Blender 3D: Noob to Pro/OSA

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OSA stands for oversampling, also known as anti-aliasing. If you look at the rendering below, you'll find that the one has a rugged edge. It looks like small steps! To stop this, Blender uses OSA to prevent "jagged edges" or "aliasing" as it's called.

Oversampling settings in render tab.

This occurs when you have a diagonal change of colour, which results in rough edges. Remember drawing a diagonal line in Paint? To overcome this hindrance of square pixels, a technique called anti-aliasing or "oversampling" is used. It blends the colours around the rough edge to create a smooth, but defined edge. One way of doing this is to by creating the image twice as large, then scaling it down - oversampling. Blender can do this for you if you select an OSA rate. Remember this will take much longer, but results in better renders, so use this for the final product, not while testing. In some cases the scene can seem blurred due to oversampled textures; try changing the OSA setting, or oversampling yourself.

Here's a quick illustration of how OSA changes a render (look at the edges):

The image on the left has no OSA. The one on the right has 16x (the maximum amount allowed by Blender).

OSA settings can be manipulated in from the Render Settings panel.