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From "Emmeran Seehuber (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PDFBOX-4184) [PATCH]: Support simple lossless compression of 16 bit RGB images
Date Tue, 15 May 2018 11:23:00 GMT

    [ https://issues.apache.org/jira/browse/PDFBOX-4184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16475681#comment-16475681
] 

Emmeran Seehuber commented on PDFBOX-4184:
------------------------------------------

I did a batch test using the govdocs zips 001 - 057 (I downloaded them over night) and found
another bug in the PNG Average... how hard can it be to type such a simple formula?! Now all
seems to be fine.

[^lossless_predictor_based_imageencoding_v5.patch]

I've added the test image (032.zip/163.jpg) and the matching test. I also included the tool
you built in the patch and extended it to allow using a directory with downloaded files for
the test. 

> [PATCH]: Support simple lossless compression of 16 bit RGB images
> -----------------------------------------------------------------
>
>                 Key: PDFBOX-4184
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-4184
>             Project: PDFBox
>          Issue Type: Improvement
>          Components: Writing
>    Affects Versions: 2.0.9
>            Reporter: Emmeran Seehuber
>            Priority: Minor
>             Fix For: 2.0.10, 3.0.0 PDFBox
>
>         Attachments: LoadGovdocs.java, lossless_predictor_based_imageencoding.patch,
lossless_predictor_based_imageencoding_v2.patch, lossless_predictor_based_imageencoding_v3.patch,
lossless_predictor_based_imageencoding_v4.patch, lossless_predictor_based_imageencoding_v5.patch,
pdfbox_support_16bit_image_write.patch, png16-arrow-bad-no-smask.pdf, png16-arrow-bad.pdf,
png16-arrow-good-no-mask.pdf, png16-arrow-good.pdf
>
>
> The attached patch add support to write 16 bit per component images correctly. I've integrated
a test for this here: [https://github.com/rototor/pdfbox-graphics2d/commit/8bf089cb74945bd4f0f15054754f51dd5b361fe9]
> It only supports 16-Bit TYPE_CUSTOM with DataType == USHORT images - but this is what
you usually get when you read a 16 bit PNG file.
> This would also fix [https://github.com/danfickle/openhtmltopdf/issues/173].
> The patch is against 2.0.9, but should apply to 3.0.0 too.
> There is still some room for improvements when writing lossless images, as the images
are currently not efficiently encoded. I.e. you could use PNG encodings to get a better compression.
(By adding a COSName.DECODE_PARMS with a COSName.PREDICTOR == 15 and encoding the images
as PNG). But this is something for a later patch. It would also need another API, as there
is a tradeoff speed vs compression ratio. 



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