Linear Workflow (Master Zap)

[dustinbrown]

Don’t get me wrong, I’m all for anything that makes my life easier, but isn’t the whole point of a NON-linear workflow (passes, layers, hdri, etc in post) so that if your client or producer or whoever says “make it brighter in that corner” you can turn that around far more quickly in post than you can by rendering another full beauty pass in 3d?

I know that was one helluva run-on sentence, but hopefully you get my meaning.

Am I misunderstanding what you mean by “linear workflow?”

-Dustin

[Piotr Kolus]

Yes, you misunderstood.

This podcast was about the benefits of (or rather the downsides of not) compositing in a linear light color space as opposed to a video gamma color space.

This has got nothing to do with linear vs. non-linear workflows.

Personally I liked this podcast a lot and I’m surprised there aren’t more comments or discussions in response to it.

I’m working on flame and see a lot of the issues mentioned, especially with blurs, CC and glows. Now all I need is to find out how to work around it on flame.

Wouldn’t mind Autodesk adding a little “lin” button to affected modules, layers in action or complete batch setups. Or even to the project settings.

[GalouM]

It’s times like this I wish fxpodcast was a video podcast. It’s sometimes difficult to grasp what they’re talking about without visual examples, unless you’re already well versed in this stuff. I don’t imagine their only target audience is people who already know this stuff, or it would be a bit like preaching to the choir (kind of pointless). They obviously want you to learn something. But if you want to educate people and bring them up to speed on some of these more esoteric concepts, you have to take a step back and explain things much more clearly.

Just because I don’t understand gamma all that well doesn’t make me a noob, and it doesn’t mean people like me aren’t a demographic worth reaching out to a bit more in these podcasts. I’m just a 3D guy who has definitely noticed that 3ds Max has a gamma setting, but has always been afraid to touch it due to a lack of understanding. I know I’m not alone. In fact, I’m probably not even in the minority.

I think Zap’s next blog post should be on how an end user artist, such as myself, who doesn’t really understand gamma all that well, should set things up. I mean…my monitor has a gamma, Photoshop apparently has a setting, 3ds Max has a gamma setting, and I think Adobe Gamma gets installed when you install Photoshop. Then you have Nvidia drivers with a gamma setting. It’s a bit daunting.

The Wikipedia article on gamma correction was equally confusing. Someone needs to make a mock-PSA video that talks about gamma 🙂

[Piotr Kolus]

It doesn’t take more then a quick google search or following the web links mentioned in the podcast to find lots of articles and discussions, including visual samples.

It’s not that hard 😉

[Ana wills]

@ares 28897 wrote:

Yes, you misunderstood.

This podcast was about the benefits of (or rather the downsides of not) compositing in a linear light color space as opposed to a video gamma color space.

This has got nothing to do with linear vs. non-linear workflows.

Personally I liked this podcast a lot and I’m surprised there aren’t more comments or discussions in response to it.

I’m working on flame and see a lot of the issues mentioned, especially with blurs, CC and glows. Now all I need is to find out how to work around it on flame.

Wouldn’t mind Autodesk adding a little “lin” button to affected modules, layers in action or complete batch setups. Or even to the project settings.

Totally agree, it would be good if someone that was a little smarter than myself could come up with a solid Linear-Light workflow for flame.

Is it as simple as getting the 3D dept. working in Linear-Light, us Flame people getting the graded footage and converting it to Linear-Light, comping the 3D then converting it back to the gamma-adjusted space for TV?? (This is for TVC workflow)

Or,

Can 3D work in a gamma-adjusted space and we convert it to Linear-Light space??

Any thoughts??

cb.

[Edmund Tee]

You don’t need lin button in Flame or any other software to do a math operation in linear light if you’re in 2.2 gamma encoded space. Just need to reduce the gamma to 0.4545 (1/2.2) before the critical operation and then get it back to 2.2 after the operation and you’re good. But yes it’ll be simpler if it we had this button or if all softwares were in linear light like in Nuke:rolleyes:.

[nigel]

Hey Chris

>Is it as simple as getting the 3D dept. working in Linear-Light, us Flame people getting the >graded footage and converting it to Linear-Light, comping the 3D then converting it back to >the gamma-adjusted space for TV?? (This is for TVC workflow)

>Can 3D work in a gamma-adjusted space and we convert it to Linear-Light space??

> Any thoughts??

