Author Topic: Time to ditch sRGB/Linear as default (?)  (Read 34168 times)

2018-10-26, 17:18:32
Reply #135

kosso_olli

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...we dont even know why some tone mappers look more realistic than others.

A user here on the forums (dubcat I believe) posted a way to analyze two images. The result was a curve that represents the difference between the two. So if you have a raw linear render from fStorm for example, and another tonemapped one, you could try to analyze what is going on there by looking at the output curve. Just an idea, maybe ask dubcat... I am highly interested in this as well, because I feel the 32bit linear workflow is not suited for the needs of most users here.

There is no need to analyze anything here we know what happen on the Fstorm side. It's using the ACES output transform instead of the sRGB one. Tonemapping controls can be whatever you want before applying the output transform (which must be the final step), it's just a matter of taste.

Um, I am not quite sure if it really is that simple. On which sources are you relying to make that statement?
The V-Ray guy checking out Corona...

https://www.behance.net/Oliver_Kossatz

2018-10-29, 14:08:15
Reply #136

IsmaeL

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OK, this thread explains why there is a new feature in the poll called "rework tone mapping"

I totally agree with Ondra on reworking the usability. I would start by taking a good look at Camera RAW and how it works. The fact that you can change values with the arrow keys is very convenient. I also like the curves they have implemented in CR. The curves we have now in Corona have to many options and you can't do anything very precisely.

Even white balance should work like in PS, with a blue-yellow slider and a green-magenta one. This was already pointed out by Juraj.
 
That being said, the color wheels some programs use are awesome. Specially for some color grading.

On top of that I would really like to see a Histogram and maybe even a Spectrogram and other useful tools for video.

This might seam a little overboard but I feel that doing POST in Corona should be the goal. I don't want to open up a separate piece of software just to do 3 things because I can't do them in Corona.

This would give people a very fast way to send WIP to clients and since we have Corona's CIE, you can always open the render and change any configuration.

But of course, for this to work the tools provided have to be as good as the ones you get from your usual POST software.
This means that Corona has to become aware of color space or at least give you the option to load you monitor color correction.

That brings me to the Filmic Highlight and Shadows. Just like Juraj said, they shouldn't be in Corona if they don't work properly.

As far as usability goes I would definitely appreciate a change on the whole VFB. Some buttons should be implemented or seperated.
Finally the history should NOT delete and work just like the one in Vray, where you can load your POST configuration.

Whatever the devs do I hope some of this is taken into consideration.
Falling in love with Corona

2018-10-29, 14:13:47
Reply #137

Juraj Talcik

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We do have histogram :- ) just click on 'curves'.
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2018-10-30, 09:56:09
Reply #138

IsmaeL

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We do have histogram :- ) just click on 'curves'.

jajjaja that's true, forgot about that.
Falling in love with Corona

2018-10-31, 14:49:52
Reply #139

Fluss

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A thing I just read that I find very interesting and also raises a few questions about ACES and RGB in general:

http://nbviewer.jupyter.org/gist/sagland/3c791e79353673fd24fa

https://www.colour-science.org/posts/about-rendering-engines-colourspaces-agnosticism/

I guess spectral rendering is the future otherwise we will always rely on cheats/artistry ;)

Really nice article, thanks for sharing, I missed that one! Conclusion: there is no perfect colorspace for rendering.

You are right, spectral rendering is the way to go if you want pure realism but it introduces some flaws too. Spectral rendering is quite slower and it's hard to convert standard RGB triplet to spectra as you have to deal with metamerism. I've read some recent papers that are introducing some nice solutions to improve those aspects btw :

https://www.ci.i.u-tokyo.ac.jp/~hachisuka/rgb2spec.pdf
https://graphics.tudelft.nl/Publications-new/2018/PBE18/PBE18.pdf (It looks like Ondra provided the pool scene for that one 😊 )

Anyway, if we have to use RGB triplets, the colorspace that provides the most (AVERAGE) accurate results (compared to ground truth spectral render) is the ACEScg one, see this :

https://www.colour-science.org/anders-langlands/

And this around 18 min.


That said, the Academy Color Encoding System introduces a whole bunch of stuff. What was discussed in the first place was the tonemapper itself. Using ACES for rendering is not mandatory. We can still use the tonemapper converting linear sRGB to display output and then, benefit from the nice Filmic Curve it provides. It will still remain miles ahead of what we have now imho.

The tool they use in the video to explain the tonemapper controls can be accessed here: https://www.desmos.com/calculator/h8rbdpawxj

@Devs you really should look at the UE4 post controls (around 45min in the video), that would be a good starting point for the tonemapping and grading tools rework.

« Last Edit: 2018-10-31, 15:03:08 by Fluss »

2018-10-31, 18:02:15
Reply #140

IsmaeL

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This was very interesting. So we basically have all we need in Corona but the UI is a bit all over the place.

We can already do this with the curves or use a LUT from Adan Martin which emulate the behaviour of different photo stock.

The only thing different in UE4 is that they use a specific curve with base values, in this case ACES.

So to sum up, we get rid of the Filmic highlight and shadows and replace it with a new section called tonemapping or filmstock.
Of course you can deactivate it like all the sections in the Corona VFB. ;)

That is pretty much what you guys are asking for
Falling in love with Corona

2018-11-07, 11:54:36
Reply #141

Rhodesy

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Im new to corona for Max but I've been a long time C4D corona user. C4D natively saves PSD files and if you chose the 16bit option the file with all the pass layers in it is linear. This gives a nice subtle addition for painting in extra reflection etc. Ive noticed with having to save as 16 bit tiff files in Max the files are srgb and you lose that subtlety, having to turn the layer transparency right down and having highlights blown out. Is there something Im doing wrong? Can I get 16 bit linear out of MAX?

