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slide projector - is this a bug or is this normal?

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  • slide projector - is this a bug or is this normal?

    sometimes i need to throw an image as if it is projected from a "slide prjector" (remember those?) or a digital projector, because i want to see shadows obstructing the image etc (so i can't just make the receiving surface emissive).

    this worked fine in 1.05 as follows:
    -build a box with one side missing, insert a point light
    -build a "slide" for the missing side. diffuse layer = transparent (or remove), refraction layer IOR=1.0 and insert image into transparency slot

    in the current 1.50.22564 release, the image has to be inverted, no problem. however it also always comes out desaturated - it has the wrong gamma. (the image can also be placed in the refraction color without being inverted, but the same desaturation problem happens)

    i'm working in a gamma corrected workspace (not linear workflow), so my color mapping looks like this:
    gamma = 2.2
    input gamma = 2.2
    linear workflow = off
    Correct LDR textures = on
    Correct RGB colors = on

    with these settings, most image maps look correct, but the "slide projection" always looks desaturated, as if Correct LDR and Correct RGB are turned off for those images.

    I can fix this by changing the color space in the slide texture (inside refraction transparency) to sRGB, or by changing the gamma to 0.494949 - that is, by manually correcting the gamma.

    so i have a workaround, but I'm wondering if this is the expected performance of the refraction transparency (or refraction color), or if this is a bug? it seems weird that this is the only place i have to manually correct gamma.


    here's the image used as the "slide":

    Click image for larger version

Name:	slide1.jpg
Views:	1
Size:	8.2 KB
ID:	878721

    here is the render with uncorrected gamma:
    Click image for larger version

Name:	Gamma 1.0.jpg
Views:	1
Size:	16.7 KB
ID:	878722

    here is the render with manually corrected gamma (you can see it matches the original image much better):
    Click image for larger version

Name:	sRGB.jpg
Views:	1
Size:	15.6 KB
ID:	878723


    thanks!
    Last edited by fooprobe; 18-10-2013, 11:33 AM.
    emil mertzel
    vray4rhinoWiki

    Lookinglass Architecture and Design

  • #2
    thats my work around as well changing the gama to 0.5 thanks for the srgb trick I didnt know about that.
    this has been bugging me since the realease of 1.5
    check my old post
    (Okay thanks Micha... I think I found a wourkaround.. but this seem bizarre to me..
    I bring down the gamma correction value in the bitmap and then increase the multiplier to get contrast..
    Its logical but seem very time consuming...)

    http://forums.chaosgroup.com/showthr...light=swisscad

    Comment


    • #3
      I can tell u one thing it hasnt changed in 2.0

      Comment


      • #4
        That's disappointing. Thanks for the info though.
        emil mertzel
        vray4rhinoWiki

        Lookinglass Architecture and Design

        Comment


        • #5
          And interestingly, I'm denied access to the link you posted! What forum did you post in, I'll search.
          emil mertzel
          vray4rhinoWiki

          Lookinglass Architecture and Design

          Comment


          • #6
            yes the thread is from the beta testing from 1.4 to 1.5 sorry i thought it was open
            anyway it not fixed and as I understand it it wont be fixed or changed..


            /
            Quote Originally Posted by fpedrogo View Post
            Hi
            Well in the old build 1.05.29 we use to correct the gamma for the environment. We are not correcting the gamma for the environment anymore. You can find more info in the migration section on Spot3d.com
            http://www.spot3d.com/vray/help/rhin...ate_to_1_5.htm

            Best/


            Okay this will not be corrected...
            HDRI and V-Ray Sky gamma

            In V-Ray 1.05.29 there was a bug that caused HDRI and V-Ray TexSky to have the incorrect gamma result. We no longer apply the inverse the gamma to and HDRI or TexSky because they have their own gamma value of 1.0. This could affect your final rendering. To get the same result as in V-Ray 1.05.29 you will have to correct the gamma for the HDRI in the V-Ray texture editor. We don’t have a way to correct the TexSky gamma.

            Comment


            • #7
              Hi
              If you are using an emissive layer, you will have to change the "Color space" for the image to sRGB or you can manually invert the gamma of the image. Assuming that the baked image gamma is 2.2, you can type .4545. Seem that the emissive material do not correct the gamma of the texture.
              If you are not using an emissive layer, you should not get any issue. We correct the gamma on the refraction color and on the transparency slot.
              Here is my test using sRGB as color space for the emissive image.

              Click image for larger version

Name:	emissive_gamma_sRGB.jpg
Views:	1
Size:	19.8 KB
ID:	851069

              Comment


              • #8
                Thanks, Fernando - but I had this problem in the refraction layer, with no emissive layer. I haven't had a chance to check with the latest release, but swisscad says it hasn't been fixed. It would be great if this could be fixed, otherwise it's very confusing because "correct LDR" is supposed to correct LDR, right?
                emil mertzel
                vray4rhinoWiki

                Lookinglass Architecture and Design

                Comment


                • #9
                  Thanks, Fernando - but I had this problem in the refraction layer, with no emissive layer. I haven't had a chance to check with the latest release, but swisscad says it hasn't been fixed. It would be great if this could be fixed, otherwise it's very confusing because "correct LDR" is supposed to correct LDR, right?
                  Hi Emil
                  Yes, I'm able to reproduce the issue. I was using linear workflow and we don't have any issue with that tool. The issue is with "Correct LDR textures" gamma correction tool.

                  Thanks

                  Comment


                  • #10
                    Great - hope it can be fixed! Thanks!
                    emil mertzel
                    vray4rhinoWiki

                    Lookinglass Architecture and Design

                    Comment


                    • #11
                      Just a quick update for this gamma issue. We just fixed it. It will be out soon.

                      Comment


                      • #12
                        Thanks, Fernando!
                        emil mertzel
                        vray4rhinoWiki

                        Lookinglass Architecture and Design

                        Comment


                        • #13
                          Not fixed yet. See case (10339). Please don't forget.
                          www.simulacrum.de ... visualization for designer and architects

                          Comment


                          • #14
                            Not fixed yet. See case (10339). Please don't forget.
                            Hi Micha
                            The problem here is the gamma on refraction layer. We fixed that issue.
                            The gamma issue with the emissive layer still there. The only solution right now is change the gamma mode to sRGB.

                            Comment


                            • #15
                              My quick workaround is to set the gamma of the emissive layer at .45. So I can keep the corrected workflow. But I hope a fix is possible, there shouldn't be special solutions, because over the years it will be more and more and new users are confused.
                              www.simulacrum.de ... visualization for designer and architects

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