photo gray card?
- Thread starter powerdog
- Start date
Barry_Green
Moderator
Re: photo gray card?
There was a long discussion about using a gray card for white balancing here a few months ago, you might be able to find it with the search function.
Basically though, an 18% gray card isn't for white balance, it's for exposure. 18% gray, as seen by a spot meter, shoud approximate about how an incident meter would report exposure.
There was a long discussion about using a gray card for white balancing here a few months ago, you might be able to find it with the search function.
Basically though, an 18% gray card isn't for white balance, it's for exposure. 18% gray, as seen by a spot meter, shoud approximate about how an incident meter would report exposure.
XCheck
Veteran
Re: photo gray card?
Since 18% grey card is (should be) a neutral grey, it can be used for white balancing if you overexpose it (open the iris so you get 100 IRE), and then set the WB. Then you have to set a correct exposure, though. I've seen some saying 18% grey should be about 45 IRE but I think it should be more like 50. That was you have a little more lattitude for highlights than shadows.
Anyone has an opinion on that?
Since 18% grey card is (should be) a neutral grey, it can be used for white balancing if you overexpose it (open the iris so you get 100 IRE), and then set the WB. Then you have to set a correct exposure, though. I've seen some saying 18% grey should be about 45 IRE but I think it should be more like 50. That was you have a little more lattitude for highlights than shadows.
Anyone has an opinion on that?
TC
Resident Agitator
Re: photo gray card?
[quote author=J_Barnes link=board=lighting;num=1096037270;start=0#2 date=09/24/04 at 12:34:35]Green grass is also typically close to 18% grey when shooting monochromatic. Just as a sidenote.[/quote]
Ooh, look at me, I'm James Barnes, I know SO MUCH about film... ooh!!
I WAS JOKING!!! ONLY JOKING!!! It just took my by suprise that you knew something that obscure.
[quote author=J_Barnes link=board=lighting;num=1096037270;start=0#2 date=09/24/04 at 12:34:35]Green grass is also typically close to 18% grey when shooting monochromatic. Just as a sidenote.[/quote]
Ooh, look at me, I'm James Barnes, I know SO MUCH about film... ooh!!
I WAS JOKING!!! ONLY JOKING!!! It just took my by suprise that you knew something that obscure.
THiNSPiRiT
Well-known member
Re: photo gray card?
HAHAHAHA... TC, you're pure jokes... Barnes, that is quite the obscure bit of knowledge...
HAHAHAHA... TC, you're pure jokes... Barnes, that is quite the obscure bit of knowledge...
J_Barnes
Veteran
Re: photo gray card?
Obscure knowledge? Ha...
The first commercial VCR was a big machine called the VERA and it recorded on gigantic six foot-tall spools of magnatized steel tape...BUT... in order to record the massive (in thos days) amount of information in a 30 fps video picture, it had to operate at a transport speed of 225 miles per hour!
Because of the physical requirements of the transport speed, the tape was made of solid steel, and the machine had to be installed in a re-enforced steal bunker because it was essentially an open-air bandsaw. If there ever was a tape break (which there were), it would easily slaughter anything in the room with flailing razor thin tape flying at hundreds of miles an hour.
As you can see, the machine was a miserable failure and wasn't accepted in the industry, causing engineers to devise a method to record more information at a slower transport speed.
And that folks, is how we invented Helical Scanning.
Obscure knowledge? Ha...
The first commercial VCR was a big machine called the VERA and it recorded on gigantic six foot-tall spools of magnatized steel tape...BUT... in order to record the massive (in thos days) amount of information in a 30 fps video picture, it had to operate at a transport speed of 225 miles per hour!
Because of the physical requirements of the transport speed, the tape was made of solid steel, and the machine had to be installed in a re-enforced steal bunker because it was essentially an open-air bandsaw. If there ever was a tape break (which there were), it would easily slaughter anything in the room with flailing razor thin tape flying at hundreds of miles an hour.
As you can see, the machine was a miserable failure and wasn't accepted in the industry, causing engineers to devise a method to record more information at a slower transport speed.
And that folks, is how we invented Helical Scanning.
J_Barnes
Veteran
Re: photo gray card?
[quote author=TC link=board=lighting;num=1096037270;start=0#4 date=09/29/04 at 23:48:53]
Ooh, look at me, I'm James Barnes, I know SO MUCH about film... ooh!!
I WAS JOKING!!! ONLY JOKING!!! It just took my by suprise that you knew something that obscure.[/quote]
By the way, that comes from still photography books. Apparently, red brick walls are also 18% grey as far as monochromatic film is concerned.
[quote author=TC link=board=lighting;num=1096037270;start=0#4 date=09/29/04 at 23:48:53]
Ooh, look at me, I'm James Barnes, I know SO MUCH about film... ooh!!
I WAS JOKING!!! ONLY JOKING!!! It just took my by suprise that you knew something that obscure.[/quote]
By the way, that comes from still photography books. Apparently, red brick walls are also 18% grey as far as monochromatic film is concerned.
andy_starbuck
Well-known member
Re: photo gray card?
I read a discussion about this recently. The recommendation is to use a white card to set the white balance and then use an 18% gray card to begin setting the exposure. The explanation was that if the frame is dominated by something too dark or too light, the automatic exposure would be slightly skewed to overexpose or underexpose the scene, respectively. Using the grqy card brings the automatic exposure to a standard repeatable level. After that it was suggested to use zebra to further adjust the exposure and bring down the overexposed elements in the scene. And then, in the manual, it says if you are using CineLike, to reduce the F-stop by 1/2 (slightly overexposed) to get the full film-look effect.
Andy
I read a discussion about this recently. The recommendation is to use a white card to set the white balance and then use an 18% gray card to begin setting the exposure. The explanation was that if the frame is dominated by something too dark or too light, the automatic exposure would be slightly skewed to overexpose or underexpose the scene, respectively. Using the grqy card brings the automatic exposure to a standard repeatable level. After that it was suggested to use zebra to further adjust the exposure and bring down the overexposed elements in the scene. And then, in the manual, it says if you are using CineLike, to reduce the F-stop by 1/2 (slightly overexposed) to get the full film-look effect.
Andy