Help Needed understanding Gamma/LUT Correction

[danb4026]

Ok, I was at the DMVC in Boston and this topic came up in relation to the infamous linear workflow.

 

Bottom line for the most consistency set gamma/lut correction in max prefs to enabled and at 1.8. Set input and output gammas to 1.8 aswell.

 

The material editor will brighten up but thats fine. Now all materials that you are used to using will not really be good anymore. Whites will be brighter, etc. Although this is a pain...the eventual gain is that all scenes have more light and require less work to render and produce light.

 

Now the problem is getting it to look the good in PS. I could use some help here too...please

[Crazy Homeless Guy]

In photoshop, the images apear washed out, in other programs like photo viewing programs, they appear to have no gamma correction at all.

 

Wassup with that? Is it a PS setting?

 

What type of format are you saving as? If you are working in float, you either need to save as a floating point (EXR or HDRI,) or burn a gamma into the image equal to the gamma you are working with.

[danb4026]

I have always saved as a JPEG. What difference does it make what type of file it is and what do you mean by "float" and how do you "burn" a gamma into an image?

[Crazy Homeless Guy]

This is where my explanations and vocabulary are lacking.

 

Essentially, a gamma corrected image has the gamma 'burned' into it so that it so that it correctly displays on our monitors. Typically it has a gamma of 2.2 burned in for Windows machines, or a gamma of 1.8 burned in for OSX machines.

 

An HDR image typically does not have a gamma burned into it. It usually has a gamma of 1.0. When you open a HDR image in Photoshop, be it EXR or HDRI, Photoshop will display it as though it is gamma corrected. Meaning, it will appear as though it has a 2.2.

 

If you are working in true LWF, and saving to a 8 bit format, then you will need to save it with the gamma that you are planning on working with. If you do not save it with the gamma, then the image will appear overly dark in photoshop, and you will have to apply the correct gamma to it. This is bad.

 

If you work in true LWF, and are saving to a HDRI or EXR, then you want to make sure that you are saving it with a gamma of 1.0. If you save it with the gamma burned in, then you will have a overly bright image in photoshop, and you will have to apply a 'negative' gamma to correct it. This is also bad.

 

Basically, when you open your image in PhotoShop, it should look the same as it did when it saved from Max.

 

Now, I am not sure I used the term floating point correctly. I think floating point when it comes to images only means that the format is capable of containing color information beyond what our monitors will display. ..or maybe it is what we can see. I think PhotoShops HDR plug-ins (EXR, and HDRI,) are programmed to automatically display a certain gamma. I really need to research that part more.

 

I think I tried to hard to explain, and just made it sound confusing.

[SandmanNinja]

F10

Renderer tab

Frame Buffer Type

[Crazy Homeless Guy]

What is your gamma output set to in the Max preference dialog? ...also, are you using color workspace are you using in PhotoShop, and if your monitor is calibrated, what is it calibrated to?

[danb4026]

I enabled Gamma/LUT Correction & Load Enable State with Max file.

Gamma set to 1.8

Check "effect Color Selectors"

Check "Affect Material Editor"

 

Bitmaps input = 1.8

Bitmaps output = 1.8

 

The only thing not checked is "Autodesk View LUT"

 

I set my gamma output to 1.8 in max's prefs. Whe I open the file as an exr in PS, it is a bit washed out, but as a JPEG it looks fine, matches my rendrering great. I am using Working RGB in PS.

[Crazy Homeless Guy]

I enabled Gamma/LUT Correction & Load Enable State with Max file.

Gamma set to 1.8

Check "effect Color Selectors"

Check "Affect Material Editor"

 

Bitmaps input = 1.8

Bitmaps output = 1.8

 

The only thing not checked is "Autodesk View LUT"

 

I set my gamma output to 1.8 in max's prefs. Whe I open the file as an exr in PS, it is a bit washed out, but as a JPEG it looks fine, matches my rendrering great. I am using Working RGB in PS.