You want 3d working in linear light with lin textures and lighitng with linear values, Maya colour swatches are gamma corrected by default. Depending on the renderer there are also issues with the way it resolves the final render. PRman does it nicely, Vray and Mental Ray leave a bit to be desired. You will wanna go to .exr and import linear exr in Flame. Its a through and through workflow. I discussed this quite a lot with some of the 3d guys there, wont say names on forums but you will know who I mean. In Nuke like the film guys use its a much easier process. In Flame so much of the tools are either gamma biased or not expressly developed for this kind of workflow that it is problematic.

Working linear is not just a matter of applying an inverse to the 2.2 gamma of sRGB images. It is a pipeline decision. There is the whole issue of float and what colour and compositing operations are appropriate for dealing with claues beyond 1. With boradcast there needs to be a decision made as to ingest and handling of footage. If you are coming infrom tape then you already have gamma corrected footage which only has 8-10 bits of YUV data. If you are geeting scans then you need to linearise these take you linear CG and then composite them in a fashion which will work appropraitely. Then you will need to be using viewer lookups to monitor your work as it will not display correctly on either the monitor or any kind of bradcast device. Again there are tools and workflows for all this but someone has to invest a little bit of time and energy in making it all work for your particular facility and needs.

I talked to Mike and the Fxguide guys last week abou tdoing a follow up podcast from a compositors persepctive. We had a few dealys because of scheduling but I am still hoping we can get it out there.

hopefully there can be more discussion on this soon,

cheers,

tahl.

[Ana wills]

Thanks for that Tahl!!

cb.

[Ana wills]

Hey Tahl, I hate to be the go between but Philippe gave this great response to my question of Linear-Light workflow in flame:

Conf: flame-news
From: Philippe Soeiro
Date: Friday, October 09, 2009 01:54 PM

Hi guys,

Sorry I missed the begining of this thread. I did not mean to ignore it!
It is true that as far as blending is concerned in Action, the maths actually assume linear sources! Incidentally this has forced us to create blending curves precisely to compensate for the fact that most users don’t actually use linear “scene referred” footage in Flame. If you look at the entire Flame toolset, things become a bit more blurry, but I suspect this is the case pretty much in every application.

If you take the example of a colour correction, it should assume an average grey at 0.18 with linear images as opposed to 0.5. This is something that Flame doesn’t do with the exception of the Exposure node. A gamma compensated image will shift a mid grey to 0.5 and it is a common assumption that this is how things should be treated in most applications. As stated before, this assumption is incorrect with scene referred linear footage. However Flame has the good taste of computing gamma correction as power function which makes it much friendlier with linear footage. Anyone confused? Welcome to the wonderful world of colour management.

We are in the process of examining how to clean things up, and have recently introduced viewer data types which “understand” linear footage. Compositing with linear footage in Flame should not be a technical issue. As you look at more creative image processing tools, the lines become a bit more blurry, because the end result can indeed vary quite a bit when feeding certain tools with different colour distributions. As we move forward, you can expect us to make things clearer and simpler for the user. Right now, Flame should allow you to use linear images, visualize them properly, and create comps that will look good. But it does require some knowledge from the user on how to do things.

A good example is keying with linear images. Most keying algorithms make the assumption that you are dealing with a perceptually uniform colourspace. It actually makes the process of keying easier. Of course, scene referred linear space is everything but perceptually uniform! In the context of Flame, it means that your linear “scene referred” KeyIn should be passed through a video gamma compensation to provide the easiest extraction or colour selection. Ideally this should all be transparent to the user. It is not the case just yet I’m afraid, and I wonder whether it is that clear in other applications?… I suspect it isn’t quite that clear. If anyone wants to comment on this, please do, we’re quite interested in this type of feedback.

thanks

Philippe Soeiro

[nigel]

I gotta say I am a little confused by his email. It starts of by saying …. ah yes linear its all good, we are happy ……but the then it sounds to me like he is saying that actually it is not linear at all. For example .18 should be .18 not encoded to produce a monitor vlaue of middle grey. Does he say flames keyers are set to recieve gamma encoded footage… wow thats bad ! Colour suppression in Gamma encoded…… also probably not ideal.

this is like what Autodesk did in Maya and Max where they gamma encoded all the colour pots and added a sRGB lookup to the renderview somehow failed to mention it in the manual and have made it nigh on impossible to work around…. well actually they have improved things in Max slightly.

If we look at Shake for example there was a little button at the bottom of the keyer that allowed you to nominate the incoming colourpsace of the footage that was going to be keyed and then adjust the algorithims accourdingly. Nuke is still the best tool for linear float I have seen. It GREATLY simplifies the whole process..

I am not going to bash flame as it does many things brilliantly however its colour management and the way it hides it from users has always been a very sore point for film people !

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