This is still a big problem for us. We are currently working with both octane and cycles, depending on whether we need high dynamic range for a scene or not. It would be a big help if we could output untomemapped images with octane as well.

For our current project it is crucial to output images with dynamic range -- in other words, color values must be saved with floating point precision and must not be clamped between 0.0 and 1.0. I have searched the forum and found out that there should be an option to save images as untonemapped EXR ...