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DPChallenge Forums >> Hardware and Software >> PRE White balance on D70 - use gray or white?
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 07/13/2005 09:06:59 PM · #1
I'm not sure I understand how this is supposed to work. The manual says that you can use a gray card or a white one for preset balance, but how does the camera know whether it's gray or white?
I'm used to using a white card, and it seems to work, but would gray be better?
 07/13/2005 09:11:48 PM · #2
if this is to set a custom white balance...you need a white card, if this is to have a reference photo of the "grey" point for image editing then, as the name says, a grey card (but sine you'd be doing a grey...you should also have a white and a black)
 07/13/2005 09:16:04 PM · #3
I have yet to set it on my d70, but I've seen a friend do it. He used a white card. If it's anything like the rebel, just shoot a white piece of paper in the environment you are going to be working. Select the photo and the camera will import the data off of it.
 07/13/2005 09:19:49 PM · #4
Originally posted by Gil P:
if this is to set a custom white balance...you need a white card, if this is to have a reference photo of the "grey" point for image editing then, as the name says, a grey card (but sine you'd be doing a grey...you should also have a white and a black)


Helps with eyedropper tool for levels, curves, etc;I assume.
 07/13/2005 10:51:02 PM · #5
Excuse the contrived example, but I quickly shot a couple of pictures with my daughter's doll against a white wall just to illustrate this:

White balance is set to:
Sunny Auto white balance

As you can see, the auto white balance picture comes closer to reality than one where the white balance is set to sunny. (I know ... duh ... but hang on a second)

Next I shot a picture of the white wall, here:



I used the above image to set my white balance. Basically, in the camera, I select the "set white balance" option. It told me to pick an image that was primarly white. I selected the above image. Then it told me to set my white balance setting to "custom" (in order to begin using the above image as my white balancer).

Then I reshot the same image one more time and now I got this:



Okay, so what's really going on?

If I go to the image that was auto-white-balanced and put my dropper up in the top left blank area, I get a reading of:

C: 8%
M: 25%
Y: 44%

This is telling me there is a yellow cast within that area of the picture. If I click inside of my "white wall" picture (the one used for white balancing) I get these readings:

C: 38%
M: 53%
Y: 80%

Again showing a heavy bias towards yellow. If it were white, all three values would be equal. So, what about my final picture, with the custom white balance? Here I get these values:

C: 22%
M: 18%
Y: 17%

Darn near equal values (and they fluxuate a bit as I move the dropper around) The point is... the white balance worked by subtracting out the yellow and magenta until all three values were nearly the same.

And that's what setting a custom white balance will do for you. And you can also see that this method is superior to auto-white balance which came close ... but still missed the mark.
 07/13/2005 11:09:53 PM · #6
Good samples, great write-up. That should be a tutorial.
 07/14/2005 01:35:44 AM · #7
I've seen peopel recommend both. Perhaps you should try both and let us know. If it was me, I'd use white. Since I shoot in RAW, I adjust with the in Rawshooter Essentials if I think it's off and hence don't use any cards at all.
 07/14/2005 03:27:38 AM · #8
Originally posted by WhidbeyPix:
I'm not sure I understand how this is supposed to work. The manual says that you can use a gray card or a white one for preset balance, but how does the camera know whether it's gray or white?
I'm used to using a white card, and it seems to work, but would gray be better?


You can use either. The point is to use a card where red green and blue are equally represented, which makes a shade of gray.

A white card might give more accurate results, especially in low light conditions.
 07/14/2005 09:27:52 AM · #9
I agree with willem, a gray or white card will work the same. I saw one recommendation to "just shoot a white piece of paper." Be careful here, some papers are "whiter than white" because they respond to UV. Camera sensors see color differently than we do, and you might not get a poper white balance shooting paper with UV whiteness enhancers.
The best way is to use a card that is designed to give neutral results and to be stable over time.
07/14/2005 09:36:29 AM · #10
If I understand it correctly, the camera adjust whatever you point it at to try and make it a neutral white (actually it's like 15% gray). So either will work. For some cool effects point the camera at something red and do a custom white balance.

I carry small paint sample cards of different colors from Lowes and WalMart in my camera bag to play with the custom white balance.

