# 18% grey or white card for white balance setting



## shingfan (Jan 26, 2007)

what is an 18% grey card?....and how white should a white card be?....when setting white balance...which is more convenient to use?......so..when setting the white balance....should i put the paper very close to the camera...or use long focal lenght?....any difference?


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## Digital Matt (Jan 26, 2007)

Either one will work fine.  An 18% grey card is used for determining proper exposure, and for calibrating a meter.  Meters always give recommendations to make your exposure 18% grey, or "middle" grey.  The meter has no idea what your subject matter is.  It's up to you to decide how to expose based on the meter.

As for white balance, all you need is a neutral tone to balance off of.  White balance is a term that comes from video, and somehow has made the transition to digital still photography.  A grey card works just as well as a white card.  You need to have the card illuminated by the same light that is hitting your subject, or chosen scene.  If you are shooting a model, have them hold the card.  If you are setting a custom white balance, depending on your camera, you may have to fill the frame, or it might let you select a spot in the photo to wb from.  I don't know what camera you have.  If you are planning to set the white balance in software later, it doesn't have to fill the frame.  You'll just click on it with an eyedropper to select WB.


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## shingfan (Jan 26, 2007)

so i can grap a piece of regular printing paper and it should do a fine job acting as a white reference?.....does it matter if there has folding line.......or it is not that critical and it doesnt need to be perfectly smooth surface when evenly spread color?....i'm thinking of putting a couple pieces of printing paper in my camera bag to use for setting white balance if this is okay in your opinion...but of course...they are too big to fit in the bag so i'll need to fold them...so when i use them...there will be folding lines...wonder if it matters


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## Digital Matt (Jan 26, 2007)

I wouldn't recommend using a piece of paper, because it's not totally opaque.  You want something opaque, so no other colors show through it.  A piece of white foamcoare or mat board is probably smarter.  Folds and creases don't really matter.  You want something to represent neutral color in your scene.


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## ladyphotog (Jan 26, 2007)

Why not just buy a gray card, you can get one for about 10 bucks.


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## shingfan (Jan 26, 2007)

well....three piece of printing papar stacked is probably opaque enough?........or maybe white cardboard?.....i like to put it in the camera bag and carry along easily.....how about focal length?.....does it matter?......better if the card board is farther or closer to the camera?

well....i'm not sure what a grey card is....i'm a newbie....and if i can get something to do the same job for free at home....i would save the $10...lol....


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## ladyphotog (Jan 26, 2007)

shingfan said:


> well....three piece of printing papar stacked is probably opaque enough?........or maybe white cardboard?.....i like to put it in the camera bag and carry along easily.....how about focal length?.....does it matter?......better if the card board is farther or closer to the camera?
> 
> well....i'm not sure what a grey card is....i'm a newbie....and if i can get something to do the same job for free at home....i would save the $10...lol....



You will use a gray card many times for different situations and you will always have it if you take care of it.

This is a gray card:
http://www.kodak.com/US/en/motion/products/tools/card.shtml


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## Digital Matt (Jan 26, 2007)

Focal length doesn't matter.  The paper has to be clearly visible under the same lighting conditions as your subject.


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## ksmattfish (Jan 26, 2007)

Gray cards are a specific tone.  Unless they also say they are color neutral, they may not be.  The standard Kodak gray card (at least the older one I have), for instance, is not color neutral.

This place sells color neutral gray cards.

http://secure.netsolhost.com/664583...vc?Screen=CTGY&Store_Code=CI&Category_Code=GC


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## shingfan (Jan 26, 2007)

when using this grey card...do i need to also include the white and black area in the exposure?....

how much is it different from just using white paper?


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## ksmattfish (Jan 26, 2007)

shingfan said:


> how much is it different from just using white paper?



You can white balance with anything that is color neutral.  The problem is that the human eye is not very good at determining if something is color neutral or not, so you need to know for sure whether the paper is color neutral.


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## shingfan (Jan 26, 2007)

what is the meaning of color neutral?....


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## Digital Matt (Jan 26, 2007)

shingfan said:


> what is the meaning of color neutral?....



Having no color cast.  Usable as a reference point.  If for instance, you white balance off of a red card, your camera or software will shift the color to make that card neutral, which will in turn shift your white balance to very cyan.  You need something that has no color, which is pure grey, or white.


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## shingfan (Jan 26, 2007)

o...i see.....i understand that with white card...there might be contamination and might introduce a bit of color cast........but black card....it is completly black and doesnt reflect any color cast....why is it not a good idea to use black card?....i'm just trying to understand the physics i hope you dont mind


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## Christie Photo (Jan 26, 2007)

shingfan said:


> what is an 18% grey card?....and how white should a white card be?....when setting white balance...which is more convenient to use?......so..when setting the white balance....should i put the paper very close to the camera...or use long focal lenght?....any difference?



A grey card reflects 18% of the light falling onto it.  The back of a grey card is white.  I always shoot both...  grey side first.  The card should fill the entire image.  After shooting the grey card and setting my exposure, I set the white balance.  I then shoot the white side and double-check my exposure.  I look for a thin line on the histogram, straight up and down, all the way to the right but not going off the graph.  Once I have achieved this, I reset the white balance.

Maybe I'm an obsessive-compulsive type.

Pete


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## Christie Photo (Jan 26, 2007)

shingfan said:


> why is it not a good idea to use black card?....i'm just trying to understand the physics i hope you dont mind




Black means no light reflecting.  So....  no light, no data to read.


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## shingfan (Jan 26, 2007)

Christie Photo said:


> A grey card reflects 18% of the light falling onto it. The back of a grey card is white. I always shoot both... grey side first. The card should fill the entire image. After shooting the grey card and setting my exposure, I set the white balance. I then shoot the white side and double-check my exposure. I look for a thin line on the histogram, straight up and down, all the way to the right but not going off the graph. Once I have achieved this, I reset the white balance.
> 
> Maybe I'm an obsessive-compulsive type.
> 
> Pete


 
i like this method very much....very scientific....as you can see...i'm more of a science guy

what do you mean by resetting the white balance after you already adjust it with the grey card?....what do you reset it to?...this part i dont quite understand...i understand that you use the grey card to set hte white balance and use the white side and histogram to verify....not sure what the reset is for if everything checks fine?


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## Christie Photo (Jan 26, 2007)

One more thought....   light metes tell you how to achieve grey.  That's why we meter a grey card to determine exposure.


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## Christie Photo (Jan 26, 2007)

shingfan said:


> what do you mean by resetting the white balance after you already adjust it with the grey card?....what do you reset it to?...



It's just something I do.  I do everything twice.  It's not the quickest way to live my life, but I HOPE it protects me from SOME of my stupid mistakes.

Pete


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## shingfan (Jan 26, 2007)

o.....you mean you do this sequence twice to make sure things are okay and then you just reset to the previously captured white balance setting ....i see

so i guess a grey card is highly appreciated?.....


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## markc (Jan 26, 2007)

I personally prefer white over grey for balance. I'm sure a light grey works just fine in most situations as long as it's neutral, but the closer to black you get, the less light are are having reflected to work from. If you have a dim exposure you might run into issues.


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