[PDFBOX-4137] Allow subsampled/downscaled rendering of images, and rendering subimages

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.0.8
• Fix Version/s: 2.0.9, 3.0.0 PDFBox
• Component/s: Rendering
• Flags: Patch
• Assignee: Tilman Hausherr
• Reporter: Itai Shaked
• Created: 01/Mar/18 21:05
• Updated: 28/Mar/18 16:33
• Resolved: 08/Mar/18 19:06

Description

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. 

 

Issue Links

• is related to: PDFBOX-4169 PDFPrintable has subsampling but it can not be used
• links to: PDF with huge embedded image is displayed as a blank page #6741