Better to underexpose or overexpose? - Page 2 at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > Open DV Discussion

Open DV Discussion
For topics which don't fit into any of the other categories.


Reply
 
Thread Tools Search this Thread
Old December 13th, 2007, 08:10 AM   #16
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
OVEREXPOSE doesn't mean blow the highlights! Blown highlights are gone forever. That's why it's so critical to use a 3 channel histogram. A lightmeter will tell you you're OK when one color channel is blown.
Bill Ravens is offline   Reply With Quote
Old December 13th, 2007, 01:09 PM   #17
Trustee
 
Join Date: Dec 2006
Location: Little Rock
Posts: 1,383
Sometimes the correct answer is not what your were looking for.

You asked if it was better to over expose SD video or under expose SD video and fix in post.
The correct answer is neither. It is better to expose SD video properly when shooting by using industry standard measurement tools, like a light meter, waveform monitor, vector scope, or simply using the built-in zebra bars on your camera.

Nothing was said in your first post about how much time or money you had for a shoot.

It's kind of like rebuilding an engine and asking if it is best to under tighten the bolts, or over tighten the bolts. The correct answer is neither. It's best to tighten the bolts to the recommended torque setting by using industry standard measurement tools, like a torque wrench.
David W. Jones is offline   Reply With Quote
Old December 13th, 2007, 02:17 PM   #18
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
Sorry, David, I beg to differ.
Built in light meters do a fair job of determining proper exposure, however, it's not necessarily optimum exposure. In the context of getting the most image information recorded on your record media, in most cases it is better to expose on the high side of the bandwidth than on the low side. The built in lightmeter won't advise you on the subtleties of how to do this, unless you dial some exposure bias into the reading. This is tricky, however, because the amount of "overexposure" that is truly optimal changes according to the scene characteristics. No averaging meter sees well enough to predict the best, ie optimum exposure for every scene. The meter only shows you what the optimum exposure is for an 18% grey scene. How many perfectly defined 18% gray scenes do you run across on every shoot?

That all being said, one is better off, in digital imaging, to err on the high side, that is to overexpose, as long as the highlights aren't blown. How does one tell if the highlights are blown? A 3 channel histogram is the most accurate way. This is commonly accepted knowledge, not my invention or opinion.

BTW, "standard" torque wrenches can be grossly inaccurate if not used properly. They measure stiction, not true torque as seen by the head of the bolt. There are precision instruments available when the sledgehammer approach isn't close enough.
Bill Ravens is offline   Reply With Quote
Old December 13th, 2007, 04:08 PM   #19
Inner Circle
 
Join Date: Aug 2005
Location: Atlanta/USA
Posts: 2,507
Quote:
Originally Posted by Roy Beazley View Post
As far as zebras go I like to see them only on the brightest highlights and maybe spread over some to the next level up... but it depends on your camera.
Where do you set your zebras? 80%? 90%? or 100%?
__________________
Ervin Farkas, CDVS
Certified Legal Videographer
Ervin Farkas is offline   Reply With Quote
Old December 13th, 2007, 07:47 PM   #20
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
100% means it's clipping info. Not much clearer decision point than that.
Bill Ravens is offline   Reply With Quote
Old December 13th, 2007, 08:00 PM   #21
Inner Circle
 
Join Date: Jun 2003
Location: Toronto, Canada
Posts: 4,750
Most cameras usually don't clip at 100%. They will record a little headroom above that. On particular cameras you can set that clipping level.

2- I highly suggest you do your own tests.

If you expose very bright, the detail will first hit the camera's knee circuit and then it will clip. The behaviour of the knee differs between cameras and depends on menu settings.

If you expose too dark, bringing up exposure in post will increase noise.

Color correction/grading also plays a role in this.

