Linear workflow correct in VfSU?

[kwistenbiebel1]

Hi all,

I was wondering the other day if the linear workflow is behaving correctly in Vray for Sketchup.
Why? Because most renderings look kind of washed out, even when applying the right gammacorrection parameters in the global switches panel (input 2.2, output 2.2, correct RGB and LDR checked).

This is not a hugh problem as it can be corrected in photoshop or by using the tonemapper (level correction etc...)but still some aspects on the postprocessed images look odd. For instance, areas with bright refl./speculars get clipped to white etc...
For some reason I have the feeling that the linear workflow is off.
Maybe due to how Sketchup handles gamma control?

Could someone of Asgvis give an insight on this?

By the way, the textures I use look 'right' on input (=not washed out), meaning they have
a gamma correction baked in to obtain a realistic appearance on a 2.2 monitor.


Cheers,
Biebel

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

I did a test and clearly something is odd.

In the first image I use the default textures (which appear realistic in photoshop).
In the global settings the needed 'global corrections' are checked.

OUTPUT 1:


The brick texture used:


In the following image I did a manual gamma correction per texture instead of using Vrays global correction.
In order to do this, I opened each texture in photoshop and altered the gamma manually (they appear much darker).
In the global settings panel I assured that the 'correct LDR' is checked off, avoiding a double correction.

OUTPUT 2:


The brick texture used:



Clearly, the resulting image is not at all the same as the previous. Textures have a better contrast, while in the first image they look washed out. This is very noticeable when you look at the brick texture.

Conclusion: Does the 'correct LDR' option in VrayforSketchup work correctly?......Not sure.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

As a reference I post a rendering made with Podium.

I used the first brick texture (see post above) and the bricks comes out sharper and much more detailed.
I would like to have the same crisp looking brick in Vray....How can I do that without having to gamma correct the textures manually?

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

Ok...It seems that the linear workflow thing was not the problem here ....

I just found out that the textures come out flat because of a LINKING MATERIALS BUG !!!
It seems that the linked brick material consists of a blend of the texture and a seperate solid beige color. This causes the lack of detail in textures on the output.

I removed the linked brick material and instead built up a new vraymat for it. This solves the problem.The brick detailing is back.

By the way, where is that updated version of VfSU?
It would be great to have a version that works without the nasty workarounds.

Brick texture fixed:

[dalomar_cg]

Re: Linear workflow correct in VfSU?

It seams you've done quite a bit of testing here...Out of the box, V-Ray is setup for linear workflow. Meaning that the output is gamma corrected for display on monitors with a gamma of 2.2, and that the LDR Textures and any colors have an inverse gamma correction so that they appear normally in the final gamma corrected image.

Personally, to counteract the tendency for textures to get washed out, I actually have a higher gamma value for the inputs (textures and colors) then the output (at 2.4-6 and 2.2 respectively). What this does is "over corrects" the inputs making them have slightly darker mids, and a little oversaturated. The end result in the output is that the input colors have less tendency to be flat.

As far as some of you're tests, the one with the manually corrected textures looks "right" in my eyes, so thats something that will have to take a look into. In the SR we are going to be changing how we deal with materials, so you'll be making fewer linked materials then before, but either way I'll bring it to Joe's attention.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

Thanks for that reply Dalomar.
I am really looking forward to the updated version.
It was surprising to me to see a difference in the earlier images I posted as I expected the first and the second to be similar.
Maybe I should try this test again with vraymats instead of linked mats.

Cheers and good luck with the upcoming SR release,
Biebel

(Ps: Don't forget to include working clipmaps that hold the position of the SU diffuse counterpart . For the moment that is a thing I miss a lot (treelines, trees, etc..))

[dalomar_cg]

Re: Linear workflow correct in VfSU?

(Ps: Don't forget to include working clipmaps that hold the position of the SU diffuse counterpart . For the moment that is a thing I miss a lot (treelines, trees, etc..))

Don't worry, the material changes make things a whole lot better, and a whole lot easier. The clip mapping stuff is taken care of. Viewport feedback is greatly improved, and mapping is much less of a hassle (on the v-ray side). We'll get things out as soon as we can...hopefully you guys will think that it is worth the wait.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

Yummie ! that sounds good.

[mirolator]

Re: Linear workflow correct in VfSU?

