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Thread: HDRI Exposure Control ?

  1. #1

    HDRI Exposure Control ?

    Im using some of the free HDRI images from HDRI Haven - if you havnt found them yet, I highly reccomend you do.

    I have the HDRI image set as my backdrop using the Textured Environment function. It all works great, except sometimes by default exposure isnt quite right - sometimes things are a bit too bright.

    Is there a way to easily adjust the exposure of HDRI images being used to light a scene? All I can find under the Image Editor tab is the editing sliders which dont do what Im looking for, and then under the Processing tab there is "Exposer" and "HDR exposure" filters but these seem rather complex and I honestly cant figure out how to use them. They have black point and white point controls which dont seem to function as I had expected, I really just want to find a simple "expose up" or "expose down" slider or input.

    Any help or pointers would be greatly appreciated
    Last edited by scott.newman.ct; 09-10-2019 at 11:56 PM.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  2. #2
    A.K.A "The Silver Fox" Gungho3D's Avatar
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    Hey Scott - I'm digging into my "archives" here as these days mostly I'm using Octane, but here goes ...

    I have previously just messed with the gamma slider in the image editor (rarely needing to touch the other sliders), ignoring what the environment looked like (it wouldn't be in the final render anyway) but paying real close attention to the way it was "lighting" objects in the scene. Of course this all has to work hand in hand with global illumination settings, as messing with the HDRI's gamma affects the whole scene.

    If I did want a portion of the HDRI env to feature in my final render as part of the background, if I couldn't get it to look ok in the render itself (even though it was lighting objects nicely) then I'd to a second pass with objects removed and with the HDRI's gamma adjusted as required. Either that or push/pull the background into shape in post.

    I did the above for years until I got better at creating my own HDRI's ...

    Hope something in the above is helpful

  3. #3
    Thanks Gungho3D - Ive actually done that exact same thing myself for years. And then I try and offset the colour effects of messing with the gamma by playing with the saturation slider. It does kind of work as youve pointed out, but Ive always felt that this is kind of winging it and its not really the proper approach.

    One thing Ive found that works quite well is just having one environment light in the scene with sample backdrop on. Then adjusting the brightness of that light seems to adjust the exposure of the HDRI image on your objects. It works quite well, and the result looks good in preview but then at render time its almost un-usable because there are so many fireflies in the highlights. Ive tried adjusting all the different samples and camera samples to get rid of them, with no luck.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  4. #4
    A.K.A "The Silver Fox" Gungho3D's Avatar
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    Quote Originally Posted by scott.newman.ct View Post
    Thanks Gungho3D - Ive actually done that exact same thing myself for years. And then I try and offset the colour effects of messing with the gamma by playing with the saturation slider. It does kind of work as youve pointed out, but Ive always felt that this is kind of winging it and its not really the proper approach.

    One thing Ive found that works quite well is just having one environment light in the scene with sample backdrop on. Then adjusting the brightness of that light seems to adjust the exposure of the HDRI image on your objects. It works quite well, and the result looks good in preview but then at render time its almost un-usable because there are so many fireflies in the highlights. Ive tried adjusting all the different samples and camera samples to get rid of them, with no luck.
    I know exactly what you mean about fiddling with magic sliders until close enough becomes good enough - been loving Octane, it does have a learning curve, but not major.

    I noticed there were much less fireflies in LW-2015, but haven't messed with the native renderer in either LW-20119.

    PS love your aircraft work. I get to work on a lot of individual aircraft renders but not at your level of animating - I would aspire to such heights ...

  5. #5
    "I get to work on a lot of individual aircraft renders" - That sounds interesting Gungho3D.

    What would that be for? What line of work are you in?
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  6. #6
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    You should'nt use the environment as the light source, you should use and Environment light, where you can control easily the exposure, and you will not get fireflies on glossy reflections.



    Regards
    English is not my native language so please be patient.

