Author Topic: (Daily Build 2020-02-27 & v5) - Huge issue with final frame gamma  (Read 559 times)

2020-03-30, 15:12:23

Nejc Kilar

  • Active Users
  • **
  • Posts: 959
    • View Profile
    • My personal website
Hello yet again! :)

So we all know that there is a noticeable gamma difference between the PV and the VFB - this was reported before. The problem however is that the gamma difference can be incredibly different when dealing with contrasty scenes.

In my case, I was rendering out a product viz on a black background and the noticeable difference was HUGE enough so that I couldn't deliver the pre-final preview frames to the client because it just wasn't representative of the frames we did before. The gamma difference was simply too big.

That then begs the question as to how are we supposed to use Corona to render animations and moody / contrasty interiors? You can't use the render queue to save out files because that makes it go through the Picture Viewer which messes up the gamma. You also can't "save" files over night because the saving mechanisms again make it all go through the Picture Viewer which results in... The wrong gamma :)

So right now, if I want my VFB to match my output I literally need to have an alarm clock every 4 hours so that I can save the files and set everything to render from the next angle. If I don't do that, well, I might just send my clients weirder and darker images than what I've got set up in the VFB. And no, if you render in 8 or 16bit (non linear, obviously) there is very little you can do to correct the issue.

The above hopefully illustrates that this is a huge issue. It was reported at least a couple of times throughout the years and if we want to make Corona fully production ready I am definitely of the opinion that this must be fix.

Oh and just to make it clear, there are scenes that render out with a relatively small difference that even a trained eye can hardly spot. Typically, at least thats my impression, those scenes are well lit interiors and the like. As soon as you go for something more dramatic / dark the whole thing falls apart because the gamma just gets really messed up.

Check out the bellow attachments. Overlay them on top of each other and then turn one of the layers off - you'll see its a really big difference. (The product changes a bit because of the IR not properly handling the geometry compared to the final frame (a bug of its own but its workable). I haven't bothered creating another preview but rest assured, even if you delete the model and just leave the background the issue with the gamma is alive and well.)

Hope it helps :)

2020-04-03, 23:24:14
Reply #1

Nejc Kilar

  • Active Users
  • **
  • Posts: 959
    • View Profile
    • My personal website
Another cropped example :)