EDIT; Ha! Paolo beat me to it! ...I probably rambled on a bit! `¬)

The default rendered image you end up with is .PNG. This is not related to any images used in the original scene for either maps or backdrops. I assume for back drops you mean setting an image onto a plane within your daz scene before you render... http://fav.me/d4aky2i You can either add the image to the plane in daz studio, or you can load the image onto the item in the Reality interface as indicated here...

I hope it is not too confusing in that I am illustrating with an older version of DazStudio and Reality?

...as far as render size goes, I generally render the same size resolution of my pc screen which is in my case 1920 x 1200 pixels. That means it will fill my whole screen when viewd full size. I cannot see much reson to render bigger than this, as otherwise to view full size on screen means having to scroll around the window!

On the other hand, if you wanted to print out your render poster sized, you might want to render an image with higher resolution but this will depend on the printer resolution. This is where your 'ppi' comes in. It gets a bit complecated, as it can take several 'dots' on a printed image to resolve a single pixel colour...

ppi is a bit redundant when it comes to a monitor, as most 'standard' monitors these days (rather than top rate graphics monitor which would/could have far higher resolution), are 1920 x 1080 for widescreen (my screen is 16:10 rather than 16:9 - the ratio of the width to the height). Depending on the physical size of your monitor will determine how many pixels per inch you will have. A 1920 x 1080 pixels on a 28" monitor will be far less ppi than on a 18" monitor...

This is just my opinion, I'm sure others may be able to give good reasons to render at other sizes...

Incidently, I would not render full size you want until you are happy with all your settings. I generally start test renders at about 50% size, as I can see the results faster. Once most of the tweaks are done, I may go to 75%, and when I am happy with the whole scen, I will then go to a full 100% size render. That way, you can see how your scene / image progresses as you add or change items. Until you are very familiar, it is probably not a good idea to fill your scene and set it all up before doing a test render. I will start a scene and test render each item I add or change. Sometimes I will set up a completly seperate scen from my original if I want to test some settings on only one object. Once it looks right, I can then add it to my main scene knowing the settings are right - rather than rendering lots of other things in the scene that I'm not interested in at that point.

At the end of the day, if your target 'audiance' are viewing on a monitor, then its probably best to match the 'avarage' monitor size, and if your target is to print out posters, then you will likely need to render larger to take into account the requirements of the poster size and the capabilities of the printing process used. Some usefull info here if you really want to delve into it... (personally it just made my head hurt! `¬)

 http://en.wikipedia.org/wiki/Dots_per_inch http://en.wikipedia.org/wiki/Pixel_density

 

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