3- Learn your camera. Learn how the zebras + what you see in the viewfinder and monitor correspond to your exposure level. Some zebras can be set between 70~100... this makes a difference obviously.
Glenn Chan is offline   Reply With Quote
Old December 13th, 2007, 08:16 PM   #22
Regular Crew
 
Join Date: May 2004
Location: tampa fl
Posts: 92
Quote:
Originally Posted by Bill Ravens View Post
OVEREXPOSE doesn't mean blow the highlights! Blown highlights are gone forever. That's why it's so critical to use a 3 channel histogram. A lightmeter will tell you you're OK when one color channel is blown.
So where would you get one of these and could it connect to the H1? That would be cool :)

Thanks
Tony
Roy Beazley is offline   Reply With Quote
Old December 13th, 2007, 09:06 PM   #23
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
Only place I know of would be to use Adobe Audition(aka Serious Magic's HD Rack). Unfortunately, Adobe wants an arm and a leg for it. And that means you have to lug a laptop around to make it work. Some of the newer cameras, like the EX1, have built in histograms, but, the video camera makers still haven't wigged to the fact that a monochrome histogram is not the whole story, you need a 3 channel histogram, because you can blow one channel and the mono histogram won't show it.
Bill Ravens is offline   Reply With Quote
Old December 14th, 2007, 12:36 AM   #24
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Er- um - I think you meant On Location, now from Adobe, formerly Serious Magic.
Jim Andrada is offline   Reply With Quote
Old December 14th, 2007, 08:33 AM   #25
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
Thanx Jim. Hard to care much about the long fingers of adobe.
Bill Ravens is offline   Reply With Quote
Old December 14th, 2007, 06:49 PM   #26
Regular Crew
 
Join Date: May 2004
Location: tampa fl
Posts: 92
...guess I'll just keep riding the zebras.....lol
Roy Beazley is offline   Reply With Quote
Old December 14th, 2007, 07:08 PM   #27
Regular Crew
 
Join Date: May 2004
Location: tampa fl
Posts: 92
Quote:
Originally Posted by Ervin Farkas View Post
Where do you set your zebras? 80%? 90%? or 100%?
I shot last week on 85%.....
Roy Beazley is offline   Reply With Quote
Old December 15th, 2007, 03:45 AM   #28
Major Player
 
Join Date: Dec 2005
Location: Lanark,Scotland
Posts: 736
Quote:
Originally Posted by David W. Jones View Post
You asked if it was better to over expose SD video or under expose SD video and fix in post.
The correct answer is neither.
I get your point, you sound like someone who has a strict way of working which is fine , each to their own. Personally i never have the time to set up waveform monitors and i think using a light meter with digital is pointleless because unlike film you can see in the viewfinder or monitor the image you are getting.

To answer the origional question.....I went to a lot of seminars at the Edinburgh film festival this year and one of them was a post digital grading company, they had examples of work and had their grading desk at the front of the auditorium. They said it is best IF ANYTHING to underexpose slightly, now of course as David said its better to expose correctly but once highlights have blasted out they are gone. (there, you heard it from the horses mouth)

The botom line is if you are going to do anything other than expose correctly (the correct exposure being the farthest you can go without anything blasting out) then you should underexpose slightly as this can be fixed unlike overexposure.

Having said that I personally dont even use zebras, i judge the image by eye and iv never had any problems.

Andy.
__________________
Actor: "where would that light be coming from?"
DP: "same place as the music" -Andrew Lesnie-

Last edited by Andy Graham; December 15th, 2007 at 05:25 AM.
Andy Graham is offline   Reply With Quote
Old December 15th, 2007, 09:58 AM   #29
Trustee
 
Join Date: Dec 2006
Location: Little Rock
Posts: 1,383
Quote:
Originally Posted by Andy Graham View Post
I think using a light meter with digital is pointless because unlike film you can see in the viewfinder or monitor the image you are getting.
I guess I'm just an old school fool. Before I ever pull a camera out of it's case, I use my light meter and color temp meter to instantly check exposure level, lighting ratios, and color temperature.
David W. Jones is offline   Reply With Quote
Old December 15th, 2007, 10:37 AM   #30
 
Join Date: Nov 2001
Location: santa fe, nm
Posts: 3,264
Images: 10
to rely on what you see in the viewfinder is a fool's errand. the viewfinder has brightness and contrast controls that completely negate any accurate representation of the real image lighting. The only time I would rely on a viewfinder for anything but framing is when it's a reflex image.
time and time again, in this business, I run into people who are so completely stuck in their belief system that they can't accept the latest technological truths. Actually just means more business for me, so have at it.

roy....

there are very valid reasons for shooting at zebra settings other than 100%. For example, skin tends to expose around 70%. Setting the zebra for 70% and exposing to just remove zebra from skin works very well when the subject is primarily a talking head.
Bill Ravens is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > Open DV Discussion

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 05:17 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network