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Author Topic: How to use a Grey Card  (Read 5708 times)

Offline donoreo

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How to use a Grey Card
« on: February 18, 2014, 11:53:34 AM »
This is a tutorial I wrote for my camera club's newsletter. 

A grey card can be used to do two things:

1. Set a white balance
2. Set proper exposure

First, what is a grey card?   To state the obvious, it is a card, fold up reflector or even a sheet of paper that is the colour grey.   Wikipedia has this to say:

A grey card is a flat object of a neutral grey colour that derives from a flat reflectance spectrum. A typical example is the Kodak R-27 set, which contains two 8x10" cards and one 4x5" card which have 18% reflectance across the visible spectrum, and a white reverse side which has 90% reflectance. Note that flat spectral reflectance is a stronger condition than simply appearing neutral; this flatness ensures that the card appears neutral under any illuminant.


Sounds very technical.  The important parts of that statement are the 18% and flatness.   In other word it is a flat (non-reflective) grey card. 
Set a White Balance

There are two ways of doing this.  You can set a custom white balance in the camera or you can use a reference photo to set the white balance in your editing software.  Setting the white balance in the camera is the easiest because once you do it you are done for all photos until you change the white balance to another setting or the lighting conditions change.   This method also appeals to those who like to get it right “in camera” and prefer to as little post processing as possible.

Setting White Balance in Your Camera

The details on how to do this will vary slightly by brand of camera and even model of camera in some cases.   The basics all remain the same but consult your camera’s manual for details.

1. Take a photograph of the grey card near to the subject you are photographing.   Make sure the grey card is getting the same light as the subject.  If a portrait it is common to have model hold the card in front of their face.  Try to fill the frame with as much of the card as possible.  This helps the camera’s metering system. 
2. Select the custom white balance on your camera (Canon often has a button on the right of the LCD, Nikon has the same on the left or can be a menu option on these and other cameras).   Your camera will ask for a photograph to use setting the white balance.  Select the image you took of the grey card. 
3. Before taking another photograph, access the white balance settings on your camera and select the custom one.  This will use the white balance set in the previous set. 
4. Repeat the steps as lighting conditions change.  Custom really means custom to the light conditions as you set them in the first photo.   If the light moves or you move, change the white balance!

The last step is an important one, especially if you shoot jepgs.  You must reset or change the white balance when the lighting conditions change.  If you are shooting the same thing for several hours outside, the sun is going change position and change your lighting.  If you move to a different location, you need to change the white balance again to match the lighting conditions there.   

If you forget all is not lost because you can fix an incorrect white balance in your editing software, but that defeats the purpose of setting it in the first place.   The warning for jpegs is because the white balance is harder to correct after in your editing software than it is for raw photos.   It can still be done as long as the white balance is not too far off.   

Setting the White Balance in your Editing Software

The way to do this in your editing software varies of course.   I will cover Photoshop, Photoshop Elements and Lightroom. 

Photoshop and Photoshop Elements

Photoshop uses Bridge and Elements uses the Organizer to catalogue your photographs.  Open whichever you have and we will start from there. 

1. Select the photograph with the grey card plus any others that are lit under the same lighting conditions.   
2. Open all of these images into Adobe Camera Raw (if jpegs you can still do this be using the File Menu and Select “Open in Camera Raw” or Open As Raw, the actual menu option varies depending on your version of the software).
3. In ACR select the photo with the grey card in it.  This photo should be visible in the main window.
4. Select all the other images by clicking the Select All button.
5. Select the White Balance tool (the eye dropper) icon from the menu bar.
6. Having the eyedropper tool selected, click on the grey card.
7. If they are raw files, continue on with any other adjustments you need to make in ACR.  You can also make adjustments to jpegs in ACR as well. 
8. Select Done to save the images or Open Images to do further editing in Photoshop or Elements.

This will have set the white balance for all of the selected photos.   

Lightroom

In Lightroom the process is slightly different.  We will start after you have imported the photos. 

1. Open the photo with the grey card in the development module.
2. Select the White Balance tool (the eye dropper) from the Basic panel.
3. Click the eyedropper on the grey card in the photo.  The white balance is now set. 
4. Select all of the other photos that are lit with the same lighting conditions. 
5. Select the Sync button at the bottom of the right hand series of panels.
6. Uncheck all of the boxes except the White Balance check box.
7. Click on the Synchronize button to apply the custom white balance on all of the selected photos.

Using a Grey Card to Set Proper Exposure

Grey cards, for being so simple, are a multi-purpose tool.  Not only can you use it to set a proper white balance but you can use it to set a proper exposure as well.   Often very bright scenes, such as snow, can fool the meter in the camera to underexpose.  The opposite can also happen with a very dark scene leading to over exposure.   A grey card can fix both. 

1. Select a centre weighted or spot-metering mode on your camera (the name of this may vary from Canon to Nikon to Sony, etc). 
2. Fill the frame with the grey card.
3. If using full manual mode you can adjust your aperture and shutter speed to get the correct exposure from the grey card. 

Or

3.  If, like most, you are using a semi-auto mode like Av (A) (aperture priority) or Tv (S) (time value or shutter priority) you use the exposure lock (usually a button marked with * ) on your camera when you point at the grey card.  Check your camera’s manual for full details for your camera. 

If you are using manual mode of your camera you can recompose and take your photo.  However, if you are using Av or Tv you will probably need to keep holding the Exposure Lock button while you recompose and take your photo. 
 



Offline SimonW

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Re: How to use a Grey Card
« Reply #1 on: February 18, 2014, 12:19:28 PM »
A very comprehensive and useful posting. I appreciate the work it took. Thank you.
Simon Warren
(in Dunning, Scotland)

Offline donoreo

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Re: How to use a Grey Card
« Reply #2 on: February 18, 2014, 02:24:08 PM »
You are welcome.  I thought I would share. 

