Low Noise in Spotlight Mode at DVinfo.net

Jonathan Gentry · March 28th, 2007, 09:28 PM

I am wondering how the spotlight mode achieves such low noise. Sometimes you don't need to resolve shots in dark areas. You just want them to be dark and clean. So how does the spotlight mode achieve dark shots with such low noise? Can it be duplicated in other standard modes?

-Jonathan

Chris Hurd · March 28th, 2007, 09:39 PM

Hi Jonathan, my understanding of spotlight mode is that it uses a different metering process, which exposes only for the center of the image and simply ignores the surrounding areas (which keeps faces from blowing out; usually an evaluative metering will try to balance the entire frame, resulting in overexposed faces and noisy backgrounds). I've never tried to duplicate it in any of the other program modes but maybe somebody else has around here.

Jonathan Gentry · March 28th, 2007, 10:39 PM

Yes but all metering aside (try in full manual mode any settings you wish) I can't get as noise free an image in any mode with any settings as I can with spotlight mode when there is next to no light. How is this done? It's a stark difference.

Cesar Ruiz · March 29th, 2007, 10:33 AM

Hmm, I was able to replicate it using -3db Gain on Manual. Granted I was verifying using the magnification function. I did not have it hooked up to an HDTV.

Don Palomaki · March 29th, 2007, 07:33 PM

Not sure about the A1, but the older XL1 and GL1 models use a bottom center weighted average metering scheme for normal exposure modes, and for SPOTLIGHT mode they used a "49-area-splitting evaluation photometry" scheme (7x7 zones). I suspect that it looks for the brightest zones and average meters on that zone. Thus the bright areas in the spot light receive a "correct" exposure, and that means the areas out of the spotlight would have less noise-producing exposure components (e.g., lower gain, faster shutter) and thus noise in the shadows would be less and shadows would be darker effectively more of a Black Press effect perhaps.

The A1 may use a similar system, possibly with more zones and there may be other image processing involved as well.

Jonathan Gentry · March 29th, 2007, 08:09 PM

OK, but here's what I'm getting at (and I would like someone else to try this.) When I hook up my A1 to my HDTV through the included HD cable and preview the screen (in a fairly dimly lit living room) I can't reproduce the low amount of noise in Spotlight mode with any other mode by changing aperature, shutter or any other setting in that mode. Can somone else test this? Maybe there is a setting I'm missing that would allow me to reproduce? I get a pretty noisy shot in every other mode with the gain switch all the way down.

Richard Hunter · March 29th, 2007, 09:54 PM

Hi Jonathan. Is it possible that your AGC switch is set to ON and that this is not active in spotlight mode? Just a thought.

Richard

Jonathan Gentry · March 29th, 2007, 11:10 PM

Thank you sir. Yes the AGC button was on. I was thinking that this cam couldn't possibly be this noisy.

Problem solved...

David McGiffert · March 29th, 2007, 11:39 PM

Wow Richard...nice one.

David

March 28th, 2007, 09:28 PM	#1
Jonathan Gentry Regular Crew Join Date: Jun 2004 Posts: 183	Low Noise in Spotlight Mode I am wondering how the spotlight mode achieves such low noise. Sometimes you don't need to resolve shots in dark areas. You just want them to be dark and clean. So how does the spotlight mode achieve dark shots with such low noise? Can it be duplicated in other standard modes? -Jonathan

March 28th, 2007, 09:39 PM	#2
Chris Hurd Obstreperous Rex Join Date: Jan 2001 Location: San Marcos, TX Posts: 27,368 Images: 513	Hi Jonathan, my understanding of spotlight mode is that it uses a different metering process, which exposes only for the center of the image and simply ignores the surrounding areas (which keeps faces from blowing out; usually an evaluative metering will try to balance the entire frame, resulting in overexposed faces and noisy backgrounds). I've never tried to duplicate it in any of the other program modes but maybe somebody else has around here. __________________ CH Search DV Info Net \| 20 years of DVi \| ...Tuesday is Soylent Green Day!

March 29th, 2007, 10:33 AM	#4
Cesar Ruiz Regular Crew Join Date: Feb 2003 Location: Manchester, NH Posts: 182	Hmm, I was able to replicate it using -3db Gain on Manual. Granted I was verifying using the magnification function. I did not have it hooked up to an HDTV. __________________ Cana Video Productions, LLC Manchester, NH

March 29th, 2007, 07:33 PM	#5
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	Not sure about the A1, but the older XL1 and GL1 models use a bottom center weighted average metering scheme for normal exposure modes, and for SPOTLIGHT mode they used a "49-area-splitting evaluation photometry" scheme (7x7 zones). I suspect that it looks for the brightest zones and average meters on that zone. Thus the bright areas in the spot light receive a "correct" exposure, and that means the areas out of the spotlight would have less noise-producing exposure components (e.g., lower gain, faster shutter) and thus noise in the shadows would be less and shadows would be darker effectively more of a Black Press effect perhaps. The A1 may use a similar system, possibly with more zones and there may be other image processing involved as well. __________________ dpalomaki@dspalomaki.com

March 29th, 2007, 08:09 PM	#6
Jonathan Gentry Regular Crew Join Date: Jun 2004 Posts: 183	OK, but here's what I'm getting at (and I would like someone else to try this.) When I hook up my A1 to my HDTV through the included HD cable and preview the screen (in a fairly dimly lit living room) I can't reproduce the low amount of noise in Spotlight mode with any other mode by changing aperature, shutter or any other setting in that mode. Can somone else test this? Maybe there is a setting I'm missing that would allow me to reproduce? I get a pretty noisy shot in every other mode with the gain switch all the way down. Last edited by Jonathan Gentry; March 29th, 2007 at 09:41 PM.

March 28th, 2007, 10:39 PM	#3
Jonathan Gentry Regular Crew Join Date: Jun 2004 Posts: 183	Yes but all metering aside (try in full manual mode any settings you wish) I can't get as noise free an image in any mode with any settings as I can with spotlight mode when there is next to no light. How is this done? It's a stark difference.

March 29th, 2007, 09:54 PM	#7
Richard Hunter Trustee Join Date: Dec 2004 Location: Lipa City Batangas, Philippines Posts: 1,110	Hi Jonathan. Is it possible that your AGC switch is set to ON and that this is not active in spotlight mode? Just a thought. Richard

March 29th, 2007, 11:10 PM	#8
Jonathan Gentry Regular Crew Join Date: Jun 2004 Posts: 183	Thank you sir. Yes the AGC button was on. I was thinking that this cam couldn't possibly be this noisy. Problem solved...

March 29th, 2007, 11:39 PM	#9
David McGiffert Regular Crew Join Date: Feb 2007 Location: Topanga, CA Posts: 139	Wow Richard...nice one. David