Grey card? Why?


Status
Not open for further replies.

unseen

Senior Member
Dec 14, 2004
2,622
0
0
NTU and Wdls
#1
Recently I see more and more (expensive) devices popping up to correct white balance. I see people willing to fork out $50 - $100+ for such devices. I'm simply amazed.

I don't understand, but
1) why are grey cards needed to correct whitebalance?

When i've time, I simply take a photo of a piece of blank white A4 paper, and use it to set custom white balance. It's non reflective, it's portable, and it's very accurate.
When I'm desperate, I simply take a photo of my black bag, and use it to set white balance.
That way, colour purity is maintained. To make it warmer I shoot a piece of very light blue piece of paper, to make it cooler I shoot a slight yellowish piece of paper.

2) Is using a blank A4 paper any less accurate than those expensive devices?

You under expose white and you get a shade of grey.
You overexpose a relative reflective black surface and you get another shade of grey.

From what I understand the idea behind custom WB is simply to balance the different channels to get back equal amounts of Red and Green and Blue. That way, the colour cast is removed (grey is simply a colour where channel R = channel G = channel B)
3) Is there anything wrong with what I'm doing?
4) Is there anything wrong with my understanding of the theory of balancing WB?
 

azul123

Senior Member
Dec 4, 2004
2,776
0
0
Eastern Bloc
#2
Nothing wrong, some just want to be very accurate and don't want to see any colour cast, if you trust your eyes entirely you can use whatever White Balance method. Some don't even want to trust the camera and therefore willing to fork out the money to make sure that they have neutral reflective colour for their White Balance settings.

Some don't even need to do Custom White Balance and shoot in RAW with adjustments in PP, to each his own. Others may just want to try try only mah...

../azul123
 

picorat

New Member
Nov 10, 2006
21
0
0
#3
hi,

i think you got it wrong. grey cards are used for metering purposes, not white balancing.

;)
 

dominator

Senior Member
Mar 7, 2005
1,662
0
0
11
Amazon Forest
#5
Recently I see more and more (expensive) devices popping up to correct white balance. I see people willing to fork out $50 - $100+ for such devices. I'm simply amazed.

I don't understand, but
1) why are grey cards needed to correct whitebalance?

When i've time, I simply take a photo of a piece of blank white A4 paper, and use it to set custom white balance. It's non reflective, it's portable, and it's very accurate.
When I'm desperate, I simply take a photo of my black bag, and use it to set white balance.
That way, colour purity is maintained. To make it warmer I shoot a piece of very light blue piece of paper, to make it cooler I shoot a slight yellowish piece of paper.

2) Is using a blank A4 paper any less accurate than those expensive devices?

You under expose white and you get a shade of grey.
You overexpose a relative reflective black surface and you get another shade of grey.

From what I understand the idea behind custom WB is simply to balance the different channels to get back equal amounts of Red and Green and Blue. That way, the colour cast is removed (grey is simply a colour where channel R = channel G = channel B)
3) Is there anything wrong with what I'm doing?
4) Is there anything wrong with my understanding of the theory of balancing WB?
I think to use a grey card or not depends on individual. I guess majority do not use it?

But yes, it is way too much to pay $50 - $100 for just a piece of card or paper.
 

catchlights

Moderator
Staff member
Sep 27, 2004
21,903
46
48
Punggol, Singapore
www.foto-u.com
#6
any neutral in tone object can use for doing Custom White Balance, be it a piece of white paper, gray card or expodisc.

some device are design to be use in accuracy, like expodisc, so you have to pay a premium for it.
 

arttl

New Member
Jul 20, 2004
1,365
0
0
37
Planet PJ
www.flickr.com
#7
The gray card is usually used when you need to make a light meter reading from a 18% gray surface. In this case, you are making a reflection measurements of incident illumination on the card reflected to the light meter.

Now, i think you are confused with the connection with a gray card to WB. If you ever need to do a custom WB with a gray card, simply turn the card to the white side! I've never heard of gray balance!

A digital shooter will think a gray card is useless. But for flim shooter, the gray card is most helpful to check meter reading especially under the ever-changing lighting situation. (Eg, outdoors)

Hope the above helps.

Jon
 

Oct 30, 2006
252
0
0
#8
To make it warmer I shoot a piece of very light blue piece of paper, to make it cooler I shoot a slight yellowish piece of paper.
THIS IS A GOOD TIP! :thumbsup: Will use it as another option next time, though i can also do the same thing in Photoshop.

Ya, grey card is used for light metering, not white balance.
However, i find grey card a bit troublesome. I might as well just find a pitch black or brightest white in my target subject/environment, then meter and compensate -2 & +2 accordingly. :sweat:
 

Splutter

Senior Member
Dec 28, 2003
2,909
0
0
35
Gim Boon Tai
www.splutterphotography.com
#9
A grey card can still be used for WB correction because it is neutral tone. This means that in the RGB table, R=G=B = whatever value. Pure white is 255 while black is 0. Grey is around 46.
 

lsisaxon

Senior Member
Nov 29, 2004
11,941
0
0
#10
THIS IS A GOOD TIP! :thumbsup: Will use it as another option next time, though i can also do the same thing in Photoshop.

