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4.19 Physical Lights

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    Originally posted by rosegoldslugs View Post

    That's correct. The range between the sun light and pretty much anything else, practical or natural, is extremely high. Even the range of the sun itself between noon and sunset is pretty extreme. The Lux values also include the sky contribution, so your light value will be slightly lower.

    For night time exterior, you'd use an EV of -6 to 4, depending on what type of light your subject is under, including moon phases. For night interiors, an EV of 4 to 8 also depending on what type of light is used. If you want to use the manual controls, pick from the chart here that corresponds to your desired EV and f-stop. https://en.wikipedia.org/wiki/Exposu...amera_settings

    That means a value of 1Lux for the directional light "moon" is correct? The problem i have with the current physical lighting setup in Ue4 is, 1Lux gives me no lighting at all in my scene.
    I also have a problem with this data charts, i don't really know how to match the terms in the charts with the editor ones, f number is a clear thing, it's the f-stop in the editor... values like 1/125, 1/100 or 1/30 are the shutter speed values.. but where are the ISO numbers ? I guess they are always the same like the shutter speed? And what is EV ? Exposure Values... Is it the Min and Max Brigthness in the Exposure tab ? or the Exposure Compensation value ?

    The chart gives me also shutter speed values like 1 or 2 or 60, without the 1/ , the same goes for 2m, 4m, 8m, up to 256m and so on... how should i use this values ?

    And for the simple sunny 16 rule setup like from Daedalus51's video, Lumen and Candela values are still absolutely not working for me.
    Last edited by A-J-K; 11-20-2018, 10:28 PM.

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      Originally posted by A-J-K View Post
      That means a value of 1Lux for the directional light "moon" is correct? The problem i have with the current physical lighting setup in Ue4 is, 1Lux gives me no lighting at all in my scene.
      I also have a problem with this data charts, i don't really know how to match the terms in the charts with the editor ones, f number is a clear thing, it's the f-stop in the editor... values like 1/125, 1/100 or 1/30 are the shutter speed values.. but where are the ISO numbers ? I guess they are always the same like the shutter speed? And what is EV ? Exposure Values... Is it the Min and Max Brigthness in the Exposure tab ? or the Exposure Compensation value ?

      The chart gives me also shutter speed values like 1 or 2 or 60, without the 1/ , the same goes for 2m, 4m, 8m, up to 256m and so on... how should i use this values ?

      And for the simple sunny 16 rule setup like from Daedalus51's video, Lumen and Candela values are still absolutely not working for me.
      1 Lux will only be visible if your exposure is correct. Night time can get into the negative EVs, so 1 Lux will absolutely be visible then. EV is a simplified way of talking about exposure. Just gonna quote myself here cause I'm lazy
      Originally posted by rosegoldslugs View Post
      It's a single unit based on shutter speed, ISO(generally 100), and f/stop to where any combination that has equal exposure to another combination would use the same EV. Instead of worrying about the individual settings, you can use the EV input. Plus, it provides a real-world measured reference that can get you 90% of the way there just like other physical units. For instance, interiors will likely be around 4 - 8 because of the average luminance found in interiors, but with Auto-Exposure now directly using EVs, we can also adjust for the exposure outside if you get near a window, like up to 13 for the overcast day outside in my scene...

      ...An EV of 5 is identical to a shutter speed of 1/4s with an f-stop of 2.8 at ISO 100. It's also identical to a shutter speed of 1s, ISO 100, and a f-stop of 5.6 because both combinations of settings will result in identical exposure. EV5 is just a simpler way to put it.
      They're used in the engine by default as the viewport exposure override, unless you enable the extended range option in the Project Settings, which will replace the Min/Max Exposure values for EVs in the Post-Process Volume. Regardless, the Manual mode can achieve identical results, you just have to convert the single EV value to the individual camera settings.

      To use the chart for matching EV to manual settings, just set your Post-Process Volume's Metering Mode to Manual and set the correct values down in the Camera section. Most measurements will be based on ISO 100, that chart included. So because of that, and because the Shutter Speed input is limited to 1/1(1 second), some of the chart is irrelevant. You could do some math to get the required Shutter Speed and F-Stop for a different ISO, but since the manual settings don't really change anything else it doesn't matter imo.

      Considering that the Sunny 15/16 rule is targeted towards exposing for a subject in direct sun on a clear day, I wouldn't expect your every day light to be visible then. It's the same concept of your car's headlights not visible during the day, excluding the actual light emitting surface since that is always waaaaay brighter. Or your phone screen not being visible out in the sun or it blinding at night.

