Conclusion
Again, I have to stress that the difference screenshots are brightened for better viewing and are not as severe as they initially appear. Almost all of these intermediate formats hold a decent amount of detail throughout rounds of recompression with the only, surprisingly, stand out failure being Avid’s implementation of their own DNxHD codec because of severe visible blocking. Apple’s official ProRes codec seems to perform the best in terms of introducing the least amount of artifacts after 5 generations.
So what exactly is the take away if you won’t see this level of compression “in the wild”? It seems that Avid’s DNxHD either has more aggressive compression or pre filtering/blurring than the other codecs which may lead it to being less suitable for a greenscreen intermediate than ProRes or Cineform. Cineform may be sacrificing color fidelity to keep sharpness and edge detail; because of its uncontrollable bitrate it may be a hard 1:1 comparison. ProRes may be striking some kind of balance between overall fidelity and sharpness. Different design philosophies from each codec