Noise

L

LeavingTheCandy

Well-known member
Did a shoot a few weeks ago with green screen. (lit properly, etc.)
The green is SOOO noisy, Keylight will not key it. This is the first green I shot with my EX1R. (it's recording to KiPro ProRes 422).

Any ideas? Is this thing just this noisy? I was at -3 gain.

Thanks.
 
That's not enough information to be of any help. There's more to it than shooting at -3 gain.

Posting a brief wouldn't hurt either.
 
And the lighting you used on the green screen as well as the talent. The green screen can have cheap florescent because its going to be green anyway, but there has to be enough light and it has to be relatively even.
 
Well, as for it being too grainy to key, I don't buy it. I've pulled perfect keys with keylight with a 30 dollar greenscreen, lit with 2 halogen worklights, ex1 recording to blocky 35mbps xdcam.

What color temperature are your lights? what did you have to white balance to? did you white balance? When you white balance to yellower light (halogens, work lights, incandescent, etc), the camera compensates by adding gain to the blue channel, giving you noise in your image.

The ideal K you want your ex1 to white balance to is ~5600K, then it's not adding or subtracting any gain from the r g and b channels. When you white balance to something like ~3200k for halogens, the camera is going to have to boost the crap out the blue channel to make the recorded image white balanced, giving you plenty of noticeable noise. This was one of the first problems I ran into when I started shooting seriously, I was also wondering why at -3db it was still so grainy. Picked up some full ctb gels, popped them over the worklights. Cut their output by a stop or so, but the light was perfect 5600k. opened up the aperture a stop or so and enjoyed grain free images.


I'm sure you're familiar with keylight, but a great workflow that works for me for pulling keys off of questionable shots (very, very questionable shots) is setting the output to combined matte, then adjusting the white clip and black clip until the matte is perfect. Usually don't have to mess with anything else, maybe a little bit of preblur.


Hope this helps!
 
Thanks for the great information. I was using a bunch of lights (pro lights...Arri's mostly) but was white balanced to about 3400K. So I guess this explains it.

Your post explains a lot...every time I shoot with my daylight-balanced lights, I love the shots and didn't quite put it together as to why they look so good.

I can not redo this shoot, so I guess I'll have to live with the noise somehow. Any suggestions?

Thanks!
 
Fohdeesha said:
When you white balance to something like ~3200k for halogens, the camera is going to have to boost the crap out the blue channel to make the recorded image white balanced, giving you plenty of noticeable noise.
Click to expand...

I have not found this to be the case in my experience. How do you account for that?
 
Because that is how the circuitry of the camera operates? go do a test with a white wall at different white balances, there has been several threads about this over on dvinfo along with test images. Have a couple 3200/5600 comparisons on my server but it's down at the moment.

Keep in mind "plenty" of noise is all relative, the amount of noise added by the white balance circuitry is nothing compared to noise added by shooting at really high db gain, etc. But when your shooting at -3db and want the cleanest image, the WB circuitry gain is definitely there and will annoy perfectionists
 
I looked at my footage closely and for sure, the Blue channel is noisy as crap. I have to wade through it as this point, but it's CTO and daylight for me from now on!
Any tips for killing noise in the blue?
Thanks.
 
Jay Gladwell said:
I have not found this to be the case in my experience. How do you account for that?
Click to expand...

Well documented, tested, and shown. I never take my cameras off daylight balance any more. As long as the red channel isn't clipping, I'll re-color in post if I have to. It's FAR cleaner to do it that way. I'm actually moving to shooting with a corrective filter on the lens now instead of worrying about doing a white balance.
 
LeavingTheCandy said:
Live and learn. I had never heard of this. Do you run at 5600K? What on-camera filter do you use? I'm all ears.
Thanks.
Click to expand...

Yep, I run at 5600k, and light to that if I can. If not, use 3500K lighting and use a tungsten to daylight filter. The filters you are looking for are:

80A (takes 3200k light to 5500K) or
80B (takes 3500K light to 5500K)

I prefer the 80A as I don't mind having a bit of extra blue in my images. Our cameras are STARVED for blue light in most conditions, but especially when we have tungsten sources. So going a bit cool is just fine by me.

You can find quality filters from Hoya, Tiffen, Heliopan, and others.
 
amen Perrone. You were the one that helped me figure this issue out a year or two ago on dvinfo (Jon Sands)!
 
Thanks! I think I am about to experience a game-changer! I couldn't figure out why my outdoor stuff looked so awesome, while my indoor (3200K) shots looked mediocre, even when lit properly.
Thanks a million!
 
LeavingTheCandy said:
BTW, notice any difference with the filter on the lens vs. gelling the lights?
Thanks.
Click to expand...

On a controlled set, the only difference would be a 1 minute lens filter versus a 10-20 minute lighting gel change. On an ambient light set (outdoors) or with open windows, the lens filter affects ALL light, not just the movie lights. Makes a significant difference. Blue filtering daylight can clip the blue channel, so be careful.
 
Really Perrone? You shoot everything in 5600? Greenscreen and regular footage?

I have done that too when I forgot to switch to WB, and just color corrected because any inside lights make the skin yellow to the max. But I'd like to hear more on your thinking behind this. I have not come across this. Sounds interesting.
 
Chadfish said:
Really Perrone? You shoot everything in 5600? Greenscreen and regular footage?

I have done that too when I forgot to switch to WB, and just color corrected because any inside lights make the skin yellow to the max. But I'd like to hear more on your thinking behind this. I have not come across this. Sounds interesting.
Click to expand...

I have not shot any greenscreen since moving to this, but really, we're just talking about shooting daylight balance. Nothing special about that at all. CRI on daylight balanced footage and lighting is higher than Tungsten so it should HELP greenscreen.

I bulb when I am inside shooting narrative. At least to 3500k so that doesn't really cause me any issues. No more so that shooting during the day with a normal lightbulb on in the house. If you'd like to see WHY I do it this way, it's simple. Go shoot a quick indoor scene with a custom white balance. Then go look at that footage with a viewer that can show the R, G, and B channels separately. Notice how noisy the blue channel is compared to the green. This happens because there simply isn't enough blue light in basic tungsten lighting. So when you do a white balance, all you are really doing is adding gain (and noise) to the blue channel. By staying on daylight, you aren't adding any gain, and it's up to YOU to boost the blue levels appropriately. Once this is done, you should get a lot more balanced light hitting that sensor and a lot less noise.
 
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