This is the basic NConvert code to combine JPEGs into a multipage PDF file while maintaining the original image Q value:
Code: Select all
NConvert -out pdf -multi -use_org_quality -c 5 -o Test.pdf *.jpg
This is the basic code to set a Q value of 85, the value shown for your source::
Code: Select all
NConvert -out pdf -multi -q 85 -c 5 -o Test.pdf *.jpg
The inclusion of the following subsampling term may slightly improve the output image quality but I haven't tested that, if you try it I would be interested to know::
Testing quickly, there is little or no evident loss of image quality for the JPEGs you uploaded when the Q value is reduced to 60 or even 50, with a resulting significant reduction in the output file size:
Q=85 - 2.62 MB
Q=70 - 2.01 MB
Q=60 - 1.44 MB
Q=50 - 1.36 MB
If you have a PDF viewer that can display multiple files in tabs, such as Adobe Acrobat (the basic free version, whatever it is called now) it is very easy to compare the quality of alternative output versions, zoom in equally on each for a closer look.
Beyond that, it looks as if your images might benefit with some preprocessing, a separate topic and probably one for someone else, I notice a slight blue-ish tint, and they might respond to slight sharpening, for example.
Given reasonable quality images of typical text rather than primarily photographic pages, I could test the effect of using Adobe Clearscan, which in favourable circumstances can be very effective in reducing file size, but which unfortunately is becoming less accessible as I believe it is now only included in the premium Acrobat Pro version.