Hi Again, To get the ball rolling, attached is proposed patch to src/base/pdf-stm-f-pred.c.
The crux of this patch is that encoded PNG predictor tags should be in the
range 0..4, as specified in
section 6 of RFC 2083 Portable Network Graphics Specification, not 10..14.
There's also a couple of minor secondary fixes to (a) keep PNG, TIFF and
NONE modes distinct and (b) ensure also PNG prediction arithmetic is
unsigned (pdf_uchar_t, rather than pdf_char_t)..
I haven't worked out how to drive the test sub-system yet, but the
following program demonstrates some of the expected differences:
include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "pdf.h"
void main() {
pdf_error_t *error = NULL;
pdf_char_t* buf = "\100\101\102"
"\120\120\120";
pdf_size_t buflen = strlen(buf);
pdf_stm_t* stm = pdf_stm_mem_new(buf, buflen, 0, PDF_STM_READ, &error);
pdf_hash_t* hash = pdf_hash_new(&error);
pdf_hash_add_size(hash, "Predictor", 11, &error);
pdf_hash_add_size(hash, "BitsPerComponent", 8, &error);
pdf_hash_add_size(hash, "Colors", 3, &error);
pdf_hash_add_size(hash, "Columns", 1, &error);
pdf_stm_install_filter(stm, PDF_STM_FILTER_PRED_ENC, hash, &error);
pdf_char_t outbuf[100];
pdf_size_t read_bytes;
pdf_stm_read(stm, outbuf, sizeof(outbuf), &read_bytes, &error);
fprintf(stdout, "read bytes: %ld", read_bytes);
/* dump the output buffer */
for (int i = 0; i < read_bytes; i++) {
char* fmt = i%4 ? " %d" : "\n[%d]";
fprintf(stdout, fmt, (int) outbuf[i]);
}
fprintf(stdout, "\n");
if (error) {
fprintf(stderr, "error: %s", pdf_error_get_message(error));
exit(1);
}
exit(0);
}
This program is encoding with the PNG 'sub' filter (/Predictor 11).
Before applying the patch it produces
[11] 64 1 1
[11] 80 0 0
After applying this patch:
[1] 64 1 1
[1] 80 0 0
I'm hoping that someone on the mailing list has time to dust-off
gnupdf and look at the attached patch.
Feedback welcome.
Regards,
David
On Tue, Mar 29, 2016 at 3:46 PM, David Warring <david.warr...@gmail.com>
wrote:
> Hi All,
> As a newcomer to gnupdf, I've gone to the trouble of downloading the
> project from the bazaar repo at http://bzr.savannah.gnu.org/r/pdf and
> building and installing (still works).
>
> At this stage, I'm most interested in filters and streams. I'm looking for
> a suitable stream/filter/encryption backend for Perl 6 module which is
> under development (https://github.com/p6-pdf/perl6-PDF-Tools).
>
> I realize that this project has been inactive for some-time, but it
> seems to me that the low level stuff that I'm interested in, such as
> filters is working or close working, but may need some bug fixes and
> general support to get it across the line.
>
> Is anyone interested in picking up bug fixing and general support for
> gnupdf?
>
> Regards,
> David Warring
>
gnupdf-predictor-patch-dw.bzr
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