Auto Gain Setting at DVinfo.net

ronluc8667 · November 5th, 2002, 03:51 PM

2 Questions

#1
I read on a previous thread the XL1s, in Auto Gain mode, does
not go beyond +12. Is this true?

#2
I have two XL1s cameras. Both configured exactly the same in setup and during the shoot. I film many subjects with both cameras but from different angles. When I view the footage between the two cameras, one is noticably cleaner than the other. The one that is dirtier is also a little brighter. It's not horrible, but noticable. So my question is "Is this normal, or do I have a problem with the dirtier camera"? I have adjusted the setup settings on both cameras to make them look more alike, and I believe I have achieved it. I just want to find out if I should have Canon make adjustments on the dirtier camera.

Thanks,
Ron

Jeff Donald · November 5th, 2002, 04:05 PM

It is difficult for me to comment on the need for adjusting your camera without being able to see the image. I would at the very least call Canon support and talk to them about your impressions. If you're still in warranty I would definitely send it in before the end of the warranty period.

Jeff

Don Palomaki · November 5th, 2002, 06:54 PM

+12 relative to what?

The max 'meter' reading on the XL1 is 0 dB. AGC mode will try to keep the average record level at around -12 dB relative to max allowable digital record level, subject to available gain. Peaks/transients will go beyond -12 dB, and very fast, loud transients may reach 0 dB.

Jeff Donald · November 5th, 2002, 10:30 PM

Don,

I think he is referring to Video gain, not audio, but I could be wrong.

Jeff

Andre De Clercq · November 6th, 2002, 05:05 AM

It's quite possible that the XL1 limits the extra gain-up (w.r.t. the ref gain) in auto mode. There are more cams doing this in order to avoid the "dark" scene taken in auto mode to look allways
"bright" ( and super noisy!)
How do you compare the differences in image quality between yr two cams?. Split screen, side by side monitors...? Compare on test paterns, not on different views, before sending back yr cam.

ronluc8667 · November 6th, 2002, 09:31 AM

Sorry I wasn't clear earlier, but video gain was what I was referring to - not audio.

In playing around with low light settings in my house last night, I compared the setting for gain from Auto to +12 and they seem to look the same. No matter what I do to make it darker in the room, Auto and +12 seem very close if not the same. My point here is that I can't compare Auto to +18 or +30 because Auto never seems to let the gain get that high. I did this test since I read here that someone had mentioned Auto never went beyond +12. I'm not sure where he found this info, but I think he was right.

By the way, this isn't a complaint, just an observation.

Ron

John Klein · November 6th, 2002, 09:47 PM

I'm sorry for offending you, but I can't figure out why someone with $7,000+ invested in making video is using Auto??????

That being said, I shoot a 1S in manual but a pd150 in auto. :)

They don't always match too well, but the 1S is used for tight shots and the 150 for wide ones which IMO needs to take A LOT of other image information (foreground, background, etc.) into account.

When you are in auto, the entire image is metered and then the cam makes the exposure adjustments. Since you are shooting different angles, the brightness of the image is varied which is why, I think, you get different exposures.

Even if you were shooting the same angle, but different focal lengths (one is tight and one is wide), you're going to see differences because the images are going to be taking more or less of the background or what the subject's clothes into account.

Shooting subjects with white or black backgrounds will play a lot of havoc with Auto exposures. Let's say you've got one cam and two side by side subjects, a bride in white and a groom in black for instance.

In auto if you zoom in tight, and pan from the bride to the groom, you'r going to get wildly different exposures, as the meter is just trying to make everything, a middle grey (50% between light and dark).

Try finding the proper exposure in manual, manual WB each from the same angle, set both cams identically and then shoot. See if you still see the difference? Then position each cam where you want and see if you get the results you need. Let us know how it goes.

