Please allow me resurrecting this thread, because it's the first google result when I search about compression artefacts in DSLR videos. So I wanted to add something I figured out.
The reason, CineForm's FirstLight has artefacts on 8-bit material, and not on AFter Effects is not your dithering and interpolating. FirstLight changes the metadata of the file and not the actual footage to "color correct" it. So there is no 32-bit floating. And Premire / After Effects do the upscaling internally, as DFM stated.
CineForm revealed to be completely useless when trying to avoid artefacts in color grading when using a good NLE with 32-bit-float.
The reason, CineForm's FirstLight has artefacts on 8-bit material, and not on AFter Effects is not your dithering and interpolating. FirstLight changes the metadata of the file and not the actual footage to "color correct" it. So there is no 32-bit floating. And Premire / After Effects do the upscaling internally, as DFM stated.
CineForm revealed to be completely useless when trying to avoid artefacts in color grading when using a good NLE with 32-bit-float.