    Salvador Ureņa
    http://urenasalvador.wixsite.com/portfolio

  7. #7
    Asticles, thats a great video! Thanks - very helpful. The raytarace only "cheat" technique outlined in the video is really helpful and works incredibly well in the video example, but Im finding it changes the look of my material quite severely with metal/conductor material types.

    So after following the video - I see my firefly problem is indeed in the specular indirect channel. I think the reason the problem is harder to fix with conductors is because they arent really made up of much diffuse direct and indirect. Conductors seem to be all specular direct and indirect and it seems the indirect is quite important for the realism factor.

    Damn fireflies.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  8. #8
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    You may want to go to the Shading Model tab of your Conductor surfaces and uncheck "Glossy Reflections" and see if that helps.

    Alternately, you may want to also check your Render settings for your Reflection and Refraction samples and bump them up a bit if necessary.

    This is a simple cube with the chrome conductor preset, using an HDRI (from HDRI Haven) and a single environment light.

    Click image for larger version. 

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    Here are my render settings.

    Click image for larger version. 

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    And here are my environment light settings.

    Click image for larger version. 

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    In the scene, I only have the single environment light, a cube, and a null Shape (plane) acting as a shadow catcher.

    The HDRI is loaded in Textured Environment set to the Y axis. The texture is set to spherical on the Y axis, but I set the width to -1 (I'm not sure why, I picked it up in a tutorial and I've been doing it ever since).

    You can see that Sample Background is unchecked in the Render > GI tab, but checked in the environment light dialogue. I also cranked up the environment samples.

    I'm sure this scene is far more simplistic than the ones you are working on, but it was quick and easy, practically zero noise, and rendered in 35.9 seconds.

    If I'm re-hashing stuff you already knew or have already seen, my apologies.
    Last edited by RPSchmidt; 09-11-2019 at 08:46 AM.

  9. #9
    Thanks for the suggestion RPSchmidt - unchecking glossy reflections option is great for small areas or objects that are far away. Unfortunately with my object (a whole bare metal aircraft) being quite close to camera, I need all the subtle reflections and the realism that raytracing brings.

    One thing I have noticed is that some HDRI images are worse than others at generating fireflies. So far it seems to me like HDRIs with really bright hotspots (like the sun) seem to be worse off than overcast, evenly lit HDRIs. Also - the amount of roughness the metallic surface has seems to play a big part. The smoother, more mirror-like it is the less the problem occurs. But the more "blurred" the reflection gets, the worse the fireflies become.

    If only Lightwave didnt have the firefly issue, it would be incredible.

    For now I think the workaround in the video posted above by Asticles seems to be the best option. It does take away a small amount of realism, but its manageable and can be compensated for by boosting the lighting and adding a few custom "cheat lights" if needed to fake HDRI environment edge highlights.
    Last edited by scott.newman.ct; 09-11-2019 at 10:42 AM.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  10. #10
    Frequenter
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    I am probably pointing out something that you already tried but anyway: did you already try the despike option?
    https://docs.lightwave3d.com/lw2019/...Render-Despike

    BTW your aircraft/dogfight clips are amazing!!

  11. #11
    Quote Originally Posted by fishhead View Post
    I am probably pointing out something that you already tried but anyway: did you already try the despike option?
    https://docs.lightwave3d.com/lw2019/...Render-Despike

    BTW your aircraft/dogfight clips are amazing!!
    Thanks for the kind words fishhead!

    Actually no! I havnt given despike a try yet. I'll give it a go and see if it can save the day
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  12. #12
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    Quote Originally Posted by scott.newman.ct View Post
    Asticles, thats a great video! Thanks - very helpful. The raytarace only "cheat" technique outlined in the video is really helpful and works incredibly well in the video example, but Im finding it changes the look of my material quite severely with metal/conductor material types.

    So after following the video - I see my firefly problem is indeed in the specular indirect channel. I think the reason the problem is harder to fix with conductors is because they arent really made up of much diffuse direct and indirect. Conductors seem to be all specular direct and indirect and it seems the indirect is quite important for the realism factor.

