[jira] [Created] (PDFBOX-4137) Allow subsampled/downscaled rendering of images, and rendering subimages

["Itai Shaked (JIRA)" <ji...@apache.org>]

Itai Shaked created PDFBOX-4137:
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             Summary: 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
         Attachments: 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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