Proper Comping Etiquette

[MoonDoggie]

Hello,
Trying to wrap my head around simple comping and I'm having some difficulties, so to illustrate I've included a sample scene, my setup, and some renders, to aid me/you.

Here is the desired result when comping the background (base pass) with the overlayed sphere pass



Here is the base pass rendered completely normal, just hiding the sphere



Here are the VrayProperties for everything except the sphere, and the Background Environment is set to black



And here is the resulting sphere pass,



White is actually alpha

[Continued to next post, because I can't post 5 images in the same thread]


-Colin

[MoonDoggie]

Here is the resulting image from photoshop when comping together the base pass and the sphere pass



For some reason the result is much darker than the normal render. Also the reflection is not visible in the floor. How can I achieve the same result? Thanks for taking the time to read this.

-Colin

Here is the max file

http://www.colinsenner.com/personal/CompTest.max

[instinct]

well the sphere is a lot darker in the render before comp. why did you set the environment to black ? as that will darken the sphere wont it ?

Regards,
Thorsten

[MoonDoggie]

The environment was set to black I thought to properly pre-multiply the background with the alpha, is this incorrect?

-Update: Changing the bg to white gets it closer to the final desired image, however, it seems a bit dark still, and there is no reflection in the floor.

[instinct]

Well no that is correct. But if the environment was also your reflective/GI environment then you need to use the overrides to get the same results. Looking at the sphere alone render it is already a whole lot darker then in the scene. So it seems that is the case.

Regards,
Thorsten

[MoonDoggie]

well it's pretty close, not exact, but close to the same, without any reflection on the floor, though the color bleed is starting to show up on the walls

[MoonDoggie]

Here is the result with a white override sphere comped onto the base pass



And the desired result for comparison

[instinct]

okay. The next question would be if that was LWF and what fileformat you used. Cause all the comping is supposed to be done in Linear space. At least that got rid of a lot of troubles for us.

Kind Regards,
Thorsten

[MoonDoggie]

Thorsten, by the way, thank you already for all your input.

These are not done in LWF, the base render was output for forum reasons as a jpg, the overlay pass was done as a png with alpha saved.

[MoonDoggie]

Also if you look on the right window frame there is some reflection missing from the ball like is in the original image, how can I bake in reflection so I can overlay it onto the base pass?

[instinct]

np at all. I just couldnt try playing with your file earlier. I dont have Max2k8 tho (i assume it is a 2k8 file as it doenst open in R9 here). I tried to do something similar at least :

The first one is the straight vray render. The second one is the PS comped one. PS is really a tad bitchy and there still is a slight difference around the sphere edges. That's prolly due to premultiplication issues or PS's incredibly stupid way of handling png's with alpha. Rest assured that it might be just me as i hardly ever use PS. The color matches nicely tho. I also uploaded the 3 max files i used to do it. It's rendered to png as you did tho i would recommend writing to linear EXRs instead if you plan doing this kinda post.




http://www.instinct-vfx.de/temp/compexample.zip

Kind Regards,
Thorsten

[instinct]

I missed your post while writing mine :P All i did is set the sphere's "Visible to camera" property in the max object properties to off. That keeps reflections in there and casts correct shadows.

Regards,
Thorsten

[MoonDoggie]

Excellent! let me play with this a bit. When you are rendering linearly, are you changing the gamma value of 3dsmax and your colormapping to 2.2? or just setting the gamma when you save the file in openexr?

Also, what if I need the red sphere's reflection to actually be baked into the overlay instead of baking it into the base render? Is this easily possible without going to comping solutions with VRay Render Elements?

[instinct]

Well to render linear i simply set the Gamma/LUT in the prefs to 2.2 set the input gamma to 2.2 and check "Affect Color selectors" and "Affect Material Editor"

When now rendering to exr's directly via the VRay VFB they are linear. Only thing to keep in mind is that you should change the gamme to 2.2 in the colormapping rollout and tick "Dont affect colors". If you dont then the sampler will do it's importance sampling in sRGB wich usually results in pretty harsh undersampling in lwf. To preview the final image simply check the "display colors in sRGB" button in the vfb and you're set.

To bake the reflection with the reflection pass you would leave the visible to camera on for the room and make it a matte object but leave the reflection and refraction amount at 1. Then only reflections and refractions are overlayed.

Regards,
Thorsten

[MoonDoggie]

perhaps you can illustrate a baked reflection with the overlay. Here is what I'm doing to no avail.

setting the entire room (except the sphere) to matte object true, alpha contrib: -1, shadows on, affect alpha: on.

then setting the sphere to visible to camera, matteobject false, alpha contrib 1.

But as illustrated in my above renders, this doesn't include the reflection of the sphere in the floor.