I have a potential client asking questions about Bloom’s PDF quality. The main question seems to be something like, if you use a 300 dpi image in a Bloom book, will you still get 300 dpi quality in the resulting PDF. I know that Bloom does PDF compression in the PDF creation process. What techniques are used to achieve the compression? And how does this affect the resulting PDF quality compared to the original elements used?
The PDF files produced directly by the Geckofx/Mozilla/Firefox printing code that we use can be really huge depending on the images in the original file. (Apparently images are laid out in raw bitmap fashion at their original resolution.) For desktop publishing (what you normally get initially with RGB color), images are reduced if necessary to 600 dpi (1200dpi if true black and white). For printshop output (choosing CMYK color when saving the file), images may be reduced to 300dpi, but no further.
Bloom uses the ghostscript program to process the PDF files for both compression and CMYK color conversion. If the original images were at 300dpi as laid out in Bloom, they should retain their quality in the PDF printing process.
I could provide the command line arguments that we pass to ghostscript, but that’s a technical level that even I can’t claim to understand any longer this many years after I wrote the code. I’d have to go back to reading the ghostscript manual…
That’s really helpful. Thanks, Steve. No more needed.