2018-11-07, 12:34:05
Reply #142

romullus

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Yes you can, in save as dialog, choose override gamma and set it to 1.0
I'm not Corona Team member. Everything i say, is my personal opinion only.

2018-11-07, 13:34:47
Reply #143

Juraj Talcik

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Yes you can, in save as dialog, choose override gamma and set it to 1.0


I believe this still gives you output-referred integer Tiff, not linear half-float file. It will just contain the data correctly, but with no leeway as it will clamp.

And that is outside of some weird idiosynchracies 3dsMax has with Tiff file in general.  If you want linear half-float file for compositing, just choose .exr in half-float, it will have all the data and will be substantially smaller in size.

Rhodesy, there is also .PSD plugin that saves all passes for 3dsMax if you want to avoid saving to .exrs and having ProExr in Photoshop.
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2018-11-07, 14:04:56
Reply #144

romullus

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Hmm, it would probably make clamped image, but yet without gamma curve baked in. How we should name such output then, half-breed linear perhaps? :]
I'm not Corona Team member. Everything i say, is my personal opinion only.

2018-11-07, 14:58:58
Reply #145

Juraj Talcik

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The gamma curve would actually be there, only the values would be converted :- ). Highlights would be compressed to smaller range.

So while adding the passes up, it would make the original image fine, some operations would probably miss the precision they would have from actual scene referred format.
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2018-11-07, 15:46:59
Reply #146

Rhodesy

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Thanks Romullus and Juraj.

Is that the Cebas PSD manager you refer to Juraj? Im trying to reduce extra subscriptions where I can now we have Max. Does it do anything other than write multipass PSD files? The half float exr might be an option. The 32bit version is a non starter for me with the file sizes and the mine field of 32bit so a 16bit variant might work best. Is that what you use? The exr plugin works well I seem to remember when I tried it last.

Cheers

2018-11-07, 16:35:45
Reply #147

Juraj Talcik

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What do you mean 'minefield of 32bit' ? Mind you, 16bit .exr acts defacto as 32bit file, only with half as data. 16bit .exr has nothing in common with integer 16bit files like Tiff, PNG,.. 

To composite render passes together with correct math you need to be in linear space, which always happens to be in 32bit mode per channel anyway. The Cebas PSD manager would create 32bit PSD file as well, Photoshop can work in linear only in this mode.
 I think you know all this, but just to make sure I am not understanding something wrong from you :- ).


I use 16bit tiff, but I don't do any compositing nor do I have access to dynamic range anymore. Advantage of 16bit Tiff as opposed to 8bit is only in better tonal gradation, so wider range of tones to avoid posterization effect or other artifacts. Nothing else, no highlight or shadow recovery. All those I do previously in Corona framebuffer.
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2018-11-07, 17:08:47
Reply #148

Jpjapers

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What do you mean 'minefield of 32bit' ? Mind you, 16bit .exr acts defacto as 32bit file, only with half as data. 16bit .exr has nothing in common with integer 16bit files like Tiff, PNG,.. 

To composite render passes together with correct math you need to be in linear space, which always happens to be in 32bit mode per channel anyway. The Cebas PSD manager would create 32bit PSD file as well, Photoshop can work in linear only in this mode.
 I think you know all this, but just to make sure I am not understanding something wrong from you :- ).


I use 16bit tiff, but I don't do any compositing nor do I have access to dynamic range anymore. Advantage of 16bit Tiff as opposed to 8bit is only in better tonal gradation, so wider range of tones to avoid posterization effect or other artifacts. Nothing else, no highlight or shadow recovery. All those I do previously in Corona framebuffer.

Thats very interesting! So essentially unless you have a 32bit exr you lose the ability to accurately step down exposure etc?

2018-11-08, 00:19:01
Reply #149

Juraj Talcik

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No, it can be many other scene-referred file formats, like various camera raw formats which are often 12bit at best. But for CGI there are fewer: 32bit full-float .exr/.hdr/.tiff and half-float 16bit .exr/.tiff . I do not believe 3dsMax supports 16bit half-float Tiff, this is very obscure format, I think only used internally for Adobe's DNG or something along that line.

16bit integer Tiff with embedded gamma curve (regardless of in which gamma you write those colors in) is not the same thing as linear 16 bit half-float .exr.


Then it matters how you extract the information from that format. If you open 16bit .exr in Photoshop, it will open it in linear 32bit environment and will be able to extract shadows/highlights /manipulate exposure or tonemap. The file itself (16 bit .exr) will have obviously less information than 32bit file but you rarely need this for post-production (while you do need it for image based lighting with above 16+ dynamic range stops, i.e. Sunlight for example).

If you change the environment to 16bit in Photoshop, it will instantly clamp (or tonemap, it gives you options) and you won't be able to extract any further dynamic range. 16bit will still give you the advantage of wider tonal gradient to avoid artifacts and posterization effect. 16bit Tiff/PNG/etc.. will open to this mode directly unlike .exr. But even if you open them into 32bit environment, they will still be clamped.


TL:DR :- )

16bit Tiff from 3dsMax if you already used highlight compression in Corona and only want to adjust local contrast, colors, etc. Edit in 16bit PS mode. (Save as 8bit for web/print at the end).
16bit .exr if you want to composite or extract dynamic range operations (exposure, highlights, shadows, tonemaping, glare/bloom, etc..). Edit in 32bit PS mode.
« Last Edit: 2018-11-08, 00:32:12 by Juraj Talcik »
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