Starbright Illustrations (blog)

By The Illustrator 　http://starbrightillustrations.com/blog/2010/08/27/quick-and-dirty-partial-render-with-blender-2-5/

spaceship detail

After a little bit of searching I’ve found a way to dramatically speed up my test renders. I’ve been greebling the surface of my spaceship lately, and each greeble is only a tiny part of the hull, some bigger (engine hatches, thrusters) some smaller (antenna, door handles), but to take a look at each new greeble I’ve been rendering the entire spaceship each time.

Unfortunately this can take almost an hour if my knackered old computer is in a bad mood, or if there is a lot of glass in the shot.

This page  Doc:2.4/Books/Essential Blender/13.3.Render Settings: Discussion – BlenderWiki. however has a great solution. I can simply select the little bit of the spaceship that I’m interested in (he bit with the new greeble) by drawing a box around it while in a camera view with “shift B”. Then only that small part of the spaceship will be rendered. You have to enable this function first by clicking the border button in Blender’s rendering control panel.

Here is the spaceship view that I would normally render, as you can see the camera is seeing the entire spaceship.

as the camera sees the spaceship

The 3D window view gives a good idea of how a feature will render, but just to be sure it’s always nice to have the option of creating a render and seeing the spaceship exactly as it will appear.
To do this quickly – in just three or four minutes, even on my rubbish old computer – “shift B” and select the just the bit you need to take a look at.

Blender still creates an image of the full size render, but most of it is blacked out. Only the part you selected has the actual coloured pixels of the finished render in.

most of the render is blacked out

As the time it takes to render each of these pixels can sometimes be measured in seconds, and there are thousands of them, this is obviously a huge advantage, especially if all you want is a quick look at just one little detail.