Gray Card


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Dec 5, 2007
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#1
Hi,

Need help on the 2 sentences below, read and read ....
still catch no ball...

1. All in-camera meters are designed to measure an average reflectance of 18 percent gray.
So ??
2. A gray card can be used to accurately adjust the tones in shots using picture editing
software.
How ??
 

Dec 2, 2006
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#2
snap the picture of the 18% gray at the location where you want to take the photo.

Use DPP white balance picker on the 18% gray photo and save it as one of the setting (the 123).
Use the setting on the subsequent pics that you take at the same location under the same lighting.
 

Dec 2, 2006
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#3
Another way is use your in camera function of custom white balance. Then go to custom function and at set white mabalance use the picture of the gray card as the sample.
 

Dec 5, 2007
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#4
huh ?? how i know is 18%

*faints*

Meaning, outdoor, i half clutch on a gray card.. (camera will suggest an exposure)
then i change focus to the subject that i wan. right ?
 

catchlights

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Sep 27, 2004
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#5
Hi,

Need help on the 2 sentences below, read and read ....
still catch no ball...

1. All in-camera meters are designed to measure an average reflectance of 18 percent gray.
So ??
2. A gray card can be used to accurately adjust the tones in shots using picture editing
software.
How ??
#1, So.. if you meter a black object and shoot it what meter tells you (fill out the frame), the black object will be overexposed and turn into gray
and
if you meter a white object and shoot it what meter tells you (fill out the frame), the white object will be underexposed and turn into gray

finally, if you place the gray card beside the whatever object, and take the meter reading from the gray card, remove the gray card and expose the scene accordingly, the object will be correct exposed, regardless what tone is of the object.

#2, if you shoot a gray card place beside the object, but didn't adjust the proper white balance, you can use the gray eye droplet tool in curve adjustment or level adjustment. click on the gray card in the image, it will adjust the color tone into neutral tone.
 

catchlights

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Sep 27, 2004
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#6
huh ?? how i know is 18%

*faints*

Meaning, outdoor, i half clutch on a gray card.. (camera will suggest an exposure)
then i change focus to the subject that i wan. right ?
if the card is claim to be a 18% gray card, it will be a 18% gray.

to use it, fill the frame (or metering area if you use spot metering) with the gray card under the same lighting as your subject, adjust your exposure indicator till it show middle (correct exposure). remove gray card, compose and focus your subject, shoot it the exposure setting you obtain with the gray card.
 

codered

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Aug 12, 2006
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#7
Not sure if i should start a new thread...

Had difficulty to find gray card in Singapore. Looking for the card only - not those collapsible type. Any idea?
 

aryanto

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Feb 16, 2005
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#10
use expodisc and custome while balance feature (only available in some camera) :)

but the downside it is expensive (expodisc)
 

Octarine

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#11
use expodisc and custome while balance feature (only available in some camera) :)
but the downside it is expensive (expodisc)
There are DIY solutions as well (pringles cap, white foam cup etc). Custom WB is standard in all decent cameras. Even PnS have it, although sometimes deeply hidden in the settings menu.
 

simranjits

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Apr 11, 2008
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#14
Why not use your palm and compensate for exposure by 1 stop? Your palm reflects roughly 35-36%, so going up one stop is like using a gray 18% card!
 

Octarine

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#15
how to do? those are not grey color rite?
No, they are not gray but the basic principle is the same, regardless whether you use gray card or Expodisk. The camera needs to know the 'offset' from 18% gray / neutral white.
Simple example: sunset. The light coming in is not white but very warm = more red. So if you want to remove this excessive red portion you need to set the WB accordingly: If you use a gray card then the sunset light reflected from the gray card will contain more red. The camera compares this against 18% gray stored in internal memory and gets the 'offset'. Which means: the offset needs to be subtracted from the image to get neutral white.
The same happens when using Expodisk or pringles cap: you put the cap or disk in front of the lens. The white cap will diffuse all incoming light evenly (kind of white/gray fog) and the camera can determine the offset to neutral white.
The details of setting the WB in the cam depend on brand and model. AFAIK there are two major ways: either you shoot a picture (of gray card or through the Expodisk / cap) and use this for "Custom WB" or you point the camera towards the object and get the reading immediately. Please check your camera manual for that.
In addition, there are two ways to capture the light for WB when using Expodisk / pringles cap: either directly into the light source or pointing towards the object. What you do depends on how you want to set the WB. Either you want to neutralize colour cast by the light source or you want to get the object neutral, regardless of surrounding light.
 

catchlights

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#18
Hmmm, can we DIY our own grey card? Like print out from software like photoshops...
you can make a grey card in Photoshop, it is very simple, just make a doc with RGB value of 128, 128, 128 with do.

but how accurate will the print out be? whether is injet print, photographic print or whatever, it couldn't be certain unless you have a device to test it truely neuture and is at mid tone.
 

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