Gray Card vs White Card

[mkies]

My goal is to do the least amount of post digital processing as possible. Thus, I need to properly expose, set the white balance, and set a color reference within a picture.

I know a gray card can be used as a color reference within a picture. That is, if you know that you have a perfectly gray source within the picture, you can use Photoshop ('set gray point') to click on this gray point and the rest of the colors should be very accurate within the picutre.

I also know a white card can be used to set the color temperature of the scene by using a custom function within the 10D. Again, a reference shot is taken with the white card to set the custom setting.

My question is this. Can I only use a white card to get both the color temperature right and have a color reference within the picture? There is a 'set white point' also within Photoshop, and if I only have a white reference, does this do the same as only using a gray card as a color reference?

I know pure white and black are 'shades of gray' with equal RGB intensities. What then is the point within Photoshop to have the set white, set gray, and set black points?

Bottom line: is it possible to set both a color reference and white temperature by only using a white card? On the surface, this would seem OK to do (it would save a step in the pre processing step), but I need some additional input/comments or if I am way off base here.

Thanks in advance!

Martin

[Roger_Cavanagh]

Martin,

Setting white balance and colour temperature is the same thing. The different white balance settings in the 10D are just different temps.

You can use a white card as the manual says, but many people advise using a gray card because you are less likely to get over-exposure with the gray card. There is also a school of though that says a 3/4 tone gray is better than the mid-tone gray of the standard Kodak gray card.

You can use any neutral colour - shade of gray - to get the same results, but it's a good idea to avoid very dark or very light shades.

Regards,

[stopbath]

Your kodak grey card will have white and grey sides to it.

You can use any side for colour balance (colour temperture). Since Grey is only a darker shade of white, both will work fine, though white may give the camera bigger values to work with.

[MediaMagic]

Here's a link to a filter like lens attachment which allows you to set the white balance as close to perfect as you can get with the custom white balance. Dans_D60 sent me this link in another thread and I ordered one to see if it really works. Yes, it does. Very easy to carry as it fits right in a filter case with your other filters. It doesn't screw onto the threads but rather snaps or grabs into place. And since it completely covers the glass, it makes shooting a "greycard" completely foolproof (for us fools). It's quite a bit more expensive than a piece of paper, but I like being able to whip it out of my pocket and get an accurate white balance in a matter of seconds whenever the light changes. You can also throw it on the lens and then throw another filter on top of it and get the balance through the filter. It comes in sizes from 49mm to 82mm I think it was, but if you like it, all you need is to get one that fits your largest lens and just hold it in place over the smaller ones. It's pretty darn cool I think. But then again, I'm often dazzled by bright shinning objects too.

http://www.expodisc.com

I'm very pleased with it...

Take care,
David

[jjeff]

Your kodak grey card will have white and grey sides to it.

You can use any side for colour balance (colour temperture). Since Grey is only a darker shade of white, both will work fine, though white may give the camera bigger values to work with.

hi. Stopbath,

hope you are still logging on here to see this... :)
what do you mean by this? what "bigger values" do you mean?

jeff

[PhotosGuy]

what "bigger values" do you mean? The same exposure with the white card will move you farther to the right in the histogram than the gray card would in the same light. Keep in mind that you don't want to be ALL the way to the right for WB - the cam needs some unblown pic info to work with.

[Peter_Photo_Guy]

You may want to check out Perfect-Pixs 3 Card Kit. I got iton EBay and use it instead of my gray card. The kit included a gray zone card, a white card and a colour patches card.
Pete

[Robert_Lay]

Your kodak grey card will have white and grey sides to it.

You can use any side for colour balance (colour temperture). Since Grey is only a darker shade of white, both will work fine, though white may give the camera bigger values to work with.

Question - why would a white card give a bigger value than a gray card, if the lightmeter sets the exposure to render each of them to the same shade - namely middle gray???
:rolleyes:

[Robert_Lay]

My goal is to do the least amount of post digital processing as possible. Thus, I need to properly expose, set the white balance, and set a color reference within a picture.

...

Martin

Dear Martin,

Tutorial on Use of the Gray Card for Exposure and White Balance:
http://www.zaffora.com/W9DMK/GrayCardTutorial.htm
or the downloadable PDF version:
http://www.zaffora.com/W9DMK/GrayCardTutorial.pdf

Hope the tutorial will provide a little better understanding of the basics.

[PacAce]

My goal is to do the least amount of post digital processing as possible. Thus, I need to properly expose, set the white balance, and set a color reference within a picture.

I know a gray card can be used as a color reference within a picture. That is, if you know that you have a perfectly gray source within the picture, you can use Photoshop ('set gray point') to click on this gray point and the rest of the colors should be very accurate within the picutre.

I also know a white card can be used to set the color temperature of the scene by using a custom function within the 10D. Again, a reference shot is taken with the white card to set the custom setting.

My question is this. Can I only use a white card to get both the color temperature right and have a color reference within the picture? There is a 'set white point' also within Photoshop, and if I only have a white reference, does this do the same as only using a gray card as a color reference?

I know pure white and black are 'shades of gray' with equal RGB intensities. What then is the point within Photoshop to have the set white, set gray, and set black points?

Bottom line: is it possible to set both a color reference and white temperature by only using a white card? On the surface, this would seem OK to do (it would save a step in the pre processing step), but I need some additional input/comments or if I am way off base here.

Thanks in advance!

Martin
What you want to use is the gray card. You can use it to set the exposure and custom white balance, both without having to fiddle with anything, including the exposure. If you use the white card, then you'll need to add +EC or set the camera to manual mode and adjust the exposure accordingly. No need to do that with the gray card.

[PhotosGuy]

Question - why would a white card give a bigger value than a gray card, if the lightmeter sets the exposure to render each of them to the same shade - namely middle gray I'm guessing that stopbath means that in very low light, the exposure might be 1sec vs 4 sec white/gray. I haven't checked with digital, but I grew up with meters that weren't all that accurate reading 4 sec exposures, too, so I'm comfortable with a white reference. If you use the white card, then you'll need to add +EC or set the camera to manual mode and adjust the exposure accordingly.
Right. As an old manual guy, I actually prefer it over EC which also takes time to adjust. And I can adjust M without taking my eyes off what's happening.
Everyone works differently, which is why it's nice to have choices. ;)