We call Corona (un)biased render engine, meaning that it offers both unbiased and biased rendering methods. The bias is however hard to notice, and most importantly it is introduced to make rendering more efficient and in turn faster, so normally there is no need to disable it. Additionally, in some cases using the "fully unbiased" settings may lead to noise and fireflies that might never go away, but if you want to try it, here is how:
- In Render Setup> Performance set both primary and secondary GI solvers to Path Tracing
- Set Max Sample Intensity to 0
- Make sure that Highlight clamping under Render Setup > System > Frame Buffer > Image Filter is set to 0
Additionally, if you want to get pure 32-bit output without any kind of "artistic" color mapping such as contrast or highlight compression, make sure that all your tone mapping settings (Post tab in Corona VFB or Render Setup > Scene > Tone Mapping) are set to defaults.