    Damn fireflies.
    Hi Scott, Maybe there have been a misunderstanding.

    You should try to:

    A)Create an Environment light (and set the hdri in the Textured Environment options, at Effects pannel).

    B) Disable sample Backdrop in Render properties. This makes the Gi does not count the environment by itself. This is not a problem because you use direct lighting to create the environment lighting, using the environment light.

    C) Set Reflection and Refraction options in Shading model, inside the surface editor, to Raytrace only.
    This makes that refraction and refraction does not count the environment (removing the nasty fireflies) BUT don't worry, because they get the environment data from the Environment light, how?

    D) Enabling on the Environment light Affect Specular AND Visible to Camera. This gives you all the realism you need from the environment. Don't forget to increase the MIS Samples if you need more shadows resolution, and that Sample Backdrop is enabled.

    Regards
    Last edited by Asticles; 09-11-2019 at 11:02 AM.
    English is not my native language so please be patient.

    Salvador Ureņa
    http://urenasalvador.wixsite.com/portfolio

  13. #13
    Registered User
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    Quote Originally Posted by Asticles View Post
    Hi Scott, Maybe there have been a misunderstanding.

    You should try to:

    A)Create an Environment light (and set the hdri in the Textured Environment options, at Effects pannel).

    B) Disable sample Backdrop in Render properties. This makes the Gi does not count the environment by itself. This is not a problem because you use direct lighting to create the environment lighting, using the environment light.

    C) Set Reflection and Refraction options in Shading model, inside the surface editor, to Raytrace only.
    This makes that refraction and refraction does not count the environment (removing the nasty fireflies) BUT don't worry, because they get the environment data from the Environment light, how?

    D) Enabling on the Environment light Affect Specular AND Visible to Camera. This gives you all the realism you need from the environment. Don't forget to increase the MIS Samples if you need more shadows resolution, and that Sample Backdrop is enabled.

    Regards
    This was EXACTLY what I was going to write in my original reply, but then figured the video talked about all of those settings, so I opted instead to make a suggestion on something that might have been related (glossy reflections) and show an example using the settings pretty much as described in the quoted post above.

  14. #14
    Quote Originally Posted by Asticles View Post
    Hi Scott, Maybe there have been a misunderstanding.

    You should try to:

    A)Create an Environment light (and set the hdri in the Textured Environment options, at Effects pannel).

    B) Disable sample Backdrop in Render properties. This makes the Gi does not count the environment by itself. This is not a problem because you use direct lighting to create the environment lighting, using the environment light.

    C) Set Reflection and Refraction options in Shading model, inside the surface editor, to Raytrace only.
    This makes that refraction and refraction does not count the environment (removing the nasty fireflies) BUT don't worry, because they get the environment data from the Environment light, how?

    D) Enabling on the Environment light Affect Specular AND Visible to Camera. This gives you all the realism you need from the environment. Don't forget to increase the MIS Samples if you need more shadows resolution, and that Sample Backdrop is enabled.

    Regards
    Hi Asticles

    Steps A) through D) is exactly what I have tried. There is definitely a difference in the way the specular indirect channel looks for a conductor - at least on my side there is. Depending on the shape and angle of the object this can become a big drop in realism. I noticed on some surfaces the difference is hardly noticeable, but on others catching the light and environment at different angles there is a big change and loss of realism. I will try post some screen shots ASAP.
    Last edited by scott.newman.ct; 09-11-2019 at 11:34 AM.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

  15. #15
    @fishhead - Wow! The despike filter actually worked out really well. Its almost sorted out the problem completely and no need for changing the surface reflection type now. I just hope the de-spiking stays nice and even and constant for animations. Will have to run a test.

    I honestly cant begin to say how thankful I am for these forums. If it wasnt for the help of other Lightwavers on these forums I would have quit a long time ago.
    Scott

    Cape Town, South Africa
    http://www.youtube.com/user/independentvfx

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