Add option to resample bitmap graphics when exporting as PDF

This affects Inkscape 0.48.3.1 r9886 (Jan 29 2013), part of Ubuntu 12.04 LTS.

I have created an Inkscape document with a page size of 10 cm x 10 cm. I have then put four raster graphics into the document, all quite highly resolved (PNG files with about 1500x1500 pixels). Almost no more additional objects, just a few words of text. I have then used the "Save copy as" function in order to save a PDF file with the following settings:

- PDF 1.4 compat
- convert texts to paths
- resolution for rasterization: 300 or 100 or 10 dpi
- export area is page

I have saved the document and the resulting PDF file had a size of 3.2 MB, *independent* of the rasterization DPI setting. Is that expected behavior? I wanted Inkscape to downscale the bitmaps, according to the dpi setting.

Inkscape has to process the bitmaps anyway (for saving the raster image to the PDF in a certain encoding), so why does Inkscape not downscale the source material according to the DPI setting in the PDF dialogue?

Current workaround: I have further post-processed the 3.2 MB PDF file with GhostScript:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dDownsampleColorImages=true -dColorImageResolution=300 -dNOPAUSE -dBATCH -sOutputFile=out.pdf in.pdf

which yielded a 150 kB PDF file.

Maybe this is not a bug, but in any case I would like to know what the intendend behavior is and why, and which method the Inkscape authors recommend for controlling the raster image resolution in a PDF file.