Problems with linear workflow

[Alyosha]

Hey guys...I've attempted to learn linear workflow, and while everything is pretty clear there are these wierd anomalies that show on renders...jagged edges and random black artifacts appear when using linear color mapping and unchecked "clamp"...

 

anyone has any ideas? I'm attaching the render...check the water in the tub for example and window shelf. It is unedited pic so exposure is totally off, but that doesnt matter, what bothers me is the black outlines? artifacts...

 

[ATTACH=CONFIG]41369[/ATTACH]

[Ismael]

"It is unedited pic so exposure is totally off, but that doesnt matter,..."

 

That is the problem you are having. Exposure has to be taken into account at rendertime and not at post..., within reason. Your camera is "blinded by the light".

[Ismael]

From the book “Real World Camera Raw with Adobe Photoshop CS4

By Bruce Fraser, Jeff Schewe

“As with white balance adjustments, exposure adjustments performed as part of the raw conversion are relatively lossless (unless you clip highlights to white or shadows to black), unlike tonal adjustments made in Photoshop on the rendered image (see Figure 1-3). In practice, however, you have less freedom to adjust exposure than you do white balance.

The main limitation on exposure adjustments is that when you try to open up significantly underexposed images, you’ll probably see noise or posterization in the midtones and shadows. It’s not that the edit is destructive—you just didn’t capture enough shadow information in the first place.

Completely blown highlights are also beyond recovery, but camera Raw goes a good bit further than other raw converters in rescuing highlight detail even when only one channel contains data. Depending on the camera and the white balance chosen, you may be able to recover one or more stops of hightlight detail. Nevertheless, good exposure is still highly desirable---see the section “Exposure and Linear Capture”, earlier in this chapter.”

[Stephen Thomas]

This isn't really a linear workflow problem. I think the problem you are having is more to do with how to use the Vray sun and physical camera. You should also use vray plane lights at your window if you aren't already. This will give you more fill light allowing you to lower the sun exposure and create a better balance. At the moment there is too much contrast between your direct light and GI, which is why you are getting the artifacts.

[Alyosha]

Hey, thanks for the reply!

 

 

So basically the black artefacts and outlines are a result of too high exposure?

 

How come that using exponential mapping didnt produce such artefacts though, at exactley the same exposure setting for the camera? Probably because it incorporates some sort of exposure control in itself?

 

Thanks buddy, that is great information:-)

[Alyosha]

yeah stef I'm aware of that problem in the scene, I do have portals in windows at all times...thanks guys you've been really helpful and you pinned the problem for me:-)

 

lowering overall exposure and bringing out the light in post-prod hdr file did the trick for me!

 

I like to obtain very contrasty renders personally, where light is on the brink of being overblown, with a lot of contrast with the dark areas...so i tend to seek such camera solutions as well...

 

maybe i should find another way:-)

[Ismael]

"maybe i should find another way:-) "

I think that you are 'finding', even as we speak...

Best regards.

[Nic H]

the problem here is unclamped is unchecked - if you want to do this (do you really need to do this?) you need to up your antialiasing significantly to something like (deep breath...) 1/100 - 0.0025 to have enough sampling to clear up the aliased areas

 

i would just check clamping on to be honest - you aren't going to be making use of the full unclamped range anyway imo.

or switch to reinhard and lower the burn value. if your renders are too bright and not contrasty enough i reckon you have too much light in the scene or your materials are just far too bright value/rgb wise

 

I think im on teh right path here ? - i always leave clamped checked these days, other than a few tests that took ages years ago i ahve seen no reason in the type of work we do to use unclamped.

[Alyosha]

Yeah you are...the training I followed for the linear workflow suggested clam is unchecked. Thanks!

[Crazy Homeless Guy]

I think im on teh right path here ? - i always leave clamped checked these days, other than a few tests that took ages years ago i ahve seen no reason in the type of work we do to use unclamped.

 

+1.

 

I used to try and work linearly, but now I subscribe to the K.I.S.S. philosophy.

 

Keep It Simple Stupid

 

And my humble rant to try and explain...

 

It is important to do some correction, but I think the whole everything must be linear workflow thing has hurt visualization more than it helped. Sure, maybe it keeps some colors in check and a few other things, but for me at the end of the day it comes down to aesthetics, and not some math formula.

 

Anyway, ...I mostly use Reinhard set to about .8, I always clamp, I always sub pixel map. I also use a 1.8 gamma, with a 2.2 correction on textures, and 0.818 on output.