 

You have your output gamma set to 1.8, which is means that any rendered file you are saving has this gamma value saved with it. When saving to EXR formats, you typically save out the files with a gamma of 1.0. When you open your EXR file in PhotoShop, it will display it with the gamma of the color space you are working in. Hence you are applying a gamma correction of 1.8 when you save out of 3dsmax, and you are applying a gamma correction again when you open the file in PhotoShop.

 

Bassically you are double gamma correcting you EXR's. If you set 3dmax's output gamma to 1.0, and save a EXR, then your EXR should open fine in PhotoShop.

 

But you jpeg will appear to dark.

 

To illustrate this, open one of your EXR's that appear to bright in PhotoShop. Now use the exposure control to adjust the gamma to 0.555. It should now look identical to you rendering as it was in 3dsmax. The 0.555 is the inverse of one of the gamma's. It is basically removing one of the gamma's that you applied to the image.

 

The equation.....

 

1 divided by 1.8 equals 0.555

 

or

 

1/1.8 = 0.555

 

While this corrects your image, it should not be the way you work. If you are going to leave the output gamma in your Max pref settings to 1.8, then you need to be saving out as a TIF, TGA, Jpeg, or other standard format.

[SandmanNinja]

I'm gonna have to re-read this a few times.

 

I just rendered a scene with frame buffer set to 16-bit and saved it to a JPG and it's too dark in photoshop and web browsers.

 

I set the frame buffer to 32-bit, saved it as a HDR, opened it in photoshop - and it looks the same as in 3DS. I adjust the image to 8-bit, save it as a JPG with no gamma correction, and the final jpg looks fine.

 

Am I doing it right?

 

(edit: I need coffee)

[Mike.]

THAt is a revelation for me. i never cared about all this gamma thing.

Just spent 2 hours reading, and i must admit i've been doing things the wrong way for some years now!!

 

thanks all for sharing your knowaledge.

[SandmanNinja]

Oh - I'm starting to see the light.

Let me get this straight.

 

The gamma correction depends on the file format that I'm saving to?

 

So:

If I save to a JPG, TIF, BMP, any-8-bit-format, set OUTPUT GAMMA to 1.8

If I save to a HDR, EXR, or any 32-bit format, set OUTPUT GAMMA to 1.0

Hope I can wrap my head around this.

 

[time passes - experiments performed]

 

Okay - I think I finally get it.

 

I click Customise -> Preferences -> Gamme/Lut -> set gamma input and output both to 1.0

 

I click Render -> Renderer tab -> Frame Buffer set to 32-bit

 

I did a very basic render with a HDRI and a primitive.

 

If I set the OUTPUT GAMMA to 1.0 and save it as a HDR, then it looks just like it does in 3DS.

JUST CHANGING THE FILETYPE TO JPG yields a very dark image - wrong gamma.

 

If I set the OUTPUT GAMMA to 1.8 and save it as a JPG, then it looks just like it does in 3DS.

 

So, I need to adjust my OUTPUT GAMMA according to what my file type is going to be.

[AJLynn]

Yes, you've got it. And I still say Max's gamma handling is really messed up.

[shaneis]

Yes, you've got it. And I still say Max's gamma handling is really messed up.

 

Completely agree. Maya's just as bad. Much better to render to a 32-bit format and apply gamma correction and tone-mapping in post.

 

On a side-note, have been experimenting with Cinepaint for the last week. Excellent with exr! Currently linux-only, but the developers are working on a Windows port. Stay-tuned or install linux...choice is yours

[Crazy Homeless Guy]

Now I need to do some experimenting to see if I should be working with a gamma of 1.8 instead of 2.2. I have been using 2.2 for the last couple of years, but most in this thread like a 1.8, and Rodrigo Neoscape was pushing 1.8 at the DMVC.

[Tim Saunders]

Ninja, Thanks a load for the summary of your understanding of Travis's explanation. It simply wasn't clicking for me, He's just smarter than me, or his hair is just cooler than mine (it is by the way).

 

I still have problems with hdr and exr renders, even set at 1.0. 1- they appear too dark in the frame buffer, 2- they still open with the washed out look of 2.2 in photoshop.

