18% grey card or white paper ?

In the 20D manual custom WB is done photographing a "white object" in the present light. I read elsewhere to use white paper, there are different shades of white. I read in another place to use a 18% grey card. I set my WB useing a white piece of printer paper and it made a huge difference in the quality of the pic I was taking,(for the better), in artificial light. My question is where does the 18% grey card come in?


JZ

You should use a grey card to assesss exposure as exposure meters are usually set to meter 2correctly" using an 18% reflectance value off an "average" scene. So in tricky lighting a 18% grey card, lit as the scene is lit can be more accurate than trusting to the scene value.
In addition most grey cards have a 90% (?) white on the reverse which is ideal for WB setting.
Really a grey card should be in every photographers camera bag.

A standard 18% grey card is color-neutral. If you were to use a slightly off-white (off-neutral) card for your custom white balance, that color would have a slight impact on the correction applied, since the camera would be trying to remove the, say, beige, from the card's pigment as well as the, say, orange, from the prevailing light. Result: overcorrection.

It really doesn't matter what shade of white (and grays fall in this category) you use as long as it is neutral.

I use a 18% gray card for all my studio work, for both exposures and my white balance. I was tempted to print a 18% gray sheet in my inkjet, but after some thought, forked up the $$$ for a real gray card, worth the (not much really) money.

Has anyone had any issues with the cards fading? I always keep mine in the opaque bag it came in when not in use, just in case.

Jerry, I did an experiment last year with my 10D. As I just got my 20D this week, I haven't had time to repeat that experiment. I saw a difference between grey and white CWB's. I did this experiment because I had seen both ideas of grey or white CWB floated around in various places and I decided to see if I could see a difference.

On a clear, blue sky day, I mounted my camera on my tripod and did a CWB with the 18% grey side of the Kodak Grey Card. I then set the 10D to use that CWB and took a landscape shot that had a variety of colors. I immediately repeated the procedure using the white side of the Kodak Grey Card. I shot the photos in RAW format. I used BreezeBrowser to convert the RAW images. The resulting images looked almost identical except that the photo taken with the white card CWB had a bluer sky that more clearly looked like what the sky actually looked like when I took the photos. BreezeBrowser was set up with default values as I had just recently bought it at the time. BreezeBrowser uses the Canon libraries.

I repeated the experiment on a cloudy, overcast day. In this case I saw no differences that I could perceive.

This was certainly not an exhaustive test and there is my perceptual subjectivity to contend with, but I suggest that you may want to try a similar experiment yourself (unless others demonstrate a significant oversight in my methods). I now use the white card because of my results and the Canon recommendation of a white card.

FlyingPete: I haven't noticed any fading myself. I cut up one of the 8x10 Kodak cards into 4 - 4x5 cards. I keep them in my camera bag (in a plastic baggie). If I get dirt on my working card I will have a replacement available.

The "proper" thing to do is use grey for metering and for digital WB use a pure white card. However, there are situations that due to special circumstances a colour might be reflected on to the white card which might give you an incorrect WB reading. In that situation you can try to use your grey card to set your WB. I would only suggest using grey as your WB in special situations. Use white all other times.

Mine's something over 20 years old, lives in a manila envelope now that Kodak's original paper envelope wore out, and isn't showing signs of fading.

The density of the card doesn't matter for custom white balance just so it's neutral. Your meter is going to expose it to a middle grey regardless of whether you use a white, grey, or black card.

A grey card is just a dark white. Under expose white and it will look grey. If you have grey or white with no colour cast it shouldn't make any difference to the white balance setting. Since Canon recommends white, that is what I generally use.

Various 'white' papers can look quite different. Many times white paper has a slight blue tint, to make it look brighter, so that would make a picture warmer (if WB done on that paper). This might make it look 'better' subjectively, especially in an indoor scene, where we expect warm light.

This once gave me an idea to have three cards for white balance, a slightly blue card, if I wanted a warm bias, a neutral one, and a slightly yellow one for a cold bias.

Never tried though, in reality I could probably do away with the yellow one, as I have not yet needed to make an image 'cooler'.

I shoot wedding so white balance is critical. I have found that coffee filters [the white ones ] work really well. The tuck in my pocket and camera case easily. The cards are great but I never have it on me when I need it. tt

Finding neutral white paper is pretty difficult. I eventually made up a wb target made up of equal amounts of both slightly cool and slightly warm. The resulting balance is as near neutral as makes no difference. My target is pocket size at 5 inches square. Shoot the target so it occupies an area a bit larger than the centre circle and use the shot's wb as a reference during raw conversion. If you prefer shooting jpeg, use the shot to set a custom wb for the conditions that prevail at the time.

OK, you guys have me thinking about doing custom white balance now. I have two questions:

1. Since I have a 20D, once I set CWB, how much of an ordeal is it to reset back to default just for WB, or do I have to reset the entire camera? Or will I now have to set CWB for evry picture from now on?

2. Where can I get a cheap pure white card? The places I've seen over sets or systems...

All you have to go to change the WB from custom is move it to one of the other settings. If you go back to custom, it will be the last CWB set.

B&H has gray cards with white on the other side for 10 or 15 dollars.


Jeff