White Balance

[Sloseph]

Morning all

This has been pecking my head for a long time now and I really appreciate an explanation

I always hear people going on about setting your white balance with grey card, I can't for the life of me think what the point in this is

My understanding of white balance is that your camera needs to recognise what white is in your picture, so I don't really get why you would use grey card when there is no grey card in your picture

Im guessing my understanding is probably just way out

What is the benefit of using grey card instead of just having it set to auto white balance?

Cheers

[candidrachel]

The way I understand it is that all light meters are colour blind and try to make everything 18% grey so if you place a grey card in the scene and meter off that you will get a more realistic colour and white balance. Also, the light meter in camera reads reflected light not the light that is actually hitting your subject so it can be tricked hence the white cat sitting in snow will come out grey.

That's my take on it. Might be completely wrong

[RichardTaylor]

Be careful.
Grey cards can be used for two purposes.

(1) Can be used for determining your exposure, as it is a "standard" reflective surface, by metering from it.


(2) White balance.
When it is in a photograph it provides a neutral colour reference (grey). So if they are any colour casts due the shooting environment it will show up when you look at the colours on the grey card (for example a blue cast may show RGB as 50,50,75 when all RGB values should be the same for the card). It makes it very easy to correct white balance when PPing (For example using the white balance sampler in Lightroom).

This may help
Gray card - Wikipedia, the free encyclopedia

[FallsCity]

I have a similar question and just happened to see this recent thread so I thought it might be a good place to ask...

I am basically wondering what the difference is in setting your WB using one of those caps vs. using a gray card. If you have an expo disc or one of the generic WB caps, I understand you would point that at the light source and snap a shot to get an accurate reading. I understand they are partially transparent so it is "looking" at the light.

My confusion comes in because gray cards are not transparent, are they? So, would the setting where you take your shot of the gray card matter -- ie take the picture inside and use that custom WB outside and be accurate?

[kcoppock]

Originally Posted by FallsCity

I have a similar question and just happened to see this recent thread so I thought it might be a good place to ask...

I am basically wondering what the difference is in setting your WB using one of those caps vs. using a gray card. If you have an expo disc or one of the generic WB caps, I understand you would point that at the light source and snap a shot to get an accurate reading. I understand they are partially transparent so it is "looking" at the light.

My confusion comes in because gray cards are not transparent, are they? So, would the setting where you take your shot of the gray card matter -- ie take the picture inside and use that custom WB outside and be accurate?

Ideally, you would take a photo of the gray card in the same lighting conditions as the subject. Then (assuming the gray card is actually neutral gray) you have a point of reference to give Lightroom/PS to know what should be considered a neutral gray. If there is a color cast from the lighting, it will correct the White Balance until the gray card is again neutral.

[FallsCity]

Oh okay..So even though you are filling the frame with a shot of the gray card, it will yield different results if you are outside in the sun versus a dimly lit room.

[kcoppock]

Originally Posted by FallsCity

Oh okay..So even though you are filling the frame with a shot of the gray card, it will yield different results if you are outside in the sun versus a dimly lit room.

Yup, because the color cast on the card is going to be different. You're basically just telling the software "This is neutral gray."

The card is going to look different to the camera in different lighting conditions, though, so that's why you need to shoot it for each lighting condition.

Alternatively (and what I do), shoot RAW and eyeball it.