Memory usage too high
Note: This article applies to pre-1.4 versions of Corona Renderer only!
Rendering high-resolution images can sometimes be heavy on memory and even lead to system freezes or crashes. To reduce memory footprint, you can try following:
Reduce Internal res to 1 (This applies to pre-1.4 versions of Corona only. Internal resolution setting was removed in newer versions.)
You can find it in Render Setup > System > Frame Buffer > Image filter
Internally multiplies the rendered resolution by a given factor. Using value higher than 1 increases memory consumption significantly, but when used, it is possible to antialias very bright edges of lights. Use default value of 1 unless light edges antialiasing is needed, in that case set it to 2.
See: I can see jagged edges!
Render Non-shading elements separately
Each element in Corona Renderer, which is computed during rendering, consumes memory. More elements = more memory usage. This rule is especially significant while rendering high-resolution images.
To reduce memory footprint while rendering high-resolution images, you can simply render all non-shading elements (masks, normal maps, zdepth, etc.) in separate rendering session using the "Render Only Elements" function.
You can find it in Render Setup > Scene > General Settings > Render only elements button
For a list of all available render elements, see: What render elements are there?
If you are using displacement, in Render Setup > Performance under "displacement" section set displacement's "screen size" to a higher value
Other possible causes of excessive RAM usage include rendering large amounts of objects or detailed mesh - in such case it is advised to optimize the scene.
See also: I am getting a sudden rise in RAM usage!