Maybe my problem has already been solved, but I really need your help please: I cannot find good parameters to avoid this visible pixalisation on the image. Could you help one newbie once more please ?

It looks to me as if you have the bump strength on far too high. Try reducing that and see how it comes out. If it's not that, or if there is no bump map, check the size of the map you're using. It may simply not be high enough resolution for close-up work.

Thanks Karen1573 I tried that but the problem is still there. Here are Firefly render settings: Production quality Use displacement map disabled Raytracing off Cast shadows enabled Smooth polygons enabled Remove backfacing polygons enabled Use texture filtering enabled and set to 1.0 (min shading 1.000 - Max texture resolution to 4096) Pixels samples to 6 post filtering to 1 and type "box" So, textures resolution are 4096x4096 (body map). The problem disappears when texture filtering value is disabled but hairs and eyelashes are low quality). I don't know what to do.

Next, I also don't like using texture filtering, thats just me though.

Finally are you setting the texture in the materials room or are you using automatic settings. If the settings are automatic they will probably be plugged into the gradient bump node (In the material room) Personally, I like to take a Hi Res texture plug it into the bump node (about six or seven lines above the gradient bump node and then set the texture strength(located to the left of the node icon)to a very low setting. I find .005 to .015 to be about the max for realistic skin textures. (I use .01 to .015 only on the lips and tongue for extreme close ups.
Give that a try and let me know.

BTW this pic was one I used to test a throat texture map I'm working on, but it also uses the settings I described above.

Just realized that I left out few details. First I ASSuME you are using a texture that includes bump maps(otherwise you probably wouldn't have this problem. So go to Materials room and make sure the bump is plugged into a node (either gradient bump or as described in previous post) Second, if you are using bumps then you probably want to have diplacement maps enabled. And finally try turning on raytracing also. Try that first, if you want to refine it and if you have a really good computer with lots of resources you can improve the look of most textures by turning up the value on the minimum shading rate (if your computer can handle pixel samples setting of 6 you could probably turn up the shading rate above 1 also.)