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View Full Version : Forcing Linear renders exposure adds a lot of grain! Linear workflow suggested?



Netvudu
06-20-2011, 08:28 PM
Hi there.

I understand quite clearly by now the advantages of Linear Workflow, and how to use it in LW 10 (which is a no-brainer. Thanks devs)

Now, Ive noticed that if I render something in LW9 and it looks terribly dark, I can add a gamma correction in post. This will obviously look wrong because Im getting the wrong colors (due to double gamma correction of textures), and it will probably burn my whitest points in the image. I understand that. But it might end up looking okay-ish if a bit washed out (which is typical from the double correction).

Now, Im a bit puzzled because when I open the same scene in LW10, the scene looks very nice in my gamma corrected VPR, and if I render to Linear and go to Fusion and add a 2.2 gamma correction it looks more or less like the VPR, but then I decide its still a bit darker than the double-corrected gamma version from LW9, and I crank the gamma even higher and suddenly I start to get a huge amount of noise! Im working with OpenEXR files, of course, so its not a bit depth problem.

So, I learn from this that I cannot crank up the gamma values above 2.2 in Fusion (for SRGB textures) because I get too much noise...would somebody explain me the exact reason? Also, does this mean I will have to be reasonably happy with my lighting in LW because I wont be able to crank it up above the 2.2 value in Fusion?
Its all still a bit new so I would love to know a bit more about your lighting workflows for linear color space...

Greenlaw
06-20-2011, 08:55 PM
Not sure if this is the noise your seeing but look under the Processing tab and check that Default Dither Intensity and Dither Intensity are both set to Off. For some reason, we occasionally find one or both of these options switched to Normal, in which case Lightwave renders a noise pattern over the entire image. Even worse, it's a tiled noise pattern, and it sometimes hoses our renders when compositing in float space. The pattern is typically not visible until you crank up the gamma.

We have to keep reminding our artists to double-check that these options are set to Off. My suspicion is that 'Normal' is a default setting and when we get a new guy in the shop, the default setting creeps back into our pipeline like virus. It's been like this for years. :(

G.

Red_Oddity
06-21-2011, 03:17 AM
Disable dither, as has been suggested, use the gamma corrected AA pixel filter technique as explained on the forum as well.
In post don't push gamma too much beyond what it should be, better yet, set gamma as it should be (2.2 in your case) and set black and white points instead (or tweak the gain, which pretty much acts like an exposure control would)

lardbros
06-21-2011, 03:26 AM
Not sure if this is the noise your seeing but look under the Processing tab and check that Default Dither Intensity and Dither Intensity are both set to Off. For some reason, we occasionally find one or both of these options switched to Normal, in which case Lightwave renders a noise pattern over the entire image. Even worse, it's a tiled noise pattern, and it sometimes hoses our renders when compositing in float space. The pattern is typically not visible until you crank up the gamma.

We have to keep reminding our artists to double-check that these options are set to Off. My suspicion is that 'Normal' is a default setting and when we get a new guy in the shop, the default setting creeps back into our pipeline like virus. It's been like this for years. :(

G.

Yup, 'normal' is the default... i didn't even realise this setting had crept in at all, it's hideous!! They say it gets rid of banding, but hey... give me banding any day of the week! Have you tried the dithering on higher settings? :D It's hilarious!!!

Lightwolf
06-21-2011, 04:29 AM
I keep re-posting this, but what the heck... ;)

Just as a heads up:
Buffer savers (which are essentially image filters) are not affected by the dithering at all. The dithering is applied after image filters (before the saver designated in the render globals is used).

Cheers,
Mike

Netvudu
06-21-2011, 05:10 AM
Oh my god! Youre right guys. Its the evil "dither" setting creeping into my renders. Thanks. That solved it.

Greenlaw
06-21-2011, 09:06 AM
Yup, 'normal' is the default... i didn't even realise this setting had crept in at all, it's hideous!! They say it gets rid of banding, but hey... give me banding any day of the week! Have you tried the dithering on higher settings? :D It's hilarious!!!
Yes, this was for improving rendering back in the days when cavemen chiseled their pixels in 8-bits per channel on stone tablets. Not sure why this is still the 'default' setting. :)

G.

funk
06-21-2011, 09:07 AM
Yep the LW dither is nasty looking. If you want to see dither done right/better:

Just take an exr that has banding into photoshop and apply an ADD NOISE filter at 0.10% / gaussian / monochrome.

The banding goes away, but the dither can't be seen. Newtek need to "borrow" the same options/settings :)

I made a feature request: http://www.newtek.com/forums/showthread.php?t=120258

pixelranger
06-21-2011, 10:42 AM
Be aware that gamma shouldn't be used heavily as colour correction. Use it in Fusion to see how much brighter you need the renders (or even better, use exposure or gain. If you need to "wash" it out using gamma it is probably a sign that you need another fill light or two, or ambient light). And then feed those values back into your next round of LW renders.

And LW 9 didn't have the linear workflow, so if you were rendering linear images (which you were) for gamma'ing up in post, you should have linearized your textures (in PS or using the image controls in LW) so that both textures and the internal renders were in linear colour space. Then you can lift it all back to srgb, or whatever your output would be, in comp.

Another reason why renders appear grainy using linear workflow, might be because the adaptive antialiasing determines the AA thresholds on that "dark" image and the darkest parts go "unnoticed" by the AA algorithm, and then the lin2srgb conversion in post makes those values in the dark areas much more visible.

geo_n
06-21-2011, 11:29 AM
I keep re-posting this, but what the heck... ;)

Just as a heads up:
Buffer savers (which are essentially image filters) are not affected by the dithering at all. The dithering is applied after image filters (before the saver designated in the render globals is used).

Cheers,
Mike

Does this mean i dont have to turn off dither when using exrtrader?

Sensei
06-21-2011, 11:32 AM
Dithering is done when floating point value is converted to 8 bit integer RGBA. Dithering simulates lacking of precision of integers.

Lightwolf
06-21-2011, 11:32 AM
Does this mean i dont have to turn off dither when using exrtrader?
Yes... No need to turn it off.
I found out when I implemented the limited region/data window feature.

Cheers,
Mike

Lightwolf
06-21-2011, 11:34 AM
Dithering is done when floating point value is converted to 8 bit integer RGBA. Dithering simulates lacking of precision of integers.
Except that LW dithers the fp values prior to saving using the globals.
It's not even dithering but adding pseudo-random noise.

Cheers,
Mike