-  Python 3.8 or newer
+-  Ghostscript 9.50 or newer
 -  Tesseract 4.0.0 or newer
 -  jbig2enc 0.29 or newer
 -  pngquant 2.5 or newer

docs/introduction.rst

@@ -190,8 +190,7 @@ Ghostscript also imposes some limitations:
    behavior can be suppressed by setting ``--pdfa-image-compression`` to
    ``jpeg`` or ``lossless`` to set all images to one type or the other.
    Ghostscript has no option to maintain the input image's format.
-   (Ghostscript 9.25+ can copy JPEG images without transcoding them;
-   earlier versions will transcode.)
+   (Modern Ghostscript can copy JPEG images without transcoding them.)
 -  Ghostscript's PDF/A conversion removes any XMP metadata that is not
    one of the standard XMP metadata namespaces for PDFs. In particular,
    PRISM Metdata is removed.

src/ocrmypdf/_exec/ghostscript.py

@@ -47,21 +47,6 @@ def version():
     return get_version(GS)
 
 
-def jpeg_passthrough_available() -> bool:
-    """Returns True if the installed version of Ghostscript supports JPEG passthru
-
-    Prior to 9.23, Ghostscript decoded and re-encoded JPEGs internally. In 9.23
-    it gained the ability to keep JPEGs unmodified. However, the 9.23
-    implementation was buggy and would deletes the last two bytes of images in
-    some cases, as reported here.
-    https://bugs.ghostscript.com/show_bug.cgi?id=699216
-
-    The issue was fixed for 9.24, hence that is the first version we consider
-    the feature available. (Ghostscript 9.24 has its own problems is blacklisted.)
-    """
-    return version() >= '9.24'
-
-
 def _gs_error_reported(stream) -> bool:
     match = re.search(r'error', stream, flags=re.IGNORECASE)
     return bool(match)
@@ -201,20 +186,9 @@ def generate_pdfa(
         ]
 
     strategy = 'LeaveColorUnchanged'
-    # Older versions of Ghostscript expect a leading slash in
-    # sColorConversionStrategy, newer ones should not have it. See Ghostscript
-    # git commit fe1c025d.
     gs_version = version()
-    strategy = ('/' + strategy) if gs_version < '9.19' else strategy
-
-    if gs_version == '9.23':
-        # 9.23: added JPEG passthrough as a new feature, but with a bug that
-        # incorrectly formats some images. Fixed as of 9.24. So we disable this
-        # feature for 9.23.
-        # https://bugs.ghostscript.com/show_bug.cgi?id=699216
-        compression_args.append('-dPassThroughJPEGImages=false')
-    elif gs_version == '9.56.0':
-        # 9.56.0 breaks our OCR...?
+    if gs_version == '9.56.0':
+        # 9.56.0 introduced a new rendering mode that breaks our OCR
         compression_args.append('-dNEWPDF=false')
 
     # nb no need to specify ProcessColorModel when ColorConversionStrategy

src/ocrmypdf/builtin_plugins/ghostscript.py

@@ -21,37 +21,19 @@ def check_options(options):
         program='gs',
         package='ghostscript',
         version_checker=ghostscript.version,
-        need_version='9.15',  # limited by Travis CI / Ubuntu 14.04 backports
+        need_version='9.50',  # Ubuntu 20.04's version
     )
     gs_version = ghostscript.version()
-    if gs_version in ('9.24', '9.51'):
+    if gs_version in ('9.51',):
         raise MissingDependencyError(
             f"Ghostscript {gs_version} contains serious regressions and is not "
             "supported. Please upgrade to a newer version, or downgrade to the "
             "previous version."
         )
 
-    # We have these constraints to check for.
-    # 1. Ghostscript < 9.20 mangles multibyte Unicode
-    # 2. hocr doesn't work on non-Latin languages (so don't select it)
-    is_latin = options.languages.issubset(HOCR_OK_LANGS)
-    if gs_version < '9.20' and options.output_type != 'pdf' and not is_latin:
-        # https://bugs.ghostscript.com/show_bug.cgi?id=696874
-        # Ghostscript < 9.20 fails to encode multibyte characters properly
-        log.warning(
-            f"The installed version of Ghostscript ({gs_version}) does not work "
-            "correctly with the OCR languages you specified. Use --output-type pdf or "
-            "upgrade to Ghostscript 9.20 or later to avoid this issue."
-        )
-
     if options.output_type == 'pdfa':
         options.output_type = 'pdfa-2'
 
-    if options.output_type == 'pdfa-3' and ghostscript.version() < '9.19':
-        raise MissingDependencyError(
-            "--output-type pdfa-3 requires Ghostscript 9.19 or later"
-        )
-
 
 @hookimpl
 def rasterize_pdf_page(

tests/plugins/gs_feature_elision.py

@@ -9,13 +9,13 @@ from ocrmypdf import hookimpl
 from ocrmypdf.builtin_plugins import ghostscript
 from ocrmypdf.subprocess import run_polling_stderr
 
-elision_warning = """GPL Ghostscript 9.20: Setting Overprint Mode to 1
+ELISION_WARNING = """GPL Ghostscript 9.50: Setting Overprint Mode to 1
 not permitted in PDF/A-2, overprint mode not set"""
 
 
 def run_append_stderr(*args, **kwargs):
     proc = run_polling_stderr(*args, **kwargs)
-    proc.stderr += '\n' + elision_warning + '\n'
+    proc.stderr += '\n' + ELISION_WARNING + '\n'
     return proc
 
 

tests/test_main.py

@@ -716,11 +716,9 @@ def test_compression_changed(ocrmypdf_exec, resources, image, compression, outpd
     if compression == "jpeg":
         assert pdfimage.enc == Encoding.jpeg
     else:
-        if ghostscript.jpeg_passthrough_available():
-            # Ghostscript 9.23 adds JPEG passthrough, which allows a JPEG to be
-            # copied without transcoding - so report
-            if image.endswith('jpg'):
-                assert pdfimage.enc == Encoding.jpeg
+        if image.endswith('jpg'):
+            # Ghostscript JPEG passthrough - no issue
+            assert pdfimage.enc == Encoding.jpeg
         else:
             assert pdfimage.enc not in (Encoding.jpeg, Encoding.jpeg2000)
 

tests/test_validation.py

@@ -48,22 +48,6 @@ def test_hocr_notlatin_warning(caplog):
     assert 'PDF renderer is known to cause' in caplog.text
 
 
-def test_old_ghostscript(caplog):
-    with patch('ocrmypdf._exec.ghostscript.version', return_value='9.19'), patch(
-        'ocrmypdf._exec.tesseract.get_languages', return_value={'eng', 'chi_sim'}
-    ):
-        vd.check_options(*make_opts_pm(language='chi_sim', output_type='pdfa'))
-        assert 'does not work correctly' in caplog.text
-
-    with patch('ocrmypdf._exec.ghostscript.version', return_value='9.18'):
-        with pytest.raises(MissingDependencyError):
-            vd.check_options(*make_opts_pm(output_type='pdfa-3'))
-
-    with patch('ocrmypdf._exec.ghostscript.version', return_value='9.24'):
-        with pytest.raises(MissingDependencyError):
-            vd.check_options(*make_opts_pm())
-
-
 def test_old_tesseract_error():
     with patch('ocrmypdf._exec.tesseract.version', return_value='4.00.00alpha'):
         with pytest.raises(MissingDependencyError):