Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] Tutorials & Guides => Topic started by: dubcat on 2016-08-03, 20:06:08
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Looks like Corona will be getting VFB LUT support soon.
Most of the LUTs you find online are made for different Log cameras (Both free and paid ones).
These LUTs come with a baked "master" contrast curve.
When you apply these LUTs to your Corona images you will get sRGB curve + that specific Log curve, and you end up with a super over-contrasted image.
I've noticed that most people "fix" this by lowering the opacity/fill of the LUT, or by adding a curve adjustment layer before the LUT. But there is a more correct way to fix this problem.
By removing the master curve.
I will also show you how I white balance my LUTs to make them more subtle.
To follow along you will need "3D LUT Creator", if you take LUTs seriously this tool is essential.
The example picture is by "Lotta Agaton", hope she doesn't mind.
So here is the original picture.
(http://i.imgur.com/Syuas4z.jpg)
This is the picture with a LUT named Manchester from deLUTs.
(http://i.imgur.com/4WlYS0p.jpg)
(http://How to fix LOG LUTs)
So fire up "3D LUT Creator" and go into the "Mask" tab. Change "External 3DLUT" to "Output". Click "Load LUT" and find your LUT file.
(http://i.imgur.com/B6kt8jl.png)
Click "Edit", "External LUT" and "Extract curve from Ext. LUT".
(http://i.imgur.com/Had9LQG.png)
Go into the "Curves" tab.
Here you can see that "3D LUT Creator" has extracted the curve adjustments from the LUT. While doing so it created a new LUT with the HSL adjustments, and loaded that new LUT into the LUT slot.
Click "M->RGB" to extract the "Master" curve from the R G B curves.
(http://i.imgur.com/J1VxH9A.png)
Click here to disable the "Master" contrast curve
(http://i.imgur.com/zpCm1R1.png)
Here is the result.
(http://i.imgur.com/R78GyyY.jpg)
How to White Balance LUTs
So we have fixed the "master" curve. But what if you want to keep the general "feel" of the LUT, but don't want that blue/green tint?
We will be White Balancing in "3D LUT Creator" because the result is awesome.
Download the special HALD image at the bottom of this post.
Apply your LUT to the HALD image in Photoshop like this.
Save the image as .png
(http://i.imgur.com/S0UehEi.png)
Open the HALD image as a normal image in "3D LUT Creator".
In the "A/B" tab select the "Color Picker" next to "Temp." and click on the grey spot at the bottom of the HALD.
(http://i.imgur.com/FlY2fkR.png)
Send the LUT back to Photoshop
(http://i.imgur.com/Ia2j7gg.png)
Go to "Image" and "Canvas Size"
(http://i.imgur.com/2Hgxk0W.png)
Change the "Anchor" to this one and "Height" to "4096"
I've made an action to do this for you.
(http://i.imgur.com/XDHzMQ6.png)
Save the image as .png again.
In "3D LUT Creator" go to the "Mask" tab and click "Load LUT", select the .png you just saved.
(http://i.imgur.com/RzmKqxa.png)
Here is the result. White Balanced, now you can adjust the opacity to taste.
(http://i.imgur.com/UdyHeCr.jpg)
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You're probably gonna kill me, but I like the look of that first, uncorrected, contrasty LUT the most :D If it was me, I'd just tone the exposure down a little after applying that LUT, and I'd call it done :D
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I don't know what camera those deLUTs are made for, but the master curve ain't that bad. I was just being over dramatic for over dramatic sake.
Here is a LUT made for Cineon, this is a better example.
Original LUT - Canon EE
(http://i.imgur.com/OmuBafS.jpg)
Fixed LUT
(http://i.imgur.com/mAzDWn0.jpg)
If we get LUT as last chain before white balance in Corona, you can just crank up the contrast yourself.
This is just my opinion, but I think of LUTs as a mood. I want to scroll through my LUT library and find the right mood for the image.
