set white balance with a grey card?

Hi all

Although I am a beginner, I think I have a basic understanding about the
need to have white balance set to suit the prevailing light when taking
pics with my 60D.

However, i bought a pretty helpful book on the Canon 60D that included a
grey card to use to set white balance ???

Yep, a GREY card to set WHITE balance!!!

Obviously this must be right, but the book doesn't explain how setting
the grey balance is the same as setting the white balance, and I have
not (so far) read anything about setting the grey balance in anything I
have read.

So I am mystified - can anyone explain this?

Thanks in advance

David

On 2011-05-11 19:36:03 -0700, David Ross said:

Hi all

Although I am a beginner, I think I have a basic understanding about the
need to have white balance set to suit the prevailing light when taking
pics with my 60D.

However, i bought a pretty helpful book on the Canon 60D that included a
grey card to use to set white balance ???

Yep, a GREY card to set WHITE balance!!!

Obviously this must be right, but the book doesn't explain how setting
the grey balance is the same as setting the white balance, and I have
not (so far) read anything about setting the grey balance in anything I
have read.

So I am mystified - can anyone explain this?

Thanks in advance

David

Yes, you use a Grey card to set white balance. You are not setting the
"grey balance".

Depending on the photo-editing software you are using you should have a
custom "white balance" tool, along with the usual list of standard
settings.

The idea is to have a neutral grey card placed in your scene, under the
lighting you will be shooting in. This reference shot can be taken at
the beginning of the set on images, or at the end.
I use a WhiBal reference card.
http://mtapesdesign.com/whibal/
Take a look at their user guide PDF, and video tutorials.
http://www.whibalhost.com/_pf_sitefi...rGuide_V10.pdf
http://www.whibalhost.com/_Tutorials/WhiBal/01/


--
Regards,

Savageduck

On Thu, 12 May 2011 12:36:03 +1000, David Ross
wrote:

Hi all

Although I am a beginner, I think I have a basic understanding about the
need to have white balance set to suit the prevailing light when taking
pics with my 60D.

However, i bought a pretty helpful book on the Canon 60D that included a
grey card to use to set white balance ???

Yep, a GREY card to set WHITE balance!!!

Obviously this must be right, but the book doesn't explain how setting
the grey balance is the same as setting the white balance, and I have
not (so far) read anything about setting the grey balance in anything I
have read.

So I am mystified - can anyone explain this?

Thanks in advance


Yep, in simple terms the camera needs to be told that what it saw was
something that reflected Red Green and Blue in equal proportions. It
doesn't specifically matter what the colour of that object is though
logically it is going to be something grey or off-white. Some whites
will reflect blues more strongly causing the white balance to be off.


--
AnthonyL

David Ross wrote:
Yep, a GREY card to set WHITE balance!!!

Obviously this must be right, but the book doesn't explain how setting
the grey balance is the same as setting the white balance, and I have
not (so far) read anything about setting the grey balance in anything I
have read.

So I am mystified - can anyone explain this?

What's the difference between a grey object and a white
object? *None!*

Same object, but it will show up as grey or white
depending on the amount of light and the context. If
other objects close to it are illuminated with the same
amount of light, it will be grey. But if all nearby
objects have 1/64th as much light, the "grey" object
will be white. And likewise, if that "grey" object has
1/1000th as much light on it as do nearby
objects... you'll see it as black!

What is needed to calibrate color balance, which is
perhaps incorrectly called "white balance", is an object
that reflects red, green and blue equally... and
sufficiently to provide an accurate measurement.
Generally any object that has a reflectance of more than
perhaps 5 to 10 percent (a grey card is 18 percent) will
work. And that includes a "white card" with 90 percent
reflectivity.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

On Thu, 12 May 2011 19:30:39 +0200, Alfred Molon
wrote:

In article , David Ross
says...
However, i bought a pretty helpful book on the Canon 60D that included a
grey card to use to set white balance ???

I've used grey cards in a number of cases to get accurate colours:
http://www.molon.de/suche/?s=grey%20AND%20card

I've just started experimenting with the SpyderCube
http://spyder.datacolor.com/product-cb-spydercube.php
It enables me to make full use of NX2's one-click ability to set
black, white and grey points respectively. It's too early for me to
have reached any conclusions about it.

Regards,

Eric Stevens

7On Thu, 12 May 2011 07:54:16 -0700 (PDT), David Dyer-Bennet
wrote:

On Wednesday, May 11, 2011 9:36:03 PM UTC-5, David Ross wrote:
Hi all

Although I am a beginner, I think I have a basic understanding about the
need to have white balance set to suit the prevailing light when taking
pics with my 60D.

However, i bought a pretty helpful book on the Canon 60D that included a
grey card to use to set white balance ???

Yep, a GREY card to set WHITE balance!!!

Obviously this must be right, but the book doesn't explain how setting
the grey balance is the same as setting the white balance, and I have
not (so far) read anything about setting the grey balance in anything I
have read.

So I am mystified - can anyone explain this?

Any "neutral" color card will work; you have to expose it properly.

What's needed is an exposure where all three color channels have
data -- no channel is "clipped" (off the top or bottom). White balance
is all about the relative exposure of the three channels.

So, white will work, grey will work. So long as they're precisely
neutral tones. Black would work, if the light was bright enough. They
all come out grey with suitable exposure.

I'm not sure why they prefer grey to white (the choice of card
with that book). If you fill the frame with the card, the AE system
will expose them all the same, so it doesn't matter. If you put the
card as one small item in the frame, though, a white card is more likely
to be exposed so at least one channel clips, whereas a grey card is
less likely; that could be the reason. Or maybe they want to use the
same card for other uses, like local exposure measurements; grey is
the standard for that.

I use the Tapes Whi-Bal card by setting it in the scene before my
series of shots, and then using the card in the image to set my
white/neutral/black points in Photoshop. Works a treat.



--
Tony Cooper - Orlando, Florida

AnthonyL wrote:

Some whites
will reflect blues more strongly causing the white balance to be off.

Often a problem with white paper. Worst are those whiteners
(often in cheap paper) that take UV light and return it as blue.
Due to the way our eyes work, bluer is often seen as white(r)
because a neutral white will be yellowish in comparison.

-Wolfgang

On 2011-05-17 08:54:36 -0700, Wolfgang Weisselberg
said:

AnthonyL wrote:

Some whites
will reflect blues more strongly causing the white balance to be off.

Often a problem with white paper. Worst are those whiteners
(often in cheap paper) that take UV light and return it as blue.
Due to the way our eyes work, bluer is often seen as white(r)
because a neutral white will be yellowish in comparison.

-Wolfgang

Hence the need for a spectrophotometer calibrated, neutral grey card
for establishing an accurate WB.

....and not all grey cards are equal. Just because they have told you it
is an 18% grey doesn't meant that it actually is. However for the most
part any grey card at approximately 18% is going to give you more
accurate results than a white target, which as you have stated, can
leave you with a color cast.
Using a white target for WB can also lead to very blown highlights.

A clean white card target is useful for setting a "white" point, not a
"white balance." those are two different things.
The same goes for setting a "black" point using a "true black" target.

--
Regards,

Savageduck