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4.19 Physical Lights

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    #61
    Also LPVs don't work when using manual metering mode. Reverting back to non-physically based lighting. Thanks for the hype epic. :3
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      #62
      Originally posted by Uriel.Doyon View Post
      Hi,

      Some more details on the new exposure settings in 4.19 :

      - The exposure value from the viewport EV100 slider is defined as Exposure = 1 / (1.2 * 2^EV100)
      - The relationship with the PPV camera setting is EV100 = log2( N^2/t * 100/S ) where N is the aperture, 1/t is the shutter speed and S is the ISO.
      - The scene color is defined in cd/m², before the exposure is applied. It can be inspected by using the PixelInspector tool.
      - To isolate the effect of exposure on the final color, disable the "tonemapper" post process in the show flags.
      - Directional lights and sky lights units are in lux.
      - When using the "manual" metering mode, the scene can go dark because the default values define an EV100 of 9.91 (where as most scene are made for an EV100 of -1.2).
      - When using auto exposure with realistic lighting values, increase "Max Brightness" to 10K and "Histogram Log Max" to something like 16. Otherwise, it will go white.
      - Prior to 4.19, the point lights units suggested to be in lumens but it was not in practice.
      - IES profiles work in the unit type of the lights.

      Uriel

      Uriel.Doyon
      The sky light is definitely not using units of Lux, it actually appears to use units of cd/m^2, could you please clarify?
      I tested the sky light by capturing a perfectly white sky sphere (measured with the pixel inspector to have a scene color / hdr luminance of 1.0) and using this to light a perfectly diffuse white sphere. Testing the luminance of the sphere with the pixel inspector reports a luminance value that is almost exactly 1.0 cd/m^2. Which suggests that the sky light is, in fact, using units of cd/m^2 and not lux (lm/m^2). A directional light of intensity 3.14 is required to get similar luminance values on the brightest part of the sphere. This makes sense since a purely diffuse BRDF would just multiply the incoming Illuminance (Lux) by 1/pi to convert to outgoing Luminance (cd/m^2). So either the sky light is actually a luminance value (cd/m^2), or someone forgot to multiply by 1/pi somewhere, but I'm guessing it's the former.

      The second issue I have is that the HDR Luminance values I read from the pixel inspector don't seem to match up to a given EV100 value. For instance, I created a room lit entirely by a single point light of 1400 Lumens with a temperature of 3000K. The room was roughly modeled off the dimensions of my bedroom, the lumens and temperature values of the light bulb were taken from the actual bulb that lights the room. Using my phone camera (it has a manual mode where I can check ISO, shutter speed, and f-stop) I know that I need an EV100 of about 5 for this room to look correct. Using these values the room does actually appear correct, however, when I look at the pixel inspector I see an average HDR Luminance value of around 20. From the Wikipedia page of exposure values (https://en.wikipedia.org/wiki/Exposure_value, table 3) I can see that for an EV100 of 5 I would expect an average scene luminance of about 4 cd/m^2 which does not match up at all with the values I am getting.

      I'd also like to get some more info about this exposure formula (Exposure = 1 / (1.2 * 2^EV100)).
      Where exactly does this come from? in particle the 1.2 value?
      I assume by exposure here you mean the average scene luminance in cd/m^2 that the game will adjust to?

      Originally posted by Daedalus51 View Post
      EDIT: okay, interesting find! The 1000 lumens light was suuuuper dark, so I had to use 100 000 lumens instead. I thought, what happens if I use candela instead? So with a converter, I found out that my 1000 lumens light would translate to 75 000 candela. After I put 75 000 candela into the lights value in Unreal, it actually looked correct! Like what the heck is happening here? XD
      Daedalus51
      I think your math might be a bit off here. A 75000 candela spot light with a cone angle of 45 degrees would be equivalent to the same spot light with about 138000 lumens. So your 100000 lumen light actually matches up with the candela value you used.
      Last edited by FurryFur; 04-25-2018, 04:41 AM. Reason: Edited out incorrect information regarding possible bug.

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        #63
        Originally posted by Daedalus51 View Post
        ...
        Also, in relation to why realworld values are great...let me give you the following example:

        I did some lighting on Theed City, Naboo for Battlefront 2. So lets look at a shot here

        Click image for larger version Name:	BF2_1.jpg Views:	1 Size:	488.6 KB ID:	1455738

        So...this is a sunny setting with pretty strong lighting and a bright sky....so what do I know?

        I know that I need a sunlight intensity of around 125 000 lux
        I need a MAX EV value of around 16 based on the sunny 16 rule
        We also measured sky luminance for different settings so I know that the sky like I want it should be around 5000 cd/m2

        With all this data, setting up the lighting for Naboo becomes a **** cakewalk!

        First, I tweak exposure to be EV 16 and I crank up the sunlight to 125 000 lux. Then, I add an HDRI skydome and turn on the exposure viewmode that has a square in the center of the screen....inside that square, it measures luminance and shows me the value. I look at an average spot on the sky with the square and bump up the sky brightness until the number in the square reads 5000 cd per square meter.

        DONE!