Offline Mick

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Re: How to use a Grey Card
« Reply #3 on: February 18, 2014, 09:09:40 PM »
Nice one Don, thanks for that handy info.  Would make a great article you know.  ;) http://cameracraniums.com/forum/index.php?page=articles
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Offline donoreo

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Re: How to use a Grey Card
« Reply #4 on: February 19, 2014, 12:48:24 AM »
How do I do that?

Offline StephenBatey

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Re: How to use a Grey Card
« Reply #5 on: February 19, 2014, 08:54:59 AM »
As a black and white photographer, I can't comment on the white balancing part. On the exposure, at the risk of stating the obvious, the card should be placed in the same lighting conditions as the subject. Additionally, unless Kodak have changed their recommendations, the card should be placed at a 45 degree angle to the illumination. This is because most (possibly all) meters are actually calibrated to a 12% reflectance, not 18%; and the change of angle reduces the reflectance.

I don't know if camera makers tell you what their meters are calibrated to; but in the case of at least some hand held meters the makers do release enough technical information for you to be able to calculate the value.

From memory, you can find details of how to calculate in "Way Beyond Monochrome", although it may just possibly be in Ctein's "Post Exposure". One of the two, anyway. But I suspect if you have a built in meter, the info may not be available.

Offline ABERS

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Re: How to use a Grey Card
« Reply #6 on: February 19, 2014, 09:23:00 AM »
Just as an aside, in 30+ years I've never seen anyone use a grey card, even though for many years one nestled in the bottom of my camera bag.

When out and about they are totally impracticable, in a studio and still life situation O.K.

If you must impose all sorts of manual tasks on yourself to produce a decently exposed image, and enjoy the intricacies of such imposition, all well and good.

However taking a reading from the back of your hand at arms length always worked for me when working with film in an open air and rapidly changing light source situation. That's when I worked with everything on 'manual'. 8)

That's all gone now, I just correct my faults in L/room. ::)

Offline Andrew

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Re: How to use a Grey Card
« Reply #7 on: February 19, 2014, 12:03:35 PM »
I can comfortably say there is one type of photography where a grey card is essential - under water photography using digitial cameras.

Given the way water affects the available light and colours at differing depths - it becomes very useful to set a custom white balance instead of adding bundles of filters, not least of which the grey card can also double up as a writing slate on the back side and easily fits in the pocket of a BCD (the part that makes you float or sink).

Since converting to, and committing to shooting in raw, I very much leave WB in auto and correct it all in LR5.

That is not to say that your work has been in vein - I know people who like to take their knowledge to the very basics of understanding an aspect of photography and such an article would be most welcome.
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Offline donoreo

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Re: How to use a Grey Card
« Reply #8 on: February 19, 2014, 01:26:34 PM »
It was written because of a request of a club member.  There were many people on our snow outing that had problems with white balance and exposure.  Lots of blue or grey snow in the photos.   

Offline Andrew

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Re: How to use a Grey Card
« Reply #9 on: February 19, 2014, 03:43:09 PM »
It was written because of a request of a club member.  There were many people on our snow outing that had problems with white balance and exposure.  Lots of blue or grey snow in the photos.

Exactly - very useful to a whole bunch of people   :-[

Just not me and Abers  :doh: That's the trouble with 'old farts' - you can forget why something was useful when you've worked so logn without it
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Offline donoreo

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Re: How to use a Grey Card
« Reply #10 on: February 19, 2014, 06:45:50 PM »
My camera club has plenty of old farts :)  The same questions get asked over and over because their hearing is going and they do not hear the questions!  In fact just last week we had one member (husband of the most recent past President) pass away.  Like many camera clubs our average age is "retired". 

Offline StephenBatey

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Re: How to use a Grey Card
« Reply #11 on: February 19, 2014, 08:07:01 PM »

However taking a reading from the back of your hand at arms length always worked for me when working with film in an open air and rapidly changing light source situation.

I used to have problems with metering until I read a piece of advice from Victor Blackman in AP about 50 years ago. The advice was to meter from the palm of your hand and increase the exposure by one stop. The palm, not the back, he advised because palms don't tan as the backs of hands do. There is apparently a great degree of uniformity in the Caucasian palms of hands.

This is of course basically an incident light reading - as a grey card is.

Offline Mick

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Re: How to use a Grey Card
« Reply #12 on: February 19, 2014, 08:22:35 PM »

How do I do that?


Don, down the right hand side of the home page you should see a user panel, similar to this, although you won't have quite so many options in it, you should see the write article links.  You should be able to embed images if necessary, but you'll need to upload them somewhere.  The article system is available to all members of CC, should anyone wish to write one (some). 

If any of you guys want to add images for articles then I can give access to the test site, where there's another gallery running, and embed them from there.
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Offline donoreo

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Re: How to use a Grey Card
« Reply #13 on: February 19, 2014, 09:07:05 PM »
There are no screen shots, my word paint a picture  :uglystupid2:  I think I have it created now. 

Offline Mick

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Re: How to use a Grey Card
« Reply #14 on: February 19, 2014, 09:27:03 PM »
There are no screen shots, my word paint a picture  :uglystupid2:  I think I have it created now.

Found it and approved it. Thanks for writing that, I'm sure some will find it very handy.  :tup: 

I have turned off the side panels when viewing your article.  As you'll also notice any article created by the members is also added automatically to the Article index.

Feel free to add more if you wish.  Same goes for anyone else who gets the urge.  ;)
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