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3Deoskill wrote: Why does the image manager need such a long preparation time for huge scenes, whereas the CentiLeo IPR needs zero preparation time. Why can't this technique also be used for rendering in the Picture Manager? I don't really understand. Or why can't you perhaps offer a similar mode similar to that in the CentiLeo IPR. Sorry if this is a stupid question

The Picture Viewer render is the render and scene preparation made by Cinema 4D. It's needed to copy and evaluate the entire scene as it is including all objects, expressions, tags and etc. While in CentiLeo IPR we also do this, but very often it's done over time while we manage the scene. Also for IPR we usually change camera, materials and light sources and see immediate result. But for PV we need to re-evaluate everything from scratch for each frame.

You may read the article about Final render mode in CentiLeo IPR for interest:
https://centileo.com/docs/index.php?COURSE_ID=3&LESSON_ID=70&LESSON_PATH=17.70
https://centileo.com/docs/index.php?COURSE_ID=3&LESSON_ID=39&LESSON_PATH=17.39#fingeo