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Iray, color transforms, and dynamic range.

lemipslemips Posts: 23
in Technical Help (nuts n bolts)

Howdy!

I think its pretty safe to say that dynamic range is one of the most universal struggles in rendering. Everyone has had an indoor scene and tried to light it with a sun-sky dome through a window, only to have the room dark as a cave while things in direct sunligh are completely washed out and clipped into oblivion. 

Recently I saw a video entitled The Secret Ingredient to Photorealism-

https://www.youtube.com/watch?v=m9AT7H4GGrA

-by a channel called Blender Guru. I'm sure some have seen it but I will summarize: He demonstrates this exact problem in Blender, and goes on to explain that the culprit is buried deep in the renderer, where Blender used a completely inappropriate color transform, sRGB, to turn render information into information your monitor can use. The fossilized color manager was meant for boxy old crt monitors, not modern panels. It butchers color information, crushing dynamic range down to a few stops no matter how well your scene is lit, a level that a disposable film camera would laugh at. The problem went unoticed because the technical field of color has very few experts. At the time of the video one of those experts, Troy S, had fixed the problem in blender by making a custom color management thingy freely available, Filmic Blender.

Does anyone with more knowledge of Iray and Daz's inner workings know for sure if we also have this problem? Going on my own experience with lighting, I would be very, very surprised if we don't. Blender has a very easily accessed option to select a color manager, I have yet to find any options in Iray or any discussion of this in the forums. If Iray does use sRGB, and even if this cannot be fixed with a 3rd party package like it was in Blender, perhapse we can bring this to light (heh) in hopes of it being solved internally. 



Note, as usual with this sort of thing, if this discussion already exists and the ever obscuring fog of the forum's terrible search function has hidden it from me, appologies!

Comments

  • PaintboxPaintbox Posts: 1,633
    edited May 2020

    Checkout this thread, where are discussing this issue :

    https://www.daz3d.com/forums/discussion/313401/iray-photorealism#latest

    I actually use the filmic workflow right now. I render an EXR with tonemapping off and post process it with filmic.

    Post edited by Paintbox on
  • PadonePadone Posts: 3,476
    edited May 2020

    That video by Andrew is highly inaccurate. The srgb space has nothing to do with the transfer function and it's a very good output for standard monitors, so there's nothing bad about it.

    As for iray you can get a "filmic" transfer the same as blender by turning off burn highlights and crush blacks in the tone mapping panel.

    http://docs.daz3d.com/doku.php/public/software/dazstudio/4/referenceguide/interface/panes/render_settings/engine/nvidia_iray/tone_mapping/start

     

    edit. I'd add that using a "filmic" transfer is not necessarily better than a "standard" transfer, it all depends on what you need. To simulate real cameras the "filmic" transfer is not good.

    Post edited by Padone on
  • Rev2019Rev2019 Posts: 167
    edited June 2021

    SDR is the problem here

    to get the real high dynamic range you need to renderer 32 bit canvases.

    adjust "brightness" with the Exposure setting in PS

    save it as HDR image.

    then in Win10 with an HDR capable tv select "Use HDR" under System settings

    then use the HDR+WCG image viewer to watch the renderer in HDR10 format.

    the difference is amazing.

     

    i have done HDR10 renderers for about a year now.

    lets say that you can increase brightness levels to insane levels and still not clip any highlights.

     

    This is the SDR version but the HDR10 verison has MaxCLL: 4308 Nits

    if your tv has around 1500 to 2000 nits these Neon lighs shines in a way they never do in SDR.

    The HDRi sky glows in a way you have never seen before

    And all details are there.

    HDR10 is the solution to your low dynamic range problems

     

    But how good your HDR10 renderer will look depends on the TV.

    The Best Sony tvs today can do 2000 Nits (Sony Z8H 75")

    There is only one tv i know about that can display this renderer as it should look at 4000 nits glowing neon lights and its the 2019 Sony ZG9

     

     

     

     

    Art Deco Miami .jpg
    2160 x 2160 - 3M
    Post edited by Rev2019 on
  • Rev2019Rev2019 Posts: 167
    edited June 2021

    .

    Double post

     

    Post edited by Rev2019 on
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