 

At least 8 and 16 bit images are opening great in photoshop--and for that, I am ready and able to have babies for both Ninja and Travis. I'm sure I'll see you in SanFran next year if that's where they decide to hold DMVC09.

 

Anyway, I suggest rendering tifs (either 8 or 16-bit) as you can open them as Camera RAW images for extra control.

[Crazy Homeless Guy]

Ninja, Thanks a load for the summary of your understanding of Travis's explanation. It simply wasn't clicking for me, He's just smarter than me, or his hair is just cooler than mine (it is by the way).

 

I still have problems with hdr and exr renders, even set at 1.0. 1- they appear too dark in the frame buffer, 2- they still open with the washed out look of 2.2 in photoshop.

 

At least 8 and 16 bit images are opening great in photoshop--and for that, I am ready and able to have babies for both Ninja and Travis. I'm sure I'll see you in SanFran next year if that's where they decide to hold DMVC09.

 

Anyway, I suggest rendering tifs (either 8 or 16-bit) as you can open them as Camera RAW images for extra control.

 

That is the funniest thing I have read in awhile. Was your wife aware of your ability to conceive before she was pregnant? If not, you might want to keep that to yourself.

 

I think I will switch to 16bit tiff for awhile, and see how it works. If nothing else, it should save a lot of server space.

[SandmanNinja]

Ninja, Thanks a load for the summary of your understanding of Travis's explanation. It simply wasn't clicking for me, He's just smarter than me, or his hair is just cooler than mine (it is by the way).

 

I still have problems with hdr and exr renders, even set at 1.0. 1- they appear too dark in the frame buffer, 2- they still open with the washed out look of 2.2 in photoshop.

 

At least 8 and 16 bit images are opening great in photoshop--and for that, I am ready and able to have babies for both Ninja and Travis. I'm sure I'll see you in SanFran next year if that's where they decide to hold DMVC09.

 

Anyway, I suggest rendering tifs (either 8 or 16-bit) as you can open them as Camera RAW images for extra control.

 

HAHAHAAHHAH....

 

Awesome...

 

Wish I could pull chicks that easy...

 

Glad I could help - think your post is the highlight of my time here.

[RyanSpaulding]

So to recap the settings, whats below in the image is correct?

[AJLynn]

Depending on your workflow you may also need input gamma at 1.8, and then affect color selectors can be useful.

[RyanSpaulding]

Ah, ok. If I dont want to mess with the bitmaps gamma or anything like that, and instead just the scene I should leave the input gamma alone, correct?

 

I still dont understand the advantage of using input gamma as you'd then have to correct all your bitmaps to reflect that, right?

[AJLynn]

Most bitmaps will be gamma'ed to look right on a monitor, e.g. at 1.8 or 2.2. Max expects them to be at 1.0, so the bitmaps will be read incorrectly and Max will interpret them as being brighter in the midtones than they ought to be. This causes a lot of washed out looks and lighting that ends up overbright because surfaces are giving off more GI than they should. Input gamma of 1.8 or 2.2 fixes that by changing Max's expectation of what the gamma of the incoming images is. Output gamma of 1.8 or 2.2 is to fix the problem of Max outputting images that have their gamma too low for the monitor.

 

The alternative woud be to first gamma the bitmaps down in Photoshop, and also correct your color swatches, then gamma the output images back up. Changing it in Max instead keeps gamma consistent, e.g. makes it linear, which is what the Linear Workflow thing is about.

[RyanSpaulding]

Ah, now I get it! Thanks a ton for that. Would any settings in the VRay Color Mapping need to be changed then? I have all set to default.

Edited May 19, 2008 by RyanSpaulding

[RyanSpaulding]

Here's an updated settings image.

[AJLynn]

Yeah, that's exactly how I've got it set up (and it's given me the best results that way) - only I'm using mental ray, but it should work the same way. Have you tried a test scene with it?

[RyanSpaulding]

Now yet, but I will when I get off of work today. All my ready-made scenes are at home...and at my new place of employment, I've only done a render of a highway...soooo, I'm going to have to wait.

 

I'll try rendering each option out.