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https://issues.apache.org/jira/browse/PDFBOX-4137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16383298#comment-16383298
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Tilman Hausherr commented on PDFBOX-4137:
-----------------------------------------
We may need an [ICLA|https://www.apache.org/licenses/icla.pdf] for this patch
https://www.apache.org/licenses/#clas
> Allow subsampled/downscaled rendering of images, and rendering subimages
> -------------------------------------------------------------------------
>
> Key: PDFBOX-4137
> URL: https://issues.apache.org/jira/browse/PDFBOX-4137
> Project: PDFBox
> Issue Type: Improvement
> Components: Rendering
> Affects Versions: 2.0.8
> Reporter: Itai Shaked
> Priority: Minor
> Attachments: 0001-Image-render-subsample.patch,
> image_rendering_subsampling_hack.patch
>
>
> Suggested/contributed change to allow subsampling of images and rendering
> sub-regions of images.
> The need arises from having very large images which are highly compressed
> (usually JPEG or JBIG2). The current implementation decodes the entire image
> into memory at full resolution, even if rendering is done at a much lower
> resolution.
> Since the change required augmenting the way Filters work (to allow
> partial/subsampled decoding), it also includes a partial fix for PDFBOX-3340.
>
>
> This change introduces "DecodeOptions" which are currently only applicable
> for images. They include requesting only metadata (for PDImageXObject's
> repair method), subsampling and sub-region (similar to
> javax.imagio.ImageReadParam).
> Since not all filters can or do honor (use) the options, the DecodeOptions
> class contains a flag. Filters that honor the options (subsample / decode
> only requested region) set it to true. If the flag is false, the subsampling
> or cropping should be done after decoding, to ensure consistency.
> PageDrawer was modified so it uses subsampling based on the ratio of the
> desired output to the original image.
>
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