      Last edited by rosegoldslugs; 11-21-2018, 12:39 AM.
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        @rosegoldslugs


        Sorry to butt in, but I've got some questions. I'm not sure how shutter speed works with UE4, generally I've heard for video with DSLR cameras, you want to lock the shutter speed to half the frame rate, in order to get an appropriate amount of motion blur. I doubt exposure/motion blur work the same in game engines as they would on a camera (motion blur is a post effect controlled with a value not linked to the camera shutter speed, right?). If shutter speed doesn't directly effect the motion blur, why would you use that over just changing the iso? There's no downside to cranking up the ISO since you don't have to deal with camera noise.

        Or am I miss understanding how ISO and shutter speed work in UE4.


        I probably just need to play with the camera settings more, I've mostly just played with the exposure values and ignored trying to use it like a DSLR.

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          Originally posted by ZacD View Post
          @rosegoldslugs


          Sorry to butt in, but I've got some questions. I'm not sure how shutter speed works with UE4, generally I've heard for video with DSLR cameras, you want to lock the shutter speed to half the frame rate, in order to get an appropriate amount of motion blur. I doubt exposure/motion blur work the same in game engines as they would on a camera (motion blur is a post effect controlled with a value not linked to the camera shutter speed, right?). If shutter speed doesn't directly effect the motion blur, why would you use that over just changing the iso? There's no downside to cranking up the ISO since you don't have to deal with camera noise.

          Or am I miss understanding how ISO and shutter speed work in UE4.


          I probably just need to play with the camera settings more, I've mostly just played with the exposure values and ignored trying to use it like a DSLR.

          No I'm in the same boat as you. I don't see the point in even using the manual options. The cinematic camera/ new DoF are based on physical sensor and lens settings, but I haven't seen anything where they're tied together so really I have no idea what else they'd be used for other than people wanting to match a particular setup for a very specific reason.
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            Originally posted by rosegoldslugs View Post


            No I'm in the same boat as you. I don't see the point in even using the manual options. The cinematic camera/ new DoF are based on physical sensor and lens settings, but I haven't seen anything where they're tied together so really I have no idea what else they'd be used for other than people wanting to match a particular setup for a very specific reason.
            Right now, I can really only use the manual settings as a sanity check for my values. But currently there's no way to "eye adapt" between EV values in manual, so I'm forced then to use Histogram/Basic for getting that effect, but those values have no correlation to real life values. I get it - Unreal has to support legacy projects and such, but it's just not at all intuitive of what values should be. Like Daedalus51, I'd love to have the option of a "Min/Max Aperature/F-stop" adaptation in manual mode. This way I know for sure what a scene should be looking like, since I would have real life equivalent to compare to.
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              Originally posted by k.mermelstein View Post

              Right now, I can really only use the manual settings as a sanity check for my values. But currently there's no way to "eye adapt" between EV values in manual, so I'm forced then to use Histogram/Basic for getting that effect, but those values have no correlation to real life values. I get it - Unreal has to support legacy projects and such, but it's just not at all intuitive of what values should be. Like Daedalus51, I'd love to have the option of a "Min/Max Aperature/F-stop" adaptation in manual mode. This way I know for sure what a scene should be looking like, since I would have real life equivalent to compare to.
              It's a bit of a process, but you could use the chart on the Wikipedia page I linked above and use the Min/Max EV(once you enable extended range in the project settings) and use EV values based on your desired manual settings at ISO 100. With the correct settings, there's a very tiny difference between Manual mode and a corresponding EV. I haven't tried the default min/max settings, but yeah I'm assuming since it's not with the extended luminance range, the values don't necessarily line up with the huge range required.
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                Originally posted by rosegoldslugs View Post

                It's a bit of a process, but you could use the chart on the Wikipedia page I linked above and use the Min/Max EV(once you enable extended range in the project settings) and use EV values based on your desired manual settings at ISO 100. With the correct settings, there's a very tiny difference between Manual mode and a corresponding EV. I haven't tried the default min/max settings, but yeah I'm assuming since it's not with the extended luminance range, the values don't necessarily line up with the huge range required.
                Thanks - I have not turned on the extended range in project settings, I'll look into that.

                But I think the point too overall is that it's still a bit involved process, when this sort of thing should be a lot easier to work with. Those us hanging out in a photorealism space would appreciate a little more out of the box solution. I really like the idea of using manual because I have real life photographic data and images to compare to, and I'm a bit disappointed that this isn't a feature in Unreal when I've used this sort of system in nearly any other engine I've worked in.
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                  First of all thank you for clarifying my points rosegoldslugs!
                  As k.mermelstein mentioned, things are waaaay to complicated at the moment, on top of that some of the values like lumen are not really working like they should. I hope the next versions of Ue4 will support physical lighting like it should be, you put your real life values into the editor and you get the right lighting result back.

