Understanding 20D white balance ?!?!?

[DavoMrMac]

Sorry for all these questions guys.

I read the manual and set the Custom White Balance on my 20D, so I guessed this would mean when I took the shot of my white sheet of paper it would come out 'white', but it came out grey.

What am I doing wrong?

[roanjohn]

First manual focus and shoot a blank white paper in the room.

Press MENU and go under CUSTOM WB. Toggle between shots to select the photo with the white paper. PRESS "SET"!!! This will enable the camera to remove the color cast. Don't forget to choose CUSTOM WB on your WB.

Take another photo and VIOLA, your paper is now white!!!

Ro1

[kawter2]

White balance, balances the color casts so that when you properly expose something that is white it will appear white, instead of bluish or orangeish.

Your problem is that you aren’t properly exposing the white sheet of paper, WB settings have nothing to do with how dark or light a given exposure is

[goldstrikn]

I am a newbee, so how does the Grey Card work? Do you hold it to your subject or you preshoot it and save it?

[DavoMrMac]

roanjohn - thanks for the response, that is exactly what I do, but when I then re-take the same piece of paper it is grey.

hmmmmm

[kawter2]

most people use grey cards for exposure (although you can use them for WB as well)

For exposure, your light meter exposes a subject by averaging the brightness values of a exposure point to be the same value as an 18% grey. If you meter a grey card you are assured that because the camera is trying to make everything that luminance, you will meter correctly.

You can use the grey card for WB in the exact same manner you would a white sheet of paper, your WB subject does not have to be “white”, just as long as it is color neutral/balanced



here is the result of a Google search
http://home.nc.rr.com/tspadaro/The_Grey_Card.html

[kawter2]

roanjohn - thanks for the response, that is exactly what I do, but when I then re-take the same piece of paper it is grey.

hmmmmm


Please read my 1st post

[mbze430]

I am a newbee, so how does the Grey Card work? Do you hold it to your subject or you preshoot it and save it?

Place the grey card at the subject's area than reflect it against the primary light source. Take the picture of that grey card. Than use the Custom WB option, and choose the picture you just took of the grey card.

[roanjohn]

roanjohn - thanks for the response, that is exactly what I do, but when I then re-take the same piece of paper it is grey.

hmmmmm

........first, check that you have CUSTOM WB on your INFO LCD.

If it still appears grey.......adjust your exposure........the camera will automatically underexpose a white scene to make it neutral (GREY)....so adjust your exposure to about +1.

Remember: when shooting bright objets (snow, beach).....+1
when shooting dark objects (tuxedo, black dog) -1.

Ro1

[mbze430]

roanjohn - thanks for the response, that is exactly what I do, but when I then re-take the same piece of paper it is grey.

hmmmmm

That's because the metering system is doing exactly what it is program to do. Make everything 18% Grey. a white piece of paper will turn grey. You need to add +1 or more Exposure Value to make the paper look white

[DavoMrMac]

Thanking you.

[dhbailey]

That's because the metering system is doing exactly what it is program to do. Make everything 18% Grey. a white piece of paper will turn grey. You need to add +1 or more Exposure Value to make the paper look white

When I set the custom white balance, the next shot has white things come out white with no need to set the exposure value to anything different.

[kawter2]

When I set the custom white balance, the next shot has white things come out white with no need to set the exposure value to anything different.

OMG.... **shoots self in head**

[DavoMrMac]

hmmm, now I am confused, no definitive answer.

Help !

[kawter2]

hmmm, now I am confused, no definitive answer.

Help !


OK let me see if i can clairify. when you meter the camera takes EVERYTHING in the giving METERING ZONE and exposes so that it is 18% grey. If the only thing in your metering zone is a white piece of paper.. guess what..... it will come out grey. Because dhbailey is meetering the entire scene and the camera is averaging everything in the scen to create a corect exposure, because his exposure is correct, the whites come out white.


As it relates to WB, (stated above) WB has no relation to how bright or dark your whites are, it only adjusts the colorcasts so they don't have funky tints to them

[robertwgross]

The basic and fundamental problem here is that you MUST separate white balance from exposure. Those are two rather different things, and you must not blur them together.

White balance is whether the pure white dress looks pure white, or whether it looks a little yellow or a little pink.

Exposure is whether the white dress looks pure white, or whether it looks gray. This could just as easily be in B&W.

Two completely different things.

---Bob Gross---

[DavoMrMac]

So let me get this one final time.

If I white balance using a white sheet of paper, then take a shot using custom white balance, correctly exposed, the following will happen.

1. Shot of white piece of paper will come out grey.
2. Shot of a scene, with the white piece of paper in it, the white will come out white.

Is this correct?

Secondly, why do some use grey card to set white balance?

[Phil V]

So let me get this one final time.

If I white balance using a white sheet of paper, then take a shot using custom white balance, correctly exposed, the following will happen.

1. Shot of white piece of paper will come out grey.
2. Shot of a scene, with the white piece of paper in it, the white will come out white.

Is this correct? YES Provided the scene is metered correctly.:!:

Secondly, why do some use grey card to set white balance?. If it's a pure neutral grey card it can be used. However it's far easier for our eyes to tell a pure white than a pure grey, that's why a white piece of paper is easy. The card I have for WB setting is white grey and black. This means it exposes correctly too (the black cancels out the white for an overall grey) :)

[robertwgross]

When you are setting a Custom White Balance, it is important to use a card without any color tint, like pink or blue or yellow. You can do that with a pure white card, or you can do it with a pure gray card. Pure, though.

A completely different subject is exposure. If you shoot a fully automatic camera at a white card, it will likely turn out an image that is about 18% gray. Surprise! That is what it is supposed to do. An automatic metering system has to make the assumption that everything averages out to 18% gray, so it gets the exposure to produce that. I'm taking a wild guess that you didn't really want a pure white dress to look like 18% gray. So, that is what exposure compensation is all about. The human operator is smarter than the camera's automatic metering system. The operator says "Hmmm, I getter adjust EC to be about +1.0 on this one. Maybe +1.5." VOILA! The pure white dress looks pure white.

---Bob Gross---

[DavoMrMac]

Thanks for all your help.

[Jon]

And the reason some of us use (and Canon suggests) using a grey, rather than a white, card is that a white card, if you also expose correctly, may blow out one of the colour channels, so your white balance would be thrown off. The CWB computer sees the central area, and applies compensation so that the R=B=G. That assumes that R, B, and G are all within the recordable levels for the sensor. If you had a strong blue (or UV) that blew out, burt the red and green were both (even if only just) within capturable range, the B value would be falsely low (couldn't record the true B - it blew out, remember?), and you'd get a bad CWB.