Author Topic: Beta 4 - Preview unlike render.  (Read 1010 times)

Offline Mr_Lamppost

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Beta 4 - Preview unlike render.
« on: July 03, 2016, 12:59:55 AM »
I know the preview is just that, a preview, and we expect there to be differences in the final render but while I am waiting for a final render I installed the beta on a second machine so I could try something else. 

This is just the default scene with an Easy Cloud (Not sure how useful they will be I usually spend some time tuning the cloud fractal(, layer added, I upped the coverage and density then lowered the sun, I was hoping the new cloud lighting would do a better job with this type of scene.  The preview looked promising although not quite what I was after.  The RTP looked similar to the regular preview so I did a default render and the result is totally different?

Comments...
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Offline bobbystahr

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Re: Beta 4 - Preview unlike render.
« Reply #1 on: July 03, 2016, 03:39:38 AM »
I know the preview is just that, a preview, and we expect there to be differences in the final render but while I am waiting for a final render I installed the beta on a second machine so I could try something else. 

This is just the default scene with an Easy Cloud (Not sure how useful they will be I usually spend some time tuning the cloud fractal(, layer added, I upped the coverage and density then lowered the sun, I was hoping the new cloud lighting would do a better job with this type of scene.  The preview looked promising although not quite what I was after.  The RTP looked similar to the regular preview so I did a default render and the result is totally different?

Comments...

Well only 1 iteration is showing as done out of 20 in the preview so that may make a difference. I wind up waiting quite a while for all 20 sometimes but allwys get an at least 90% accurate preview.
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Offline Matt

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Re: Beta 4 - Preview unlike render.
« Reply #2 on: July 03, 2016, 11:46:21 AM »
The RTP uses an approximation in the clouds that is less accurate than the final render. Sometimes it happens to look closer to what you want than the final render. That's accidental, but I suppose that will happen quite often when we do most tweaks while using the RTP. It's not ideal so I'm going to try to improve this in future.

Without this approximation the RTP becomes too slow to use (unless the number of voxels is much less than 1 million), because it spends so much time calculating the voxel cache before it even completes the first low-res pass, let alone refining to a reasonable resolution. For future versions I have an idea to make the RTP more closely match the final renders, it will just take longer to refine the RTP image. It would still use the approximation for the first few passes/iterations so that quick feedback is possible, and then render the higher iterations with the slow-but-accurate method. (In fact it won't just be one system or the other, it will progressively refine from the approximation to the accurate solution).

Matt
Just because milk is white doesn't mean that clouds are made of milk.

Offline Mr_Lamppost

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Re: Beta 4 - Preview unlike render.
« Reply #3 on: July 03, 2016, 01:49:24 PM »
Thanks Matt, that's more or less what I expected, I am used to seeing the lighting become more accurate as the preview refines.  It may just be this scene but both the regular and RTP previews had converged very quickly to their final state with very little change  from the first iteration.   I had let both processes complete, the RTP had restarted because I'd resized the window just before taking the screen grab. Doh.



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Offline ASK51

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Re: Beta 4 - Preview unlike render.
« Reply #4 on: July 20, 2016, 08:50:42 AM »
Hey,

I am also having issues with this, depending on the lighting of the scene its more or less obvious. I can totally understand what Matt means with the approximation of the clouds, but I dont really understand why this influences colors in the atmosphere as well.
Also, I am in general not sure why an approximation for accuracy on rendered clouds would introduce color shifts like that. From what I can see on your images Mr_Lamppost, its the same color shifts you have as I do. So everything thats blue-ish in the final render just looks a lot more orange in the preview.

We did some comparisons and corrections in Nuke with both images and there is definitely something going on with the colors. Also, I colorpicked the clouds at the same spot in preview and render (after applying an average blur to the same areas)

Preview value: 232, 230, 225 - Final Render value: 213, 215, 219. This is only a small difference at that point where I measured, but it spreads over the whole image and makes quite a significant difference in the whole images impression.

Here are some comparison shots:
From Terragen
65818-0

Comparison comped in Nuke, left is final render, right is preview
65820-1

So yeah, I really only care about color consistency and not image quality for preview vs. render. We want to make skies for HDR realtime rendering and would anticipate accurate results to have less guess work and trial and error involved.

Hope this gives some more insights :)

Thanks a lot!

Offline Matt

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Re: Beta 4 - Preview unlike render.
« Reply #5 on: July 20, 2016, 09:11:54 AM »
Thanks for posting those examples. I think it's probably due to the different GI engines used for atmosphere by the RTP and final renders. I could address this by having an option to render final atmospheres with the same GI engine as the RTP, or making the RTP converge towards the same GI as the final renders. I'll try to do one or both of these things for 4.0 or 4.1.

Matt
Just because milk is white doesn't mean that clouds are made of milk.

Offline ASK51

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Re: Beta 4 - Preview unlike render.
« Reply #6 on: July 20, 2016, 10:02:56 AM »
Hey Matt,

that makes sense! Thanks a lot for the update and looking forward to try the changes :)

Offline ASK51

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Re: Beta 4 - Preview unlike render.
« Reply #7 on: July 21, 2016, 08:28:46 AM »
Hey Matt,

I did some more testing, and I just wanted to suggest to always use the GI solution that is used for the final render ;)

The one in the preview always adds some yellowness to the image even if there is nothing in the light and atmosphere settings telling it to be yellow. So if you want to have a neutral sky and would render the final output with the GI solution from the preview, I would expect to get the yellow in the final image as well. Since all settings are set to either white or blue, its really hard to counter that behavior even if both images are consistent with each other.

But yeah...thats really just my suggestion :)

Offline ASK51

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Re: Beta 4 - Preview unlike render.
« Reply #8 on: October 06, 2016, 02:34:03 PM »
Hey again,

I was just curious, since I saw there was a small update to the TG4 release version, how things are going on the side of the GI engines used on RTP vs. Render. Didnt see any changes here in the patch notes so I wanted to ask if this is still planned for like the next patch or something like that.

I am working on some Sunset stuff now and the color inaccuracy is so strong in that particular case that its basically impossible to predict the outcome of the render :(

Any estimate on this would be highly appreciated :)

Offline Matt

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Re: Beta 4 - Preview unlike render.
« Reply #9 on: October 06, 2016, 05:46:13 PM »
I plan to have a solution to this (although maybe not a perfect solution) in 4.1, which is targeted for a December release.

Matt
Just because milk is white doesn't mean that clouds are made of milk.

Offline EwanD

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Re: Beta 4 - Preview unlike render.
« Reply #10 on: May 05, 2017, 09:14:59 AM »
Hi Matt! i'm having similar issues  with differences in the preview and final renders. I'm just wondering if the option to render final atmospheres with the same GI as the RTP is available somewhere?
I generally prefer the results of the RTP in terms of the tonal balancing and GI and it would be great to be able to match this if needed sometimes,

http://www.planetside.co.uk/forums/index.php/topic,21728.msg218519.html#msg218519 i've posted here as well but KlausK pointed me over to this thread.

thanks for your help!

Thanks for posting those examples. I think it's probably due to the different GI engines used for atmosphere by the RTP and final renders. I could address this by having an option to render final atmospheres with the same GI engine as the RTP, or making the RTP converge towards the same GI as the final renders. I'll try to do one or both of these things for 4.0 or 4.1.

Matt

 

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