adding vsun and vsky is not same render as sun and sky renderred together.

[giraffe]

hi,
I made a scene with vraysky and vraysun and vraycamera.
vraysky is in max environment (8 )

then I rendered sun and sky seperately and made different passes.
for skyonly: I disabled sun
for sunonly: I turned on GI environment skylight with black color and 0.001 multiplier

then I made another render with both enabled.

when I add the sunonly+skyonly in photoshop (with liear dodge OR screen ), I get different result than sun+sky pass.

but when I do this with ANY other light, I get same results.
why is this?

[vlado]

Can you show the differences?

Best regards,
Vlado

[giraffe]

ok here are some renders:

all rendered to vfb. gamma is 2.2 (in color mapping section)
subpixel mapping is enabled. affect background is enabled.
vraycamera with default values. exposure and vignetting is on.



sun+sky pass:




sun.only pass:




sky.only pass




adding passes in photoshop (screen mode)

[giraffe]

doesnot let me put the 5th image in same post.
so here is the one with LINEAR DODGE

adding passes in photoshop (linear dodge)

[vlado]

When you plan to add any render elements or passes, make sure you don't have any gamma correction applied to them. You can apply the gamma only after you have done all the compositing (adding, multiplying or whatever).

There is an interesting page here to show how the compositing application can produce wrong results if gamma is not treated properly:
http://www.4p8.com/eric.brasseur/gamma.html

Best regards,
Vlado

[giraffe]

thanks for answer
you are right.

I made gamma=1
and did same renders.
now the lineardodged.layers and the default render are identical except background.

[giraffe]

now I have another question.
if we want to add these layers post, we need to render with gamma=1
so is it problem to save them exr?
because exr automatically puts 2.2gamma.
and it will put on these passes too.

[rivoli]

because exr automatically puts 2.2gamma.

actually it doesn't. exr it's a linear format with gamma 1.0, it will appear double correct only if you render with gamma 2,2 (without telling vray to do adaptation only). but it shouldn't be a problem anyway, rendering to a full float format you can change gamma later in post if you have to.

[vlado]

The .exr files typically do not contain any gamma correction (unless you enabled the 3ds Max Output gamma in the Preferences), so if you tell V-Ray not to apply gamma either, it should be fine.

Note however that by default many post-processing applications will either display .exr files with 2.2 gamma, or actually modify them in this way when they are read from disk.

Best regards,
Vlado

[giraffe]

oh I understand reason now.
because whenever I save in exr and open in photoshop, I see that 2.2gamma is applied.
so according your words, this is because how photoshop displays.