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Gamma Converting

25 REPLIES 25
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Message 1 of 26
FalconCrest
200 Views, 0 Replies

Gamma Converting

How do I render the composition with Gamma 2.2 ? How can I convert any images that are Gamma 2.2 (sRGB) to linear Gamma ? I use EXR images which are linear gamma, so no worries as far as I know 🙂
25 REPLIES 25
Message 2 of 26
morazz
in reply to: FalconCrest

when you bring your footage in, there is a options tab. You can convert it there, on import.
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 3 of 26
PiXeL_MoNKeY
in reply to: FalconCrest

Use an sRGB Node before the output node. It appears that the output file format controls for Gamma don't work. NOTE: you should output to an 8bit format with the output node set to 8bit.

-Eric
Message 4 of 26
morazz
in reply to: FalconCrest

Sorry man, I thought you where talking about import, but as Eric has said the output option is a bug, and effects all file formats. This should be fixed
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 5 of 26
FalconCrest
in reply to: FalconCrest

I placed my sRGB node before the output and it's set to 8 bit. Then following Mark R to view Gamma non-linear gamma in composite viewer and setting the exposure to 2.2 the composition does not look right at all. Then again that is only to view the composition at non-linear gamma in the player. What about rendering ?
Message 6 of 26
PiXeL_MoNKeY
in reply to: FalconCrest

The sRGB node converts it to gamma 2.2, so you don't need the player modification as it is already showing gamma 2.2. So what you see in the output (without enabling the gamma in the player) is what it will render.

What you posted is causing double gamma conversion sRGB (gamma 2.2)+player (gamma 2.2).

-Eric
Message 7 of 26
morazz
in reply to: FalconCrest

What Eric says is correct, on the output node or if you hit 7 for output view, you will get the double gamma, however, if you should be using node view or 6, then having your vLUT as you have done, will work fine, you just have to remember that the vLUT is not effecting the output, only the sRGB tool is. What I would suggest for a workflow is mute the sRGB until you do your final output, when you render turn it on and you will have the best of both worlds.

cheers
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 8 of 26
FalconCrest
in reply to: FalconCrest

The sRGB node is before the output. When I remove the sRGB node, the output preview looks fine. When I place the sRGB node before the output things don't look right in the preview viewport. Eric mentioned that is because there is double gamma happening.

Since sRGB is converting any images in my composition to linear gamma (I hope it's excluding EXR files which are linear to begin with?), how do I setup the player view to Gamma 2.2 ?

The overall goal is to keep non-linear images (EXR etc) linear, strip Gamma 2.2 or sRGB images of their non-linear gamma then rendering and previewing the composition as Gamma 2.2 so far from the replies I haven't quite understood or it's not working.
Message 9 of 26
morazz
in reply to: FalconCrest

Here are the steps,
1. Load exr footage, it is linear light
1a. Load srgb/gamma 2.2 material, in the image loader you can remove 2.2/srgb so you now have a linear light image.
2. Do your work as you normally do.
3. Prior to the output node put a srgb/gamma 2.2 node to add back gamma curve
4. Render out.

Note1. The output option for gamma curve options is not working.
Note 2. When working, make sure the gamma 2.2/srgb node is muted or off so it does not display a double gamma in the viewport. The output will always be correct but the viewport will not show you the correct result if you leave it on. When muted the srgb vlut that you apply in the passthrough for the viewport will show it as a srgb gamma, but you are actually working in linear light.

Correct me if I am wrong but did I not do a tip on this topic

Cheers
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 10 of 26
FalconCrest
in reply to: morazz

1a. Load srgb/gamma 2.2 material, in the image loader you can remove 2.2/srgb so you now have a linear light image.


MarkR - When you say the image loader do you mean the image import tab ?

When muted the srgb vlut that you apply in the passthrough for the viewport will show it as a srgb gamma, but you are actually working in linear light.

I don't understand what you mean ?....
Message 11 of 26
morazz
in reply to: morazz

Ok sorry for all the bad writting, I was doing on my phone in bed late last night... could not sleep. 🙂

Anyway, let me try again:

If you have scene linear material also known as linear light material, and your final output you want to apply a gamma 2.2 or sRGB so it looks correct when viewed in the computer. Follow these steps:
1. load the material with a image import node.
2. since there is nothing to remove gamma wise, no need to add anything.
3. put a sRGB node (if that is what you want) prior to the output node.
4. Do all your work
5. Then render as normal then the material will come out with gamma 2.2 applied.

