XnView Software

Thanks, you are doing a great job of explaining but maybe I am using the wrong version of software.
Version 1.65-x64 (Aug20,2014) Libformat version 6.60)

When I add the Posterize action I do no t get a slider but I get a drop down menu with choices of color (4, 8, 16, etc.)
No slider.

However, I ...

Here are two images from a scan. (Before.tiff is the original scan) Using another conversion program the "Before" was converted with an adjustable threshold setting to arrive at the high contract version "after".
The program also gave an option to save as a low res gif. What was before a 258 KB file ...

I am new to this forum but good at following instructions. How do I upload. Do I need to leave the forum and go to an upload page on the site?

Thanks, it does answer the question about the "average" option. But that is just one of the many actions that can be added. I understand several actions such as "resize" and "rotate" but my post also asked if there is a manual or reference document that explains the other actions available.

In a ...

I guess MP as I am running it on a Mac.

In the "filters" section under "average" there are options in a drop down menu for 3x3, 5x5, etc. Whit is this averaging?
Is there some place I can find a description about the various actions?

I am new to this forum having just discovered this program. Have used Lemke's Graphic Converter but find this has features his apparently does not.
Is there a manual or guide somewhere? I don't understand some of the terms used, such as the numeric choices in action "filter size".

I need to ...