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                    Originally posted by Daedalus51 View Post

                    Why is the camera exposure setting in line with sunny 16 but the one system I need to use to have a range of lets say f8 to f10 for gameplay is not? Thats my only issue with this Its for the sake of understanding it better and streamlining it for less experienced people. Also it would be easier touse the samevalues for cutscenes and gameplay (with the difference that gameplay would have a range of a few stops if you want)

                    Cheers!
                    I'm not sure if anyone answered exactly yet why this example doesn't work so I wanted to clarify. f/8 is not the same as EV100 8. Aperture is only one variable in the equation and EV100 is the total result.
                    • The first image is using fixed exposure of EV100 8
                    • The second image is using 1/125s, f/8, and ISO 100 it looks like.
                    Maybe it'd be nice to work with variable shutter or f-stop (or ISO), but the result is always a brighter or darker image and EV100 gives us this in one simple number. Documentation would help

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                      I just got 4.21 and am back at this.
                      Can't get my head around it as usual.

                      At 125000 lux and sunny 16 settings why is my desert so dark?
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                        Bump. whether I use manual settings or putting EV100 on 16, I'm getting same dark results. Really need some help with that.

                        I'm not even sure if I'm doing it wrong or it just doesn't work properly, like before.
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                          1/125, ƒ16, and ISO 100 is closer to EV15. With a pure white card, fully rough facing up, I increased the sky brightness until the card read about 25,000 Lux. I increase the sun to about 135000 Lux, bringing the final card reading to 125,000 Lux. With these settings, the previous values work well(also pretty close to perfect exposure for 18% gray), but EV16 is pretty dark, but if we follow typical EV measurements, EV16 is mainly for bright subjects on snow or sand, which explains why it's much darker than we expect. EV15, for 1/125, ƒ16, at ISO100 should look correct provided the intensities are all accurate and your materials are in the proper range.

                          Try raising your sun angle to be more in line with a mid-day angle and increase the intensity. Also try measuring a white card with the Pixel Inspector. My sun at 135000 is only about 99,000 Lux, so that's probably why it looks so dark to you.

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                            Originally posted by Maximum-Dev View Post
                            I just got 4.21 and am back at this.
                            Can't get my head around it as usual.

                            At 125000 lux and sunny 16 settings why is my desert so dark?
                            Are you using a custom skydome ? If so, you also need to crank up the brightness multiplayer of your HDRI.

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                              Originally posted by rosegoldslugs View Post
                              1/125, ƒ16, and ISO 100 is closer to EV15. With a pure white card, fully rough facing up, I increased the sky brightness until the card read about 25,000 Lux. I increase the sun to about 135000 Lux, bringing the final card reading to 125,000 Lux. With these settings, the previous values work well(also pretty close to perfect exposure for 18% gray), but EV16 is pretty dark, but if we follow typical EV measurements, EV16 is mainly for bright subjects on snow or sand, which explains why it's much darker than we expect. EV15, for 1/125, ƒ16, at ISO100 should look correct provided the intensities are all accurate and your materials are in the proper range.

                              Try raising your sun angle to be more in line with a mid-day angle and increase the intensity. Also try measuring a white card with the Pixel Inspector. My sun at 135000 is only about 99,000 Lux, so that's probably why it looks so dark to you.

                              I have several questions but, how do you measure the surface illuminance? I don't see such option in pixel inspector nor HDR visualizer.

                              Originally posted by A-J-K View Post

                              Are you using a custom skydome ? If so, you also need to crank up the brightness multiplayer of your HDRI.
                              I do, I just had hidden it in that picture. Wondering about how to measure surface illuminance though.
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                                Originally posted by Maximum-Dev View Post
                                I have several questions but, how do you measure the surface illuminance? I don't see such option in pixel inspector nor HDR visualizer.
                                William.sch documented a good method a few pages back, which is similar to what I do at work as well. Essentially, you can do it from a sphere(easy to sample from any direction) or use a plane oriented towards any particular direction you want to measure. The material on either mesh needs to be pure white(1.0, not PBR white) and fully rough. If you lay the plane flat, horizontally, you're recreating a horizontally placed light meter, which is usually the case since IRL you don't really want to burn out the meter by pointing it directly at the sun.

                                With the Pixel Inspector enabled, and you're in game mode(nothing will happen if you're not), you can sample an area on the mesh. For the sphere, it's most likely the direction of the dominant light source or the top pole. For the plane, it's anywhere on the top face. It's a good idea to disable bloom, fog, DFAO/SSAO, and any other post-effect that might interfere with the scene color. The HDR input in the Pixel Inspector measures everything in luminance or cd/m² or nits, which is why you want to use a pure white material since luminance is based on color. Taking that HDR value and multiplying it by pi will give you the Lux value.

                                Lux is easier to find for any given lighting condition. Luminance is a good measurement if you're really trying to nail a sky material or emissive surface. With most Lux measurements online, they will include the sky contribution too. I will usually measure the skylight by itself and then the sky and sun to get the ambient in range first before the sun, since the sun measurement on a Lux meter can vary drastically based on the angle of the sun and card.
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