Re: [pdf-devel] Bugfix in prediction filter

[Georg Gottleuber]

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Hello,

I made another patch version for the prediction filter:

I have done some more bug fixes:
* PNG predictor filters processed streams byte
after byte. This is wrong, because the corresponding bytes per pixel
have to be processed (1st byte of pixel x with 1st byte of pixel x+1,
2nd ... with 2nd ...,  and so on). I introduced a new state variable
"bpp" (bits per pixel) and corrected all PNG predictors like they are
described in PNG RFC-2083.
* In the decoder it can happen that there is still something in the
input buffer but output is full. I think what I have overseen this
because it only happens if multiple filters are connected (I have not
tested predictor filter with another filter before). So I added the
same main loop condition as in the encoder:
+  while (!pdf_buffer_eob_p (in) && !pdf_buffer_full_p (out));
+
+  if (pdf_buffer_full_p (out) && !pdf_buffer_eob_p (in))
+    return PDF_STM_FILTER_APPLY_STATUS_NO_OUTPUT;
* It was possible to jump from PNG to TIFF prediction in the same
image decoding call. I caught this and decoding now fails with an
error message.

And some refactoring:
* changed all (pdf_char_t*)  to (pdf_uchar_t*)
* added a paeth predictor function, to beautify enc/decode_row_paeth

I have tested these changes with following pictures (PDFs produced by
pdflatex and tested against mupdfs pdfshow):
* 8x8 Pixel, 1 color/component,   4 bits per component
* 8x8 Pixel, 1 colors/components, 8 bits per component
* 8x8 Pixel, 3 colors/components, 24 bits per component
* 32x32 Pixel, 3 colors/components, 24 bits per component
* 1555x633 Pixel, 3 colors/components, 24 bits per component
(all encoded with gimp, which uses optimum prediction and thus uses
different predictors; in fact all but row_up, which is the only one I
didn't change because it works already on corresponding pixels)

Please merge the patch.

Regards,
Georg

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pdf-stm-f-pred-v2.patch
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