Ya, grey card is used for light metering, not white balance.
However, i find grey card a bit troublesome. I might as well just find a pitch black or brightest white in my target subject/environment, then meter and compensate -2 & +2 accordingly. :sweat:
Looks like a recipe for disaster. The brightest white may be several stops higher than your subject and the darkest black may be several stops lower depending on the dynamic range of the entire scene. I would rather meter on anything else of any other colour that I think may be closest in brightness to 18% grey.
 

lsisaxon

Senior Member
Nov 29, 2004
11,941
0
0
#11
Recently I see more and more (expensive) devices popping up to correct white balance. I see people willing to fork out $50 - $100+ for such devices. I'm simply amazed.

I don't understand, but
1) why are grey cards needed to correct whitebalance?

When i've time, I simply take a photo of a piece of blank white A4 paper, and use it to set custom white balance. It's non reflective, it's portable, and it's very accurate.
When I'm desperate, I simply take a photo of my black bag, and use it to set white balance.
That way, colour purity is maintained. To make it warmer I shoot a piece of very light blue piece of paper, to make it cooler I shoot a slight yellowish piece of paper.

2) Is using a blank A4 paper any less accurate than those expensive devices?

You under expose white and you get a shade of grey.
You overexpose a relative reflective black surface and you get another shade of grey.

From what I understand the idea behind custom WB is simply to balance the different channels to get back equal amounts of Red and Green and Blue. That way, the colour cast is removed (grey is simply a colour where channel R = channel G = channel B)
3) Is there anything wrong with what I'm doing?
4) Is there anything wrong with my understanding of the theory of balancing WB?
Different manufacturer specify different "whiteness" level for their normal A4 paper. You will not get a really correct white. If you don't believe you can use a flash (constant colour temperature) to shoot several brands of A4 paper. Shoot them about 1-2 stops under (depending on what the flash gives you) so that they come out grey. Then you should see some colour difference between them. Plus, they turn yellow with age.. so there's one more unknown.

A grey card is made to be neutral so you will not have these variations.
 

picorat

New Member
Nov 10, 2006
21
0
0
#12
Really? :)

../azul123
yah, really.

the primary purpose of grey card is to meter light.

white balancing is really only an issue in digital workflow*; which really shouldn't even be an issue if you're shooting in raw to begin with.

simple google search on how to use a grey card:
http://www.photography.ca/phototips/meter.html

*yes you have to white balance film too, but not in the way digital does it, which is by custom colour correction.
 

azul123

Senior Member
Dec 4, 2004
2,776
0
0
Eastern Bloc
#13
picorat said:
yah, really.

the primary purpose of grey card is to meter light.

white balancing is really only an issue in digital workflow; which really shouldn't even be an issue if you're shooting in raw to begin with.

simple google search on how to use a grey card:
http://www.photography.ca/phototips/meter.html
I would agree with how traditionally grey card were used before, see what you think about the way they are doing the grey cards such as this one.

http://www.pictureflow.com/products/whibal/index.html

I don't claim to know a lot as I am still learning, but technology has evolved and understandings do change and get realligned as newer discoveries are found.

../azul123
 

Zerstorer

Senior Member
Jul 8, 2002
3,437
0
0
#15
Any colour neutral material can be use for white balancing. White balancing is just re-calibrating the individual colour channels to cancel the imbalance. As long as a material reflects all the channels evenly, it will suffice. Ideally, White, grey, black only differ by the amount of light they reflect(2 1/2stop decrements).

However, it is risky to use black materials as it is far more difficult to visually guage if a "black" material is colour neutral or not compared to a midtone or white object since it reflects far lesser light.

Not all materials reflect light evenly at different angles nor do they behave the same under different types of lightsources, that is why you have the specialized WB tools for a more consistent performance.

Paper by nature is off-white. White paper is created by bleaching and addition of whiteners which as usually bluish. Paper are also graded according to their closeness to true white. So using plain paper u may get varying degrees of accuracy, but it should suffice as long as its close enough.

If one is not picky and does not require absolute accuracy(>90%) of most uses, any reasonably colour neutral surface will do.

There is no right or wrong, just different ways, needs and expectations.
 

Zerstorer

Senior Member
Jul 8, 2002
3,437
0
0
#16
Grey cards are usually easier to take WB measurements with because you can snap a grey card in any auto exposure mode and it will have a decent exposure for an accurate WB reading.

