Gamma and Backburner

[Mark Cronin]

I don't like to post multiply threads, but I thought that this issue was something to do with mr's photographic exposure control ,but after more testing I have discovered that its purely a gamma thing!

After quite a bit of research I enabled gamma correction under preferences, and set the gamma level, input, and output all to 2.2. Both affect colours and affect materials are checked. With a bit of tweaking and using the new mr photographic exposure control, I managed some good results.

But my problems started when trying to send an animation through backburner. The frames on my pc came out right, but all the frames from the nodes came back overly bright and washed out. For test purposes I saved the files as jpegs with gamma overide of 2.2 to a central server. The material maps are all on a central server too.

Update:I've tried saving the files with no gamma overide and different file types like floating point tif with gamma of 1.0 & 2.2. Still no luck! Has anyone come accross this before?

I tried changing the gamma preference settings on one node to match my pc and rendered a few more frames, but the problem is persisting - no change at all in brightness etc.

Now this is where I get really confused?!

With the gamma preferences set on my pc there doesn't appear to be any difference at all between an image saved with system gamma or saved overidden at 2.2 (on my pc). So I am unsure as to what the correct setting should be?

I tried both settings on the nodes and they don't make any difference there either (well they at least look the same in windows image preview). If I disable gamma correction on my pc the render nodes return images the same as my machine (both washed out). Ideally I would really like to use gamma correction because I could get much better results with regard to correct material results. I must be missing something that will enable it to work correctly with backburner?

Is there a setting somewhere that I haven't checked?

Any help would be appriecated......

Cheers, Mark.

[Brian Kitts]

have you tried playing with the "load enable state with max files" option under the gamma preferences, to see if that has any effect?

I always leave the max gamma output set to 1.0 if I'm saving to a jpg I will tell it to use a gamma of 2.2 in the render engine, or I will save it to an EXR and photoshop will know the make the adjustment.

setting the max output to 2.2 will double your correction as was mentioned in your other post.

[Mark Cronin]

Hi Brian,

Thanks for your post. Yeah I did try checking and unchecking load enable state option on both my pc and one node, but it didn't affect the images. I must admit that I don't really know what its meant to do?

The thing that really confuses me is that I can't see a difference between an image saved with system gamma or with the 2.2 override set. I understand that it should double the effect, but when I look at it in the windows picture and fax viewer there is no difference between them? Maybe this could be a setting in windows that is throwing it all out? Either that or for some reason backburner isn't sending the gamma override instructions to the nodes.

Guess I'll just keep looking for more info.....

[Brian Kitts]

Yeah I did try checking and unchecking load enable state option on both my pc and one node, but it didn't affect the images. I must admit that I don't really know what its meant to do?

It stores the gamma preferences for a scene with the file. For instance if I open an old scene before I started using LWF I would need to go into the prefs and turn off the gamma correction since I didn't use it back then when the scene was setup. If I had turned that option on in the past it would know to turn the gamma correction off for me.

Then when I go back to a recent scene that was created with LWF it would recognize that I have my gamma prefs off, knowing that scene requires them on, and it would ask if I want to change the gamma prefs based on whats embedded in the file.


As for your gamma thing.. I never use the override feature in the file save options. If I had to guess that's why you keep getting the same result, because no matter what you set before you render, the file you save is dictating all of your gamma.

This should be way easier than you are making it on yourself.

Leave your max gamma & LUT settings as you mentioned before, don't use the override (ever).

rendering to JPG set the output gamma in max prefs to 2.2 (leave gamma in file save options to use system default)

rendering to floating point image (EXR or TIFF) set the output gamma in max to 1.0... image will appear dark in max buffer and look correct when opened in photoshop....... this is where the vray frame buffer comes in handy to correct the on screen buffer when your gamma is set to one, I don't know if MR has an equivilant to make the adjustment on the viewport but not the saved data.

although now that I think about it, if MR doesn't have a correction capability in the buffer, when rendering to a floating point image, you could set the max prefs output gamma to 2.2 so that it looks good on the screen, then when you save the file out, use the override (I know I said never use it), and override the file's gamma to 1.0


is your brain on fire yet?

[Mark Cronin]

Totally fried!

I'll double check all the gamma settings and start testing it again when I make back to the office tomorrow.

Thats for you help!

I'll post back when I get it sorted (hopefully)!

Cheers

[Mark Cronin]

Well I've now got a much better understanding of all the settings, but I'm still having issues! I've attached my settings used and the results. I'm getting accurate results from my pc but blown out ones from the node via backburner. I can get accurate results from the nodes by changing the output (under preferences) to 1.0, but them my pc returns dark images. I cannot achieve the same light level from both my pc and a node using backburner with gamma correction enabled. I really think that this is an issue with BB now! It doesn't appear to be sending the correct gamma info to the nodes. Does anyone have any similar experiences?

I know that I could just turn off gamma correction or not render from my pc, but I shouldn't have to! Any suggestions?

[Brian Kitts]

just getting back to this thread after being out of town for a week.....

Based on what you've said so far, I would leave max's gamma set to 2.2 so that it always looks correct on your screen locally.

If backburner is returning images that are overbright with that setting, then just remember anytime you send a job to the network to use the override control in the save file settings. Since its coming back too bright that means your gamma is getting doubled, so you need to apply an inverse curve of the 2.2 value to compensate.... which is a value of "0.45" , so you should get a proper looking image back from the network with that correction.

[Mark Cronin]

Hi Brian,

Thanks for your reply. As you've mentioned, I've settled with the fact that the images from the nodes have to be over-ridden or corrected. Up until now I've over-ridden the save to 1.0, but I'll try the 0.45 correction factor too. Its not the end of the earth, just a hassle, but the results are worth it.

Cheers,

Mark

[Brian Kitts]

out of curiousity.... what file format are you saving to? did you figure out how you need one correction if saving to jpeg and another if going to tiff or exr?

[Mark Cronin]

Yeah, I've found that anything with floating point lighting info has to be saved to 1.0 and other file types such as jpgs etc saved as 2.2. I'm using rpf's at the moment for editing in combustion, saved with 16 bit colour, velocity and z-depth, etc.

Backburner still seems to apply double gamma correction, no matter what settings I use. I'm sure I'll find the cause of the problem one day, but for now I'll keep going as it is. I didn't have this problem before I enabled gamma correction, but the results with it on are much better, so its worth it.

Could be a backburner issue, but I'm sure more prople would have this issue if it were, guess its just a setting somewhere that I'm over looking. I'd take it up with autodesk but our subscription is part of the much larger company's group contract and they didn't want to pay extra for max support as there are so few seats of it. One day I'll sort it....