18% Grey Card: WB or EC?

I prefer to use the term "Color Balance" rather than 'White Bal'. It's a little easier on my brain.

mnealtx wrote in post #5524542
I'm not sure I quite understand what you're asking, but let me try.

There IS a connection between using some sort of aid (be it a white card, gray card, black card, expodisc, etc) and setting a white balance for the scene, obviously.

The CWB function in the camera uses one of those aids IN ORDER TO set a white balance, which is a setting to remove any sort of color cast due to the available light. For that reason, whatever aid you use HAS to be color neutral (B=G=R), or it will INTRODUCE a color cast.

Any other WB setting in the camera (AWB, Sunny, Tungsten, etc) is the Canon programmer's 'best guess' as to what a 'proper' WB should be for various scene lighting.

Clear as mud?

OK, since this thread continues (OP, I didn't mean to hijack this!), let me give you a scenario: I go into a Hall, they have the aweful flourescent overheads, I want to set a CWB ... Can I shoot an image of either White/Grey/Black and use THAT image for my CWB?

My second option would be just to snap a picture of ANY of those colors and use it as my "eyedropper" in PP ....

Thoughts?

Cody21 wrote in post #5524702
OK, since this thread continues (OP, I didn't mean to hijack this!), let me give you a scenario: I go into a Hall, they have the aweful flourescent overheads, I want to set a CWB ... Can I shoot an image of either White/Grey/Black and use THAT image for my CWB?

Yup. That's exactly how I'd do it (make sure it's filling the frame...) You're telling your camera that this is "Neutral."

Advantage here is that you don't have to fill the frame, just get it big enough that you can sample it cleanly without any interference from anti aliasing around the edges.

One good reason to use a grey card to use for a custom white balance in-camera is it's easy to expose for - point and shoot. Using a white card it's easy to overexpose, which doesn't do you any good. But as mentioned above, as long as the R/G/B values are equal, any color will do. So an 18% grey card is quite handy for this.

This thread was bugging my so I had to run a quick test.

It turns out that the gray card DOES work for adjusting white balance.

All pictures were taken under a 5 halogen bulb lamp (tungsten)

1. AWB, no PP

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Gray Card…White Paper. What’s best?

mnealtx wrote in post #5523898
The Whibal cards have the white and black stickers on them so that they can be used to quickly set white and black points in post processing. The gray card can be used to not only set a custom WB but also to set base exposure.

Discovery - gray card and WB absolutely DO mix.

The camera doesn't care WHAT 'color' the card is... only that it is BALANCED (ie, Red=Blue=Green). You can use anything from pure white (255,255,255) to pure black (0,0,0) and anything in between... as long as the colors are balanced.

And, you might want to add, not clipped (specifically referring to the white and black parts). If the white or black is clipped, WB will be thrown off.

PacAce wrote in post #5528616
And, you might want to add, not clipped (specifically referring to the white and black parts). If the white or black is clipped, WB will be thrown off.

Can you explain what 'clipped' white/black is?

As stated any neutral gray will work. you can find a lot of different ones, 18% is just traditional. Believe it or not 18% is half way from white to black. That's why it was used with film.

White cards are also used in video to set zero point. However white is not allways white. Thats why the gray is more accurate. I used to be a car painter. And I can tell you there are about 50 'pure' whites on cars. If you pick the wrong one you can see it. Same with the cards. IF you get different brands and put them together. you will see the ballence if off. But 18% gray.... or any "calibrated" color. You know what you are getting.

White is the most important to me. First, do you understand how the histogram works?
FAQ's on HISTOGRAM

Curtis N found that a blown red channel is a problem:
How NOT to expose to the right
How to fix it:
Restore Those Clipped Channels

Discov3ry wrote in post #5528853
Can you explain what 'clipped' white/black is?

Clipping is the point where you lose detail in the selected color. Think over exposed/under exposed.

Discov3ry wrote in post #5528853
Can you explain what 'clipped' white/black is?

Clipping occurs when an area is overexposed to the point where it registers as white even though the original color may not be truly white. Or when an area is underexposed to the point where it registers as black even though it really isn't.

So, if you're using a white card and it is overexposed, that card is going to show you white because it got clipped even if there was originally a color cast on it from the light source. This clipped area can not be used reliably for WB correction.

for Discov3ry --- nice sample pics. So, which of those do you consider the most accurate to what you are seeing on the table????

Cody21 wrote in post #5529517
for Discov3ry --- nice sample pics. So, which of those do you consider the most accurate to what you are seeing on the table????

#4 comes the closest followed by #6

#4 - pp'ed in DPP by using the pick tool to select 'custom white balance' by clicking on the gray card.
#6 - custom white balance by using the in camera 'custom balance' set with a picture of the gray card (#5)

Now, some questions:
-when taking a picture of the gray card (or white card) should the in camera WB be set to AWB or manual corresponding to the ambient light source? If you look at #5 it doesn't really look gray compared to #4 (which I think is the closest to reality). If that picture it used to custom balance the camera then it may produce unbalanced results. Hence, the last picture (#6) which is balanced in camera does look balanced yet still not the same as #4

-the gray card I used is a professional grade from a respected photo store. Yet when you look at it in #5 you can see a lot of shadows and reflections. Can this have a negative impact while post-processing and using the pick tool to select control pixels?

It doesn't matter what WB you use for that.

Not to me. I don't know what's happening in there, but it's not a good Custom WB.

Shouldn't hurt. If it bothers you, shoot it out of focus.