        Now my local lights will AUTOMATICALLY ALWAYS be correct since they use lumens and all these values work in relationship. Now I can focus and the actual ART of lighting instead of getting the **** basics done. This whole thing took me less than 10mins to setup and it looks almost perfect right out of the box!

        So why exactly can't we have something like this? Can anyone give me a really good reason to NOT do this?

        Cheers!
        THANKS for sharing your settings!! Beautiful lighting.
        So the sky brightness in this scene is 5000 cd per square meter. What value would this be in lux? Lux is lumen per square meter and the internet seems to suggest that I can simply convert 1:1, therefore 5000 lux? This would be suspiciously simple. So the skylight has 4% the intensity of the sunlight?
        Last edited by Xharthok; 05-08-2018, 02:00 AM.

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          #64
          Xharthok
          If you have the average luminance of the sky, then you should be able to multiply by pi to get the corresponding average Lux value (Note that in my above post I actually deduce that Unreal's skylight units are already in cd per square meter and not Lux as stated by Uriel). You can test this in unreal by placing a perfectly white, 100% rough, 0% metallic, 0% specular, ball in the scene and checking its luminance values with the pixel inspector. A directional light with a lux value of 3.14 (pi) will produce a luminance of 1 at the highlight. Creating a perfectly white sky sphere (make sure it's luminance is 1 when hovering over sky with the pixel inspector if using bp_sky_sphere, as it has weird output) and using it as the input for a skylight, will produce a ball with luminance values of 1 spread over the entire surface of the ball.
          Last edited by FurryFur; 05-14-2018, 08:52 AM.

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            #65
            Did physical lighting become obsolete already? Epic?
            Thread dates back to January and there's still no support.
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              #66
              Maybe we have to move this to the "Feedback for Epic" section and bump like crazy? Maybe even push this thread via Twitter? I think if we make enough people see and react to it, Epic HAS to respond at some point before it turns into negativity. I don't like doing it like this, but man, if they continue to ignore this, let's fight the good fight!
              Check out UNREAL 4 Lighting Academy
              https://forums.unrealengine.com/show...ng-like-that-)

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                #67
                Originally posted by "Daedalus51 ;n1484543"
                Maybe we have to move this to the "Feedback for Epic" section and bump like crazy? Maybe even push this thread via Twitter? I think if we make enough people see and react to it, Epic HAS to respond at some point before it turns into negativity. I don't like doing it like this, but man, if they continue to ignore this, let's fight the good fight!
                kenpimentel Amanda.Bott Chance Ivey Kalvothe

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                  #68
                  Twitter post is out! Share and retweet as if your lights depend on it!
                  #AllLightsMatter :P

                  https://twitter.com/tillederdon/stat...49008411942912
                  Check out UNREAL 4 Lighting Academy
                  https://forums.unrealengine.com/show...ng-like-that-)

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                    #69
                    Originally posted by Daedalus51 View Post
                    Twitter post is out! Share and retweet as if your lights depend on it!
                    #AllLightsMatter :P

                    https://twitter.com/tillederdon/stat...49008411942912
                    Retweeted

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                      #70
                      Hey all,

                      Let me catch up on this thread and I'll get back to you with one direction or another! Just so you know, I have not been avoiding it, just a super busy time with things going on, I apologize for that!

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                        #71
                        Originally posted by Kalvothe View Post
                        Hey all,

                        Let me catch up on this thread and I'll get back to you with one direction or another! Just so you know, I have not been avoiding it, just a super busy time with things going on, I apologize for that!
                        <3 <3 <3

                        Thx Kalvothe !!
                        Check out UNREAL 4 Lighting Academy
                        https://forums.unrealengine.com/show...ng-like-that-)

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                          #72
                          Hey guys,
                          I have pinged some of our teams on this. We're in the thick of getting stuff ready for 4.20 so give us some time to put together a response. I know you've been waiting patiently and I promise I'll stay on top of it, but I ask for a bit more time.

                          :-)

                          Thanks!

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                            #73
                            Originally posted by Kalvothe View Post
                            Hey guys,
                            I have pinged some of our teams on this. We're in the thick of getting stuff ready for 4.20 so give us some time to put together a response. I know you've been waiting patiently and I promise I'll stay on top of it, but I ask for a bit more time.

                            :-)

                            Thanks!
                            Thank you! Just a suggestion, it was mentioned above, but I'll say it again. Please, make working presets. It's a best way to show how everything works together. Scene with super simple exterior and interior. Light scenarios-bright day, cloudy, night. Artificial light in the interior. Dynamic and baked versions. I doubt if anyone will be unhappy with it.

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                              #74
                              so I may have found why the exposure isn't working properly. I was looking through the trello ( https://trello.com/c/d1MUZwNk/218-physical-light-units ) today after the 4.20 pre-release came out and found this under the 4.19 physical light post. It looks like the EV100 option under metering mode is missing.
                              3D Artist & Virtual Reality Specialist

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                                #75
                                Originally posted by BryanChrisBrown View Post
                                so I may have found why the exposure isn't working properly. I was looking through the trello ( https://trello.com/c/d1MUZwNk/218-physical-light-units ) today after the 4.20 pre-release came out and found this under the 4.19 physical light post. It looks like the EV100 option under metering mode is missing.
                                Daedalus51

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