November 6th, 2002, 09:47 PM	#7
John Klein Regular Crew Join Date: Dec 2001 Location: Wisconsin, USA Posts: 182	I'm sorry for offending you, but I can't figure out why someone with $7,000+ invested in making video is using Auto?????? That being said, I shoot a 1S in manual but a pd150 in auto. :) They don't always match too well, but the 1S is used for tight shots and the 150 for wide ones which IMO needs to take A LOT of other image information (foreground, background, etc.) into account. When you are in auto, the entire image is metered and then the cam makes the exposure adjustments. Since you are shooting different angles, the brightness of the image is varied which is why, I think, you get different exposures. Even if you were shooting the same angle, but different focal lengths (one is tight and one is wide), you're going to see differences because the images are going to be taking more or less of the background or what the subject's clothes into account. Shooting subjects with white or black backgrounds will play a lot of havoc with Auto exposures. Let's say you've got one cam and two side by side subjects, a bride in white and a groom in black for instance. In auto if you zoom in tight, and pan from the bride to the groom, you'r going to get wildly different exposures, as the meter is just trying to make everything, a middle grey (50% between light and dark). Try finding the proper exposure in manual, manual WB each from the same angle, set both cams identically and then shoot. See if you still see the difference? Then position each cam where you want and see if you get the results you need. Let us know how it goes. __________________ < >< . . . . . < >< . . . . . < ><

November 5th, 2002, 03:51 PM	#1
ronluc8667 Regular Crew Join Date: Jan 2002 Location: Colorado Posts: 31	Auto Gain Setting 2 Questions #1 I read on a previous thread the XL1s, in Auto Gain mode, does not go beyond +12. Is this true? #2 I have two XL1s cameras. Both configured exactly the same in setup and during the shoot. I film many subjects with both cameras but from different angles. When I view the footage between the two cameras, one is noticably cleaner than the other. The one that is dirtier is also a little brighter. It's not horrible, but noticable. So my question is "Is this normal, or do I have a problem with the dirtier camera"? I have adjusted the setup settings on both cameras to make them look more alike, and I believe I have achieved it. I just want to find out if I should have Canon make adjustments on the dirtier camera. Thanks, Ron

November 5th, 2002, 04:05 PM	#2
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	It is difficult for me to comment on the need for adjusting your camera without being able to see the image. I would at the very least call Canon support and talk to them about your impressions. If you're still in warranty I would definitely send it in before the end of the warranty period. Jeff

November 5th, 2002, 06:54 PM	#3
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,489	+12 relative to what? The max 'meter' reading on the XL1 is 0 dB. AGC mode will try to keep the average record level at around -12 dB relative to max allowable digital record level, subject to available gain. Peaks/transients will go beyond -12 dB, and very fast, loud transients may reach 0 dB.

November 5th, 2002, 10:30 PM	#4
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	Don, I think he is referring to Video gain, not audio, but I could be wrong. Jeff

November 6th, 2002, 05:05 AM	#5
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	It's quite possible that the XL1 limits the extra gain-up (w.r.t. the ref gain) in auto mode. There are more cams doing this in order to avoid the "dark" scene taken in auto mode to look allways "bright" ( and super noisy!) How do you compare the differences in image quality between yr two cams?. Split screen, side by side monitors...? Compare on test paterns, not on different views, before sending back yr cam.

November 6th, 2002, 09:31 AM	#6
ronluc8667 Regular Crew Join Date: Jan 2002 Location: Colorado Posts: 31	Sorry I wasn't clear earlier, but video gain was what I was referring to - not audio. In playing around with low light settings in my house last night, I compared the setting for gain from Auto to +12 and they seem to look the same. No matter what I do to make it darker in the room, Auto and +12 seem very close if not the same. My point here is that I can't compare Auto to +18 or +30 because Auto never seems to let the gain get that high. I did this test since I read here that someone had mentioned Auto never went beyond +12. I'm not sure where he found this info, but I think he was right. By the way, this isn't a complaint, just an observation. Ron