Add sanitize mode for stripping invisible text

OCR processes typically produce text objects with text render mode 3, so
this option allows stripping OCR layers for recreating them. This can
also simplify documents for print processing without visual impact.

Author: jsonn

include/mupdf/pdf/document.h

@@ -763,6 +763,7 @@ typedef struct
 	int do_use_objstms; /* Use objstms if possible */
 	int compression_effort; /* 0 for default. 100 = max, 1 = min. */
 	int do_labels; /* Add labels to each object showing how it can be reached from the Root. */
+	int do_strip_invisible_text; /* Strip invisible text (text render mode 3). */
 } pdf_write_options;
 
 FZ_DATA extern const pdf_write_options pdf_default_write_options;

include/mupdf/pdf/interpret.h

@@ -362,6 +362,7 @@ typedef struct
 	int (*text_filter)(fz_context *ctx, void *opaque, int *ucsbuf, int ucslen, fz_matrix trm, fz_matrix ctm, fz_rect bbox);
 	void (*after_text_object)(fz_context *ctx, void *opaque, pdf_document *doc, pdf_processor *chain, fz_matrix ctm);
 	int (*culler)(fz_context *ctx, void *opaque, fz_rect bbox, fz_cull_type type);
+	int strip_invisible_text;
 }
 pdf_sanitize_filter_options;
 

source/pdf/pdf-op-filter.c

@@ -635,7 +635,11 @@ filter_show_char(fz_context *ctx, pdf_sanitize_processor *p, int cid, int *unico
 	}
 	*unicode = ucsbuf[0];
 
-	if (p->options->text_filter || p->options->culler)
+	if (p->options->strip_invisible_text && gstate->pending.text.render == 3)
+	{
+		remove = 1;
+	}
+	else if (p->options->text_filter || p->options->culler)
 	{
 		fz_matrix ctm;
 		fz_rect bbox;

source/pdf/pdf-write.c

@@ -1721,7 +1721,7 @@ static void complete_signatures(fz_context *ctx, pdf_document *doc, pdf_write_st
 	}
 }
 
-static void clean_content_streams(fz_context *ctx, pdf_document *doc, int sanitize, int ascii, int newlines)
+static void clean_content_streams(fz_context *ctx, pdf_document *doc, int sanitize, int ascii, int newlines, int strip_invisible_text)
 {
 	int n = pdf_count_pages(ctx, doc);
 	int i;
@@ -1733,7 +1733,9 @@ static void clean_content_streams(fz_context *ctx, pdf_document *doc, int saniti
 	options.recurse = 1;
 	options.ascii = ascii;
 	options.newlines = newlines;
-	options.filters = sanitize ? list : NULL;
+	options.filters = sanitize || strip_invisible_text ? list : NULL;
+	if (strip_invisible_text)
+		sopts.strip_invisible_text = 1;
 	list[0].filter = pdf_new_sanitize_filter;
 	list[0].options = &sopts;
 
@@ -1916,6 +1918,8 @@ pdf_parse_write_options(fz_context *ctx, pdf_write_options *opts, const char *ar
 		opts->do_clean = fz_option_eq(val, "yes");
 	if (fz_has_option(ctx, args, "sanitize", &val))
 		opts->do_sanitize = fz_option_eq(val, "yes");
+	if (fz_has_option(ctx, args, "strip-invisible-text", &val))
+		opts->do_strip_invisible_text = fz_option_eq(val, "yes");
 	if (fz_has_option(ctx, args, "incremental", &val))
 		opts->do_incremental = fz_option_eq(val, "yes");
 	if (fz_has_option(ctx, args, "objstms", &val))
@@ -1990,12 +1994,12 @@ prepare_for_save(fz_context *ctx, pdf_document *doc, const pdf_write_options *in
 		fz_throw(ctx, FZ_ERROR_ARGUMENT, "annotations need resynthesis before saving");
 
 	/* Rewrite (and possibly sanitize) the operator streams */
-	if (in_opts->do_clean || in_opts->do_sanitize)
+	if (in_opts->do_clean || in_opts->do_sanitize || in_opts->do_strip_invisible_text)
 	{
 		pdf_begin_operation(ctx, doc, "Clean content streams");
 		fz_try(ctx)
 		{
-			clean_content_streams(ctx, doc, in_opts->do_sanitize, in_opts->do_ascii, in_opts->do_pretty);
+			clean_content_streams(ctx, doc, in_opts->do_sanitize, in_opts->do_ascii, in_opts->do_pretty, in_opts->do_strip_invisible_text);
 			pdf_end_operation(ctx, doc);
 		}
 		fz_catch(ctx)
@@ -2722,6 +2726,7 @@ void pdf_write_document(fz_context *ctx, pdf_document *doc, fz_output *out, cons
 			in_opts->do_linear ||
 			in_opts->do_clean ||
 			in_opts->do_sanitize ||
+			in_opts->do_strip_invisible_text ||
 			in_opts->do_appearance ||
 			in_opts->do_encrypt != PDF_ENCRYPT_KEEP)
 			fz_throw(ctx, FZ_ERROR_ARGUMENT, "Can't use these options when snapshotting!");
@@ -2864,6 +2869,8 @@ pdf_format_write_options(fz_context *ctx, char *buffer, size_t buffer_len, const
 		ADD_OPT("linearize=yes");
 	if (opts->do_clean)
 		ADD_OPT("clean=yes");
+	if (opts->do_strip_invisible_text)
+		ADD_OPT("strip-invisible-text=yes");
 	if (opts->do_sanitize)
 		ADD_OPT("sanitize=yes");
 	if (opts->do_incremental)

source/tools/pdfclean.c

@@ -61,6 +61,7 @@ static int usage(void)
 		"\t-i\tcompress image streams\n"
 		"\t-c\tclean content streams\n"
 		"\t-s\tsanitize content streams\n"
+		"\t-I\tstrip invisible text\n"
 		"\t-t\tcompact object syntax\n"
 		"\t-tt\tindented object syntax\n"
 		"\t-L\twrite object labels\n"
@@ -133,7 +134,7 @@ int pdfclean_main(int argc, char **argv)
 	opts.write = pdf_default_write_options;
 	opts.write.dont_regenerate_id = 1;
 
-	while ((c = fz_getopt_long(argc, argv, "ade:fgilmp:stczDAE:LO:U:P:SZ", longopts)) != -1)
+	while ((c = fz_getopt_long(argc, argv, "ade:fgilmp:stczDAE:ILO:U:P:SZ", longopts)) != -1)
 	{
 		switch (c)
 		{
@@ -149,6 +150,7 @@ int pdfclean_main(int argc, char **argv)
 		case 'l': opts.write.do_linear += 1; break;
 		case 'c': opts.write.do_clean += 1; break;
 		case 's': opts.write.do_sanitize += 1; break;
+		case 'I': opts.write.do_strip_invisible_text += 1; break;
 		case 't': pretty = (pretty < 0) ? 0 : 1; break;
 		case 'A': opts.write.do_appearance += 1; break;
 		case 'L': opts.write.do_labels = 1; break;