Support Ghostscript 9.14's new color conversion engine (not portable)

The flag -dUseCIEColor is now deprecated, as it invokes the old engine
which introduces color errors. The new engine requires a PDF/A file
header with hardcoded location of a ICC profile to use, now included in
the project. Portable iterations should generate a PDFA_def.ps based on
the target system; for now OS X with homebrew is presumed.

I have selected sRGB since scanners tend to capture RGB and printing
is not a major consideration for PDF/A.

Also note all file paths given to gs must be absolute. May its creators
be forever haunted for their failure to document this unexpected quirk.

OCRmyPDF.sh

@@ -278,9 +278,10 @@ ret_code="$?"
 
 # concatenate all pages and convert the pdf file to match PDF/A format
 [ $VERBOSITY -ge $LOG_DEBUG ] && echo "Output file: Concatenating all pages to the final PDF/A file" 
-! gs -dQUIET -dPDFA -dBATCH -dNOPAUSE -dUseCIEColor \
-	-sProcessColorModel=DeviceCMYK -sDEVICE=pdfwrite -sPDFACompatibilityPolicy=2 \
-	-sOutputFile="$FILE_OUTPUT_PDFA" "${TMP_FLD}/"*ocred*.pdf 1> /dev/null 2> /dev/null \
+! gs -dQUIET -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sColorConversionStrategy=/RGB \
+	-sProcessColorModel=DeviceRGB -dPDFA -sPDFACompatibilityPolicy=2 \
+	-sOutputICCProfile=srgb.icc \
+	-sOutputFile="$FILE_OUTPUT_PDFA" "$(pwd)/PDFA_def.ps" "${TMP_FLD}/"*ocred*.pdf \
 	&& echo "Could not concatenate all pages to the final PDF/A file. Exiting..." && exit $EXIT_OTHER_ERROR
 
 # validate generated pdf file (compliance to PDF/A)

PDFA_def.ps

@@ -0,0 +1,40 @@
+%!
+% This is a sample prefix file for creating a PDF/A document.
+% Feel free to modify entries marked with "Customize".
+% This assumes an ICC profile to reside in the file (ISO Coated sb.icc),
+% unless the user modifies the corresponding line below.
+
+% Define entries in the document Info dictionary :
+/ICCProfile (/usr/local/share/ghostscript/iccprofiles/srgb.icc) % Customise
+def
+
+[ /Title (PDF)       % Customise
+  /DOCINFO pdfmark
+
+% Define an ICC profile :
+
+[/_objdef {icc_PDFA} /type /stream /OBJ pdfmark
+[{icc_PDFA}
+<<
+  /N currentpagedevice /ProcessColorModel known {
+    currentpagedevice /ProcessColorModel get dup /DeviceGray eq
+    {pop 1} {
+      /DeviceRGB eq
+      {3}{4} ifelse
+    } ifelse
+  } {
+    (ERROR, unable to determine ProcessColorModel) == flush
+  } ifelse
+>> /PUT pdfmark
+[{icc_PDFA} ICCProfile (r) file /PUT pdfmark
+
+% Define the output intent dictionary :
+
+[/_objdef {OutputIntent_PDFA} /type /dict /OBJ pdfmark
+[{OutputIntent_PDFA} <<
+  /Type /OutputIntent             % Must be so (the standard requires).
+  /S /GTS_PDFA1                   % Must be so (the standard requires).
+  /DestOutputProfile {icc_PDFA}            % Must be so (see above).
+  /OutputConditionIdentifier (sRGB)      % Customize
+>> /PUT pdfmark
+[{Catalog} <</OutputIntents [ {OutputIntent_PDFA} ]>> /PUT pdfmark