Like these two of the same sunset:
//www.sabphotography.com/bluetree.jpg
//www.sabphotography.com/redtree.jpg
 07/14/2005 11:07:54 AM · #11
Gray cards are for reference shots when shooting RAW during any time you are in the same light. A white card is for setting a custom WB at the beginning of a shoot and would subsequently need to be changed if the light changes. In Post Processing you can get the accurate WB on a gray card shot by putting the eye dropper on the gray reference shot. A Gray card is more convenient because you can use it any time during the shoot without concern as to the WB setting, (A,SUN,SHADE,CLOUDY,FLOURESCENT,TUNGSTEN)as reference (if you are shooting RAW) and then adjust easily in post. If you are shooting in JPEG then you would want to use the custome PRE WB with a white card, because any change you made in post would be throwing away pixels, but you would also have to re-PRE if there were any variations in settings/light. Your camera takes pictures in Black & White and the color is added by software in your camera using RGB filters (depending on model) With a White card what you are doing is telling your camera This is what white looks like in this light so it has a point of reference to add color accurately. Again, if shooting RAW it wont matter, If shooting JPEG you want it right from the beginning and must change constantly due to the nature of the format. As others have pointed out though, you can experiment with other color cards...Rules are made to be broken..

I hope I made sense here.

Watch these and maybe you can understand it better, or read Real World Color Management
 07/14/2005 11:13:01 AM · #12
Originally posted by deapee:
Good samples, great write-up. That should be a tutorial.


I just thought the same thing. Great tutorials for newbies. I remember when I got my white and grey card and read directions.....I made no sense to me!! This is an excellent step by step with pictures!!
 07/14/2005 11:15:51 AM · #13
Originally posted by sabphoto:
If I understand it correctly, the camera adjust whatever you point it at to try and make it a neutral white (actually it's like 15% gray). So either will work. For some cool effects point the camera at something red and do a custom white balance.

I carry small paint sample cards of different colors from Lowes and WalMart in my camera bag to play with the custom white balance.

Like these two of the same sunset:
//www.sabphotography.com/bluetree.jpg
//www.sabphotography.com/redtree.jpg


Is that how you got the different background? Just by setting your custom balance to the different paint cards? Clever! May seem simple...but I would have never though tof that!!!

07/14/2005 11:23:04 AM · #14
This thread discusses it also.

Just a note on my post above...this is only my understanding and certainly not written from an authoritative standpoint...sometimes I come off like that and dont mean to. I am but a humble student of the many more-experienced people here.
 07/14/2005 12:04:02 PM · #15
Originally posted by colyla:
Originally posted by sabphoto:
If I understand it correctly, the camera adjust whatever you point it at to try and make it a neutral white (actually it's like 15% gray). So either will work. For some cool effects point the camera at something red and do a custom white balance.

I carry small paint sample cards of different colors from Lowes and WalMart in my camera bag to play with the custom white balance.

Like these two of the same sunset:
//www.sabphotography.com/bluetree.jpg
//www.sabphotography.com/redtree.jpg


Is that how you got the different background? Just by setting your custom balance to the different paint cards? Clever! May seem simple...but I would have never though tof that!!!


Yep, my camera allows me to save 4 custom white balances for anytime use. I have a blue, green, orangeish yellow, and red. I have used the orange to add a little sunrise and sunset but it sometimes adds way to much and it changes EVERYTHING in the image not just the sky. The examples I posted are before I started using RAW so some adjusting could have been done there too.

Message edited by author 2005-07-14 12:04:16.
 07/14/2005 12:29:56 PM · #16
Thanks to all so much... this has been very helpful.
I've played with my camera as I shoot mostly JPG at this point, and I do find it very useful to use the custom white balance.
I did notice however, that in situations where you have mixed lighting you could get in real trouble. For example if I am shooting indoors and adjust WB according to whatever lighting I have indoors, I noticed that any light that comes from outside will add a strong bluish cast... so part of the photo will be right on as far as WB and then there will be parts that will be bluish, like around windows...etc
07/14/2005 12:42:34 PM · #17
Originally posted by WhidbeyPix:
I did notice however, that in situations where you have mixed lighting you could get in real trouble. For example if I am shooting indoors and adjust WB according to whatever lighting I have indoors, I noticed that any light that comes from outside will add a strong bluish cast... so part of the photo will be right on as far as WB and then there will be parts that will be bluish, like around windows...etc


Yes, and as you stated, setting the WB will not resolve the mixed lighting situation. If you set it to indoor, then outdoor light will give a blue cast, if you set it to outdoor, then indoor will add a yellow/orange cast.

Might be a great reason to check whether converting the image to black and white will give a good result. In that case color temperature of light sources will not bother you.
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