Contrast is basically when R G and B is at the same position. When we remove the contrast (master curve) from a LUT, we get a "pure" impression of the LUT.
When the mood is set, we adjust the contrast to taste (If Corona can be nice and do this before the LUT, and change the Contrast to work in sRGB space). When the contrast is baked into a LUT, it's like telling someone to always render at 2EV with 1.65 Compressed Highlight. (Hmm, why did dubcat say 1.65 CH?, that's kinda specific and odd number)
Audio people can relate to this with dB. You can't really hear what an EQ or compressor does, if the output is louder then the input. When the output has the same LUF/RMS as the input, then you can hear what the EQ/Compressor does. If the dB is louder then the input, our brain automatically think it's better. There is a reason why we have "The Loudness War". Damn, my brain has begun to merge RGB and dB!
TLDR; Contrast/Louder dB = Taint (in dubcats opinion)
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Just to understand this whole LUT craze better: the main advantage is that you can quickly apply these presets, right?
Because I can imagine altering an image in PS to make something _similar_ to the final result in 5-10 minutes using levels and color balance.
Don't misunderstand me please, I just don't want to be an ignorant, I want to understand this. :D
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I use LUTs to emulate real "Camera Response Curves".
But if you are using crazy LUTs like Manchester, the only advantage is that you can flip through them and find something you want quickly.
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Just to understand this whole LUT craze better: the main advantage is that you can quickly apply these presets, right?
Because I can imagine altering an image in PS to make something _similar_ to the final result in 5-10 minutes using levels and color balance.
Don't misunderstand me please, I just don't want to be an ignorant, I want to understand this. :D
Partly, but I believe this is pretty good reason on its own. You can put a lot of color correction into single LUT file and share across frame buffers of applications that use different CC paramaters or none at all. So you will get the same look from Photoshop/Nuke/etc.. into Corona, Unreal Engine, etc.
You can get your result in 10 minutes, but I can already get that result from 1 minute I opened 3dsMax scene and did my test render.
And what Dubcat writes, it lets you emulate camera response so you adjust your framebuffer look like you would in camera. Instead of the arbitrary CGI look. Small difference that can matter big time.
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Got it! Thanks guys!
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Very nice write-up and bit of knowledge, many thanks for this.
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Hey Dubcat, I cant seem to see LUT support in Corona roadmap, do you know more precisely when LUT implementation is comming?
Thanks.
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I will let Team Corona answer this question. There was a thread asking about what LUT features we wanted.
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with some luck, we can make it in 1.5
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with some luck, we can make it in 1.5
That would be beautiful, thumbs up for it.
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Can you use 3D Lut Creator to "batch convert" multiple LUTS (.cube) files?
I would be very tedious to convert every file individually for those color grading LUT preset packages you can buy.
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All this stuff need multiple clicks. I guess the best solution right now would be to automate it with https://www.autoitscript.com/site/autoit/ and afk.
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I just wanted to say that I wrote an e-mail to 3DLUT Creator support to add a feature to change these LUT files with a BATCH. So if you have many LUT files you can convert them without having to convert each one separately. This is the reply I got:
Hello!
So, I added those functions.
Here's example command line parameters needed to do what you're after:
LutCreator.exe image.jpg /Action:LoadExtLut:"D:\Dropbox\Photoshop Presets\Presets\3DLUTsAll\Log\LOG_LC3DL_Fuji3510_log2hd_ConstLclip.cube" /Action:SetExtLutPosition:3 /Action:ExtLutExtractCurves /Action:CurvesExtractMaster /Action:SetMasterCurve:off /Action:ExportLut:m:\test.cube
Please wait for the next version to test it. =)
So it's coming in the new version of 3DLutCreator.
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When the contrast is baked into a LUT, it's like telling someone to always render at 2EV with 1.65 Compressed Highlight. (Hmm, why did dubcat say 1.65 CH?, that's kinda specific and odd number)
I would really like to understand the meaning of this obscure reference, highlight compression = 1.65. Why?