Biebel,

That's interesting. When I first started using VFSU, I had the same problem of a blended material being washed out. It was frustrating, and to be honest, I'm not sure how I fixed it. I think I ended up removing, then re-applying the material. Thanks for the great insight.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

.... The clip mapping stuff is taken care of.

Just to inform you I finally got the clipmaps working. Even with the Sketchup uv's applied

This is the workflow:
1. apply the texture you want to see clipped to a surface in SU.(both sides!)
2. See to it that those surfaces (including their edges) are all exploded.
3. Do NOT make a Vraylinked material. Instead make a Vraymat and assign the clipmap texture (the area that needs clipping has to be white, the visible part full black)in the transparency slot (= the one next to the diffuse slot).
4. Select the faces and their edges. Context click and choose 'assign Vraymaterial' and choose the Vraymat you just made out of the list.

HIT RENDER...It works !!


Note: Unfortunately the faces can't be nested in components and/or groups.
So you need to explode the geometry at the fullest.
No problem for simple surfaces but a big problem if you want to use clipmap leaves on complex 3D trees (like Xfrog). Those trees are composed of nested components (leaves, branches, trunk, etc...). Exploding those trees will 100% sure Crash your Sketchup session. (Exploding hi poly objects is a pain in SU).

I just liked to add this so maybe the developers make clipmap functionality possible for nested geometry also.....

Cheers,

By the way...I'll try to post an example later of successfull clip mapping.

[jenujacob]

Re: Linear workflow correct in VfSU?

thanx chirs.. will try it out!

[rv1974]

Re: Linear workflow correct in VfSU?

Hi Biebel!
Really well done,lucky your friend.Could you
be so kind to post your typical postwork cure against washed off output? Levels, curves...?
Thanks in advance.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

Thanks!

About correcting washed out images:

A simple tool to correct in photoshop is the 'levels' option. Often it helps to slide the outward arrows closer to the curve (it's called 'histogram).
Another hany tool is 'curves': making an S- shape enlarges the contrast on both highlights as shadows.
Another cool way of fixing the washed out appearance is copying the image layer and applying different 'blend modes' to those copied layers. For instance 'screen' to brighten things up and 'soft light' to increase the contrast in light (and color).

There are several good photoshop tutorials out there on the net that handle this subject.


By the way,
I was browsing the Vray for C4D (Cinema4d) gallery and it struck me how much more contrast is present in most of the images posted there.(also in exterior scenes)
That makes me think that neither we aren't good renderguys over here ;D or indeed there is something off with the default linear workflow in the VrayforSketchup version.
Or is it because of a different implementation of the Vraysun?....

Maybe Dev team could shine a light on this....?

[dalomar_cg]

Re: Linear workflow correct in VfSU?

There are levels and curves control within the framebuffer, so you don't have to do them in Photoshop if you don't want to. In fact, its better to do them within the framebuffer because the corrections will be done off of the float data as opposed to the 8-bit data, which will prevent gaps in the histogram and more flexible info (ie colors beyond 1).

http://www.spot3d.com/vray/help/150R...x.html#toolbar

There isn't anything off with our linear workflow. When we initially went back and changed the way that was structured, I went through and worked out the kinks with how we corrected the inputs (everything else is using V-ray core stuff, so is the same in all V-Ray engines). It it was off, we would have found it a while ago.

It is entirely possible that there might be an issue with the translation of the maps from linked materials, but thats about it (I still have to get to testing that one).

As far as non gamma corrected images in general, they will have a tendency to look more contrast full because the darks will be darker, and there will be a quicker change from darker to lighter colors. Whether the C4D images are gamma corrected or not, I don't know.

I do remember stumbling on the sun acting a little weird, which was really hard to pin down on the exact cause of the issue. Vlado also changed some things with how the V-Ray sun worked (internally), and I think that was like mid summer, so that wouldn't have made it into the released version of VfSU. It is looking better in the development builds that I've been working with, so hopefully you'll see a change when we release the beta of the new SR.

[kwistenbiebel1]

Re: Linear workflow correct in VfSU?

Thank you Damien for that explanation.It is reassuring.

VfC4D uses the newer vray 1.5 engine
Is this new engine going to be part of the upcoming service release of VfSU as well?

I believe one of the most important things to prevent washed out images would be a correct use of the physical camera. For instance, increasing the ISO value increases the color/light contrast in classic photography so I presume this counts for Vray as well.
Any other tips you can give us to obtain a better light balance besides the tonemapper window?

cheers,
Biebel