You can process both .jpg and .png files in the same batch job.
Dbblast will use the specified image save quality (see Settings Menu).
Basically, for .jpg files the save quality will determine the
image quality and file compression level, while for .png files
the save quality determines compression level only.
One caveat: dbblast looses exif data when it saves .png files.
At present the exiv2 library only has read support for .png exif
data. In the meantime, you can use Phil Harvey's ExifTool
to copy exif data to the processed .png images.
Last time I checked there was a standalone Windows executable, so,
you no longer need to install Perl to run ExifTool on windows.
As an example, the following commands will copy all exif data
from infile.png to outfile.png:
exiftool -all= outfile.png
exiftool -TagsFromFile infile.png outfile.png