The issue I am trying to address is when you want to work with nodes and you are not viewing the output node in the player view, you will see your material in scene linear mode, to see it with the sRGB you need to apply a vLUT or ViewLUT to the display passthrough. This will, and you watched my video, so you know what is going on, apply the sRGB gamma curve to the image without actually effecting the image. It is just a way to view your material with a LUT. The problem comes when you want to view the output nodes which is after the sRGB node which is effecting your material. You then see a double gamma. If you mute the sRGB while you are working then everything will look fine and be correct, when you are ready to output your composition, just turn on the sRGB node again and it will render out your material with the correct gamma and all is good!

Now if you have material being loaded into your composition that had a gamma already on it, like a digital photograph, you can go to the options tab on the image import node and you can set it there to remove the gamma. It then converts the material to scene linear and then you just follow the rest of the above and it will work as expected.

Hope that helps.

cheers
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 12 of 26
hemmerli
in reply to: FalconCrest

i want to point out that number 3 in marks listing, above, is a workaround, because the intended workflow (setting gamma in the output tab) is currently broken. this fact was stated by mark, as well as, eric, i just wants to emphizise it.

cheers!
rayk
Message 13 of 26
FalconCrest
in reply to: FalconCrest

Now if you have material being loaded into your composition that had a gamma already on it, like a digital photograph, you can go to the options tab on the image import node and you can set it there to remove the gamma. It then converts the material to scene linear and then you just follow the rest of the above and it will work as expected.


What part of the options tab for image import ?
Message 14 of 26
morazz
in reply to: FalconCrest

How do you mean "what part of the options tab".

If you take in, for example, a jpeg image, it normally has a gamma baked in, normally a gamma of 2.2, when you use the import image node, you have a tab that is labled "Options". It is next to the Image Import tab. Under the Options tab you will see a title called gamma and RGB values that are grayed out because it is defaulted to none. If you select that blue flyout button, you will have options for Gamma, Rec. 709(HD monitors), sRGB. In our example I would select gamma, and set the RGB values to 2.2, which it defaults to. You have now set a gamma removal process on import. So when you put a tool after the image import node you are now working with scene linear.

I hope that helps. I do not know how else to explain it 🙂

cheers
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 15 of 26
FalconCrest
in reply to: FalconCrest

If you take in, for example, a jpeg image, it normally has a gamma baked in, normally a gamma of 2.2, when you use the import image node, you have a tab that is labled “Options”. It is next to the Image Import tab. Under the Options tab you will see a title called gamma and RGB values that are grayed out because it is defaulted to none. If you select that blue flyout button, you will have options for Gamma, Rec. 709(HD monitors), sRGB. In our example I would select gamma, and set the RGB values to 2.2, which it defaults to. You have now set a gamma removal process on import. So when you put a tool after the image import node you are now working with scene linear.

I hope that helps. I do not know how else to explain it 🙂

I apply Gamma 2.2 to the image, not Rec.709. Then with the sRGB node before the output node I set that to Gamma 2.2 as well that is double gamma. Or do I set the sRGB node before the output to 1.0 for all three values ?
Message 16 of 26
morazz
in reply to: FalconCrest

No this is not a double gamma, on loading material which I explain prior, you are removing the gamma first, then you have linear, then the sRGB node prior to output puts the gamma back into the image. I am leaving out the Vlut for now so I do not confuse you.

Does that make sense?
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 17 of 26
morazz
in reply to: FalconCrest

I thought I would do a video to better explain myself.

Please click link below to see my video. It is in a .mp4 format

Video link
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 18 of 26
FalconCrest
in reply to: FalconCrest

My question was almost answered and I appreciate the video it was helpful. I have a blend&comp node before the sRGB node and I notice a gamma difference between the blend&comp node and the sRGB node, is there something going on I'm not aware of ? When I do a test render it doesn't output right.
Message 19 of 26
morazz
in reply to: FalconCrest

Don't know, You need to send me the composition so I can look at it.
Mark Rasmussen
VFX - Supervisor | Compositor
Enigma|FX

TOXIK/Composite BLOG
http://enigmafx.ca/efxblog
Message 20 of 26
jonavark
in reply to: morazz

Thank you Mark. !

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