I'm currently experimenting capabilities of converting files and compressing pictures, mainly jpg.
The language of my pdfcreator 3.3 version is set to french.
As a ratio I can't not enter a decimal number (like 0,5 or 0.5): there is an error message "number not converted" (in french : "le nombre 0.5 n'a pas pu être converti"). But It is accepted to enter 0, or 1, or 10, or 80...
So, does anyone know the available range of the jpg compression ratio ?
first let me point out, the setting you are referring to will influence only images inside of PDFs you create with PDFCreator; if you just want to compress jpgs (and still have a jpg as output), you first need to change the output format to jpeg, which will then give you different settings:
To answer your original question: The setting JPEG-manual seems to not be working properly in the current version. I looked at the code and it sets QFactor
"-dQFactor=M (float from 0.0 to 1.0) Adobe's QFactor quality scale, which you may use in place of JPEGQ above. The QFactor scale is used by PostScript's DCTEncode filter but is nearly unheard-of elsewhere."
(from Ghostscript docs)
The default setting used by PDFCreator is 0.66, but somehow it isn't possible to enter any decimal (as you pointed out); we will look into it.
For the current version 0 is best quality and anything above 20 will probably result in unusable image quality.
it is now fixed in production code and the update will be available soon, probably by tomorrow.
I made further experiments.
Concerning the JPG compression rate, it's possible to enter a pourcentage.
That is to say : you can't enter "0.54", but entering "54%" is accepted, and automatically changed into "0.54".
This remark could be usefull for your production code.