Why does the PDFNet Optimizer create such large JPEGs?

[Aaron Gravesdale]

Q:

I've optimized a file both in Acrobat and PDFNet.  In each, I set the options to prefer JPEG compression.  (In PDFNet, this is done with Optimizer.ImageSettings.SetCompressionMode(e_jpeg).)  I set the PDFNet compression level to 9 (using Optimizer.ImageSettings.SetQuality()) and the Acrobat compression level to "Medium".  The PDFNet output is much larger.  Why?

A:

After analyzing the quality of JPEGs output from PDFNet and Acrobat at different levels, it seems that Acrobat's "Medium" level approximates PDFNet's quality level "3".  Here is a table of the correlations we've found between settings in each:

Acrobat ..... PDFNet
Minimum ..... 1
Low ......... 2
Medium ...... 3
High ........ 4-6
Maximum ..... 7-9

At these settings, Acrobat and PDFNet also create similarly-sized JPEGs.