Hmm I don't know how to put this exactly... Let's imagine this: Using P5, I want to set a scene with several people (why not a public poolside, for example). I am aware that including too many people, even if they are dorks and posettes, will seriously kill my rendering speed, or even jam P5. Is there a workaround for that kind of problem ? I mean, except using some backdrop panels.

Render in sections and piece it together in Photoshop.

You can also pose your characters, export them as obj's and re-import the static obj's. They take up far less memory than a full character, and can stil be textured :o)

Render in pieces, starting with objects farthest from the camera and behind other objects, save as PSD or TIF so you have an alpha channel, then assemble in a paint program. Or render in pieces, starting farthest from the camera and behind other objects, Then use MenuDisplayPaste onto Background to create layers in Poser.

For 'background crowds' where close up details are not relivant then you can start as wyrwulf says "starting with objects farthest from the camera and behind other objects, save as PSD or TIF so you have an alpha channel" and then in your paint program create a Transparancy. Apply these to a flat plane to line up your crowd - very much the way Cyclorama has for trees/plants and what-not.

The problem with that approach is that it's hard to get convincing shadows. Shadows from the layer in front of a flat one will not fall 100% correct. In most cases it doesn't really matter, but the "imported object" doesn't suffer from that. On the other hand it is of course higher in polycount than a flat square :o)

Actually I prefer SamTherapy's method, sometimes I will have half a dozen or more PZ3s of the same scene each containing 'some' of the characters that will create the full scene once assembled in Photoshop. There is still a lot of planing involved where shadows are conserned. I sometimes use plain boxes, cones and what-nots as "stand-ins" to assist in cutting down the postwork or making sure the light doesn't get too strong where a missing character is in one of the 'parts of'. It does get kinda tricky sometimes trying to decide which characters to put into which part of the scene.... My example for this would be my "Beastiality" post in the gallery: 1 Mike2, 1 Naga, 1 Krysta, 1 Constanze, 2 P4Fems, 1 peacock, 1 salamander, 1 frog, 1 crow, 1 rabbit/P4cat, 3 butterflies, and a many props and clothing items; all rendered on a Win98 with only a PII and 256Meg of RAM. http://www.renderosity.com/viewed.ez?galleryid=129271

won't it be wiser to do the oppopsit ? i mean render the first plane and then the others, to cast the shadows of each foregroudn plane over the most backward ones , means one people in front will for sure cast a shadow on the one behind him if light is from front,ney ?

??? I assume you are refering to the 'Copy to Background' method? You would have to start from the rear since if you start from the front you would have those in the rear super imposed 'in front' of those in the front. And you would not be able to cast any shadows on each proceeding one at all unless you use a flat plane and then the shadows would tend to float in mid air. Using the method I described with mutiple planes you would catch some shadows but as ernyoka1 points out they will not be exact as if there were actual characters (or props of characters) there. You could get some shadows but they are cast off flat image planes.

Hi... I use the method of multiple PZ3s and this is one of the results...As for missing shadows you can allways paint them in Photoshop...

Attached Link: http://www.renderosity.com/viewed.ez?galleryid=662006&Start=1&Artist=Tyger%5Fpurr&ByArtist=Yes

You just need to be aware of where the shadows are and cut it up accordingly.

I did this image
http://www.renderosity.com/viewed.ez?galleryid=679353&Start=1&Artist=Tyger%5Fpurr&ByArtist=Yes

in multiple runs. I even changed the lighting to allow me to cut it up easier.

There are different methods for different needs.
You can cut them side to side and post work them together.
You can layer them back to front and post work them together.
You could even layer them from back to front and use the back image as a background image for the next closer layer. This is how i did the image linked above.

This image

http://www.renderosity.com/viewed.ez?galleryid=662006&Start=1&Artist=Tyger%5Fpurr&ByArtist=Yes

is the first one i layered and i explain where the layers are and how i put it together.

Thanks to all of you for these tips... I'll try them tomorrow I think, and see if I can make it right :) A question though to Ernokya: when exporting of the characters as obj, can you just retexture them back with their original texture within the materials room ?