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Vray Sun/Sky - Photo Comparison

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  • Vray Sun/Sky - Photo Comparison

    I have been trying to understand how the Vray Sun/Sky + Vray Physical Camera combination relates to real world conditions. To test, I created a simple physical model that I photographed and built a similar 3D model that I rendered trying to match conditions and settings. I've shown the results below.

    I immediately noticed that the Vray Sky seems to have much more cyan than does our sky in the mountain west US. No matter how I tried to adjust the color balance, I couldn't match the real world. I also tried putting the sky in an output map and adjust but that didn't help (but I don't know that much about how to use the output map).

    The second thing I noticed was that the light bouncing off the cube was more intense in the model than in the photo. I played with the Primary and Secondary bounces but couldn't match the photo. I didn't try reducing the "generate GI" values, which would probably help.

    I also discovered that almost without exception, the Vray Physical Cam was one stop brighter than the real camera. I either had to reduce the f-stop one stop or the ISO by 1/2 or increase shutter by 2.

    Overall, I was very impressed at how quickly I was able to approximate the real world by using many of the default settings, the exception being the white balance. I hope that anyone who has had good luck replicating the real world will offer suggestions that will help me understand how to get better results.

    Craig

    Settings:
    Gamma (display, input & output) 2.2
    Mapping Linear multiply, 1,1,1
    GI Primary IR, Secondary Brute Force
    Medium Preset, HSph50, Int Smpls 20
    Overcast Day Physical Cam WB RGB correction: 88, 157, 238
    Sunny Day Physical Cam WB RGB correction: 242, 255, 250
    Rendered to Max VFB, saved as 16 bit TIFF at 2.2. No PhotoShop corrections except to add text and save as jpeg.
    Other settings shown in the images.

    Cloudy Day


    Sunny Day

  • #2
    I think the difference in the f-stop and color bleeding comes from the materials. Reducing the brightess of the materials accordingly will give you better results both with respect to the bleeding and the f-stop.

    Best regards,
    Vlado
    I only act like I know everything, Rogers.

    Comment


    • #3
      excellent work. Yes, as vlado mentioned, there was another post similiar to yours where the poster couldn't get the exact same values, and it appeared his materials were too bright. Yours are pretty darn close, as your images show.
      ____________________________________

      "Sometimes life leaves a hundred dollar bill on your dresser, and you don't realize until later that it's because it fu**ed you."

      Comment


      • #4
        yes pretty close...good test too. But, I would say that the sky color depends also on world positioning, day of month, year etc.
        The tests are pretty close too!..
        Dmitry Vinnik
        Silhouette Images Inc.
        ShowReel:
        https://www.youtube.com/watch?v=qxSJlvSwAhA
        https://www.linkedin.com/in/dmitry-v...-identity-name

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        • #5
          Here's the post I made previously on this subject back when the vray physical cam/sky model was just introduced:

          http://www.chaosgroup.com/forum/phpB...ic.php?t=16499

          Short answer, you will have to adjust material intensities down, even if you do use phys cam exposure. Because white 255,255,255 is not the color of a white object, it is the maximum brightness of the image.

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          • #6
            I don't know the math, but there's a way to sample a swatch in your color card, compare it against the swatch in the rendered example, and use the difference as the white balance value in the vray phys cam.

            Comment


            • #7
              These threads will help with that.

              http://www.chaosgroup.com/forum/phpB...=white+balance
              http://www.chaosgroup.com/forum/phpB...=white+balance

              Comment


              • #8
                also with the reference photos you shot having the camera set to auto white balance can mess things up if your trying to reproduce it.
                You need to fix the white balance on the camera then match it in the vray camera.
                Chris Jackson
                Shiftmedia
                www.shiftmedia.sydney

                Comment


                • #9
                  Originally posted by Dynedain
                  I don't know the math, but there's a way to sample a swatch in your color card, compare it against the swatch in the rendered example, and use the difference as the white balance value in the vray phys cam.
                  You are talking about a color profile?

                  I added some month ago a wish to the wishlist and still think it's a valid and usefull wish: to apply a colorprofile of defined colorspace or different real rollfilms to the renderoutput or embed colorprofiles to the renderoutput to enable working in photoshop in a defined colorspace.
                  www.cgtechniques.com | http://www.hdrlabs.com - home of hdri knowledge

                  Comment


                  • #10
                    Very nice test indeed.

                    I don't know how to achieve a correct overcast illumination. Is it correct to set size multiplier to 1000 to get an overcast illumination?
                    I've done a some quick tests and seems that setting sun size multiplier beyond a certain value (213?) suddenly get the same results than disabling the Vray sun ... seems weird to me.

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                    • #11
                      I did something awhile back where I needed to get less sun and I put a diffuser type thing infront of the sun. Kinda like approximating a cloud.
                      ____________________________________

                      "Sometimes life leaves a hundred dollar bill on your dresser, and you don't realize until later that it's because it fu**ed you."

                      Comment


                      • #12
                        HDR's are nice and easy
                        Chris Jackson
                        Shiftmedia
                        www.shiftmedia.sydney

                        Comment


                        • #13
                          Thanks all for the replies. I will re-shoot the photos using a different white balance, perhaps doing a real white balance on the white material? I will also try reducing the material's brightness as well as following the other suggestions posted here and repost when tests are complete.

                          Craig

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                          • #14
                            you should write a comprehensive tutorial with what you've just done. I'm sure it would become VERY popular.
                            ____________________________________

                            "Sometimes life leaves a hundred dollar bill on your dresser, and you don't realize until later that it's because it fu**ed you."

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                            • #15
                              Sure. I'd be glad to if there is interest.

                              Craig

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