A white card or black card with need correct metering technique or compensation before you get a usable reading.
 

lsisaxon

Senior Member
Nov 29, 2004
11,941
0
0
#17
Any colour neutral material can be use for white balancing. White balancing is just re-calibrating the individual colour channels to cancel the imbalance. As long as a material reflects all the channels evenly, it will suffice. Ideally, White, grey, black only differ by the amount of light they reflect(2 1/2stop decrements).

However, it is risky to use black materials as it is far more difficult to visually guage if a "black" material is colour neutral or not compared to a midtone or white object since it reflects far lesser light.

Not all materials reflect light evenly at different angles nor do they behave the same under different types of lightsources, that is why you have the specialized WB tools for a more consistent performance.

Paper by nature is off-white. White paper is created by bleaching and addition of whiteners which as usually bluish. Paper are also graded according to their closeness to true white. So using plain paper u may get varying degrees of accuracy, but it should suffice as long as its close enough.

If one is not picky and does not require absolute accuracy(>90%) of most uses, any reasonably colour neutral surface will do.

There is no right or wrong, just different ways, needs and expectations.
If one is not picky, then they should just set to Sunny or Cloudy for the WB. It's more consistent.
 

lsisaxon

Senior Member
Nov 29, 2004
11,941
0
0
#18
yah, really.

the primary purpose of grey card is to meter light.

white balancing is really only an issue in digital workflow*; which really shouldn't even be an issue if you're shooting in raw to begin with.

simple google search on how to use a grey card:
http://www.photography.ca/phototips/meter.html

*yes you have to white balance film too, but not in the way digital does it, which is by custom colour correction.
Actually for photography it doesn't really matter because our eyes see things differently each time. People shooting product shots using slides may need to do some colour correction. But the largest user of colour meter is for cine and video. This is because when inter cutting from footage to footage, the colour matching is very important because the eye is able to perceive the relative difference.

However, this is not crucial for photography. Even for a printed photo, the colour is still different under different lighting. If one is really so particular, then they should even take care of the lighting under which the photo is viewed. Just because a feature is there doesn't make it any more important that one need to nitpick about it. I think it is senseless to keep calibrating WB all the time. I don't do that with film (which is also prone to processing variations), there is no reason I should do that with digital as it is very consistent. I find Cloudy WB suits me just fine for almost every situation because it is very close to how the eye perceive the colour at the time of shooting as it retains the original mood.
 

Oct 30, 2006
252
0
0
#19
There are always 2 camps of photographers out there:
One who is TECHNICALLY correct & one who is ARTISTICALLY intense.

The one who is nitpicky about every single detail like a perfect lighting, metering, flash, WB, etc tend to miss out the artistic involvement of every single photo taken. ;) Sometimes, imperfection is a good thing in art. As a designer & aspiring photographer, i am always trying to capture and produce the artistic essence of my work rather than trying to be technically correct. The ends is more important than the means. :lovegrin:
 

unseen

Senior Member
Dec 14, 2004
2,622
0
0
NTU and Wdls
#20
hi,
i think you got it wrong. grey cards are used for metering purposes, not white balancing.
;)
No I didn't. I think you need to read up more. ;)


some device are design to be use in accuracy, like expodisc, so you have to pay a premium for it.
As for expodisc. it's another thing I don't understand.
I understand the theory, it's to average out the various light sources, presenting a somewhat averaged, out of focused image of all incident light.

I've my ways when I don't have anything to do WB on.
Is there anything wrong with simply pointing the lens at the artificial light source, and expose for the light source, throw it out of focus, and use the resultant image for WB? AFAIK you will get 100% pin point accuracy. The main artificial light source would darken everything else in the surrounding, and that small patch of digital "gray" would be more than enough for our cameras to set WB.

In event that there are a few light sources of slightly varying temperature, I simply throw my lens out of focus, include the light sources, and use the "bokeh" for my WB adjustment.
It's 100% as accurate as a expodisc, is it not? any reason it's less accurate?



Not all materials reflect light evenly at different angles nor do they behave the same under different types of lightsources, that is why you have the specialized WB tools for a more consistent performance.
Ah thanks.. I believe this is the point I failed to get, the part about behaving differently under different light sources. Guess I'll explore more on this area.
However, I don't think you need to reflect light evenly. :) given we're looking at a neutral toned image, less light reflected simply = underexposure, and the colour cast is still equally present in the various shades of gray, though severe overexposure => inaccuracy, but from my tests it seems that digital cameras seems to ignore the pure whites and pure blacks while calculating WB (it's only logical to do so, and it's just another 1/2 line of code if you know what I mean).
any tip as to how different they behave under different light sources?

Paper by nature is off-white. White paper is created by bleaching and addition of whiteners which as usually bluish. Paper are also graded according to their closeness to true white. So using plain paper u may get varying degrees of accuracy, but it should suffice as long as its close enough.
I understand about the paper colour accuracy part.. I would think that buying good white paper wouldn't be too taxing, given that the matt surface is ideal for such purposes.. It's alot better on the wallet too.
 

Status
Not open for further replies.
Top Bottom