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    There are some light bleeding in my scene with GPU that wasn't there with CPU.
    Any advice to get rid of then?


    Click image for larger version

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      Originally posted by BoothStudios View Post
      Hey everyone - I'm late to the party as I was on a mac previously. I just completed my first render with this amazing tool.
      First is GPU, second is CPU. There are quite a few differences, including color temp. Also time savings. GPU took a third of the time it took to render CPU.

      Thank you Luoshuang!
      CPU one looks more atmospheric IMO. Did you find a way to make GPULightmass image to look like CPULightmass one ?

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        I wonder if new GPULightmass is coming when 4.22 is out

        Comment


          Originally posted by Sanjuan View Post
          There are some light bleeding in my scene with GPU that wasn't there with CPU.
          Any advice to get rid of then?


          Click image for larger version

Name:	Screenshot_14.jpg
Views:	199
Size:	108.1 KB
ID:	1575315
          hi,
          same issue for me. I thought the problem came from the mesh itself or from the way i unwrapped uvs, so I spent half of the day to figure it out, trying several methods of modelling and unwrapping. but no result. So I focused on my shader (a basic white material). I simply add a constant 1 to the roughness ... problem solved. oO

          Comment


            Originally posted by NicoMRGR View Post

            hi,
            same issue for me. I thought the problem came from the mesh itself or from the way i unwrapped uvs, so I spent half of the day to figure it out, trying several methods of modelling and unwrapping. but no result. So I focused on my shader (a basic white material). I simply add a constant 1 to the roughness ... problem solved. oO
            Very strange...
            But i will try that...

            Comment


              Originally posted by Sanjuan View Post

              Very strange...
              But i will try that...
              And I also turned off "two sided"....

              Comment


                Originally posted by motorsep View Post

                CPU one looks more atmospheric IMO. Did you find a way to make GPULightmass image to look like CPULightmass one ?
                There's no such thing as more atmospheric. There's just bias. If one looks significantly different from the other in terms of light transport (brightness, amount of color bleeding, darkness of indirect shadows), then the one or the other is doing something really wrong
                https://www.artstation.com/artist/rawalanche

                Comment


                  Originally posted by Luoshuang View Post
                  Hi! I ask you if when the version 4.22 revolution arrives the lightmass calculation will still be CPU or Luoshuang will also provide us a GPU calculation. Currently all my lightmass calculations are in GPU and since I have to change my computer I wanted to know whether to invest in a CPU with a very high number of threads (36 in case the GPU calculation is excluded in 4.22) or medium (20 for the calculation only of distance fields). Thanks!

                  Comment


                    Originally posted by Rawalanche View Post

                    There's no such thing as more atmospheric. There's just bias. If one looks significantly different from the other in terms of light transport (brightness, amount of color bleeding, darkness of indirect shadows), then the one or the other is doing something really wrong
                    Sounds like something a programmer would say :P

                    CPU one looks better, more cinematic if you will, IMO.

                    Comment


                      ^ I actually feel much better with the GPU screenshot. The CPU screen feels otherworldly. The blue hues in the GPU shot feel much more grounded in reality.

                      it seems like the GPU version took more influence from the skylight.

                      Im not an expert, so idk what’s more correct.

                      Comment


                        Originally posted by Nerdsbeware View Post
                        ^ I actually feel much better with the GPU screenshot. The CPU screen feels otherworldly. The blue hues in the GPU shot feel much more grounded in reality.

                        it seems like the GPU version took more influence from the skylight.

                        Im not an expert, so idk what’s more correct.
                        That's the whole point. For archviz or realistic scenes you might want to have that effect that GPULightmass provides, however, for games (that need to be otherworldly) you want that otherworldly feel that CPULightmass provides (but I'd love to get that feel using GPULightmass and short lighting build times )

                        Comment


                          Originally posted by motorsep View Post

                          That's the whole point. For archviz or realistic scenes you might want to have that effect that GPULightmass provides, however, for games (that need to be otherworldly) you want that otherworldly feel that CPULightmass provides (but I'd love to get that feel using GPULightmass and short lighting build times )
                          There's no otherworldly feel, that's just bias

                          Seriously though. I have a lot of experience from almost a decade spent being CG generalist (doing offline graphics). Even in offline graphics, people were using some really bad workflows up until not that long ago, and they also often excused them by artistic choice, attributing some artistic qualities to certain errors in light transport accuracy. But I don't know of a single person who actually learned physically based workflow, and then wanted to go back to the previous workflows to achieve that old aesthetic caused by inaccurate, biased lighting.

                          The point here is that in both cases you can achieve very similar aesthetic, just at a different point in a workflow. If you want to have darker, more contrasty interior, you don't do that by messing with light transport, but you can achieve more or less same result with messing with post process settings, reducing the brightness of the scene and increasing contrast. But unlike achieving that by breaking the light transport, if you do it the correct way, you will still preserve the relation of light, so the version where you have achieved it through post process will always look better to human eye.

                          Problem here is that in UE4, both CPU and GPU lightmass have some issues with the accuracy, but that's to be expected given the usage for realtime graphics, so often one doesn't have a choice. But if you do, always choose the more accurate way, if the performance is similar.

                          That being said, looking at the renders above, CPU vs GPU lightmass, it actually confirms my point. The CPU version here does clearly a lot less clamping of the sun light bounce transferred from the floor to the ceiling. It's actually more physically accurate compared to the GPU lightmass one, which clamps way too much. Clamping in this context is a method to prevent fireflies caused by high contrast areas, you can find out more here: https://forums.unrealengine.com/deve...ghtmass/page10 . It was actually me who recommended it, but clearly, GPU lightmass seems to use it way too agressively. Non the less, the one you've considered better looking is also the more accurate one
                          https://www.artstation.com/artist/rawalanche

                          Comment


                            Originally posted by Rawalanche View Post

                            There's no otherworldly feel, that's just bias

                            GPU lightmass seems to use it way too agressively. Non the less, the one you've considered better looking is also the more accurate one
                            @BoothStudios To investigate, lets tune up FireflyClampingThreshold in BaseLightmass.ini to some value like 10000.0 and see whats happening

                            Comment


                              Luoshuang

                              How is new version of GPULightmass coming along?

                              Comment


                                Urgent question: Can I install GPU files from 4.21 to 4.21.2?

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