 

I also only use camera exposure half of the time, and rarely use the white point balance. On a day to day basis I don't see why it is necessary to throw extra things into the mix that you are going to need to turn around and do something else to correct moments later?

 

Meaning, why use a physical sun that is so bright? This means you need to place exposure on your camera which creates extra steps in the process. It also means you photometric lights are going to be difficult to adjust, and require a lot of trial and error. Which means you will have to spend even more time balancing what you are doing because you want to live in a 'physically correct world.'

 

To tell the truth, I typically just use a direct light or a spot cone for my sun in combination with a Vray sky that has a color correction modifier placed on it. It gives me immense control of the scene down to every last detail and does not leave me at the mercy of physical exposure on a camera.

 

At the end of the day what we do is primarily make an aesthetic image, so really, not settings are wrong as long as it looks good. Or at least decent. That is what we are paid to do.

 

If we were doing daylight analysis, then yes, we would need to work with real world numbers. But we are not, or at least I am not.

 

Alright, I will stop ranting, but I will say one more thing.

 

In photography we often gravitate towards images where the light looks mystical, unreal, or special. ...but in rendering we try to make like look like it would on a normal day? It kind of makes you scratch your head.

[Alyosha]

Thank you for your elaborate opinion.

 

 

Why I choose to work with vray sun and physical camera?

 

Because thats exactley what I'd like to achieve - natural and flowing light distribution. I make it a point to try and avoid "cheating" and instead attempt to achieve results in a "physical" manner at all costs.

 

imo only when you perfect this approach you can go a step further and make mystical, unreal or special renders as well that are on par with actual real life photographs.

 

It is my passion and the way I like to do things in 3d, and I like to go past the what is required to do a job.

 

 

If I had a small render farm I'd prolly switch to maxwell or indigo in the blink of an eye:-)

[luisoosiul]

It is important to do some correction, but I think the whole everything must be linear workflow thing has hurt visualization more than it helped.

 

Are you joking? LWF is the easiest way to work, because is the correct way to work. The problem is that the people learned to make fakes in their render to obtain esthetic results and now is easiest fo them to continue working making fakes than to change the chip and learn a new workflow. But i think that is more easy for a begginer to learn LWF than to learn to do all fakes necessary to obtain a good image working in an 2.2 gamma visualization space.

 

I think the problem of the image is not de LWF. The problem is that que sun is very much bright respect the usual lamps. And the problem for the vray is that it has problems working with intensity values higher than 255. The brighter areas of the image have float intensity values very higher to 255 near of normal intensity values and vray have a lot of problems to calculate the antialiasing in that areas, unless the settings of the antiliasing are very high. Then you obtain this blacks artifacs and long calculations times. You can check clamp option to resolve the problem, but this involve more time to render, and you lost all the extra light information for the postproduction process. You can also to fake the sun intensity to try simulate how the human eyes works, and work with skyportals lights to compensate it. Or you can take two diferent expositions and blend it in postproduction. There is a lot of ways. To gave up the LWF is not the best.

Cheers.

[Crazy Homeless Guy]

Are you joking? LWF is the easiest way to work, because is the correct way to work. The problem is that the people learned to make fakes in their render to obtain esthetic results...

 

You can check clamp option to resolve the problem, but this involve more time to render, and you lost all the extra light information for the postproduction process. You can also to fake the sun intensity to try simulate how the human eyes works, and work with skyportals lights to compensate it. Or you can take two diferent expositions and blend it in postproduction. There is a lot of ways. To gave up the LWF is not the best.

Cheers.

 

No, I am not joking.

 

The 2.2 adjustment is a gamma correction that comes close to simulating linear light, but I don't consider it to be the be all end all to rendering and visualization. At the end of the day you need to trust your eye and mind, because if it does not look right aesthetically, then it more than likely is not going to suffice in day to day work.

 

I tend to work between a 1.5 gamma space to a 2.2 depending on the scene I am creating, and the mood I want, how much contrast, and what are the important elements. I work in a gamma adjusted space, but I am interested in making the gamma for me, and not me work for the gamma.

 

Bottom line, there are several tricks that you are going to use to get you pixels to look right on the screen. Some include clamping, or blending colors, others are working with gamma in different ways.

 

But in the end, if it does not visually engage the user, then it is not a good piece, and it doesn't matter if it was rendered in a gamma correct space, or not. It is about how well it communicated the story and information that it was intended to communicate.

Edited March 17, 2011 by Crazy Homeless Guy