OK folks..time to step out and show my lack of knowledge. I know a grey card is used for white balance but I'm unsure how to use one. Someone teach me please!
There is some evidence that in order to set color and white balance you are better off using a calibrated white target. A gray card is preferred to set an average exposure.
The difference is that the white target will provide more data from which to measure color neutrality. This partly because the camera's imager will contain more data close to saturation, 255, 255, 255 (in 8 bit parlance. More bits equates to even more data.) More importantly is that the image will contain most of its information in the first 2 stops of highlight data.
If you expose the white target at just a bit below saturation of any color channel, you will have more data to work with than a gray target and the extra data yields greater accuracy.
This is especially important in white balance situations like tungston where a color channel will naturally be suppressed.
great article! do you know if you can save white balance levels as presets in Lightroom 3 too? I'm in the beginning stages of learning that too!m So much to learn...so little time!
Also, don't use an old 18% grey card that was manufactured before digital cameras became prevalent. Trust me, they are still sold. They are not all really neutral. They were intended to provide an 18% grey for metering, and were never really intended for setting white balance. Get something like a Lastolite or Photovision digital calibration target.
John :
Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.
Like John said, a standard cardboard "traditional Kodak grey card" was to be used with the exposure meter in your camera ( or a handheld meter ) for exposure settings, it was never designed for setting color temperature. It frequently reads a bit to the red side of the spectrum I think.
A WhiBal card, a Lastolite Color Balance Reflector or a few other devices were designed with color balance in mind, and work quite well. Typically a WhiBal card is included in an image that you are shooting, such that it receives exactly the same lighting as the subject, and this card area is then used in LR or PS to set a white balance for the image in your post processing software.
The Lastolite Color Balance Reflector can be used this way also, but is not ideal. It is designed to be shot in the ambient light at the time of shooting, to capture an entire frame as a neutral gray image. This is done by shooting a frame of the surface of the reflector with the camera in Av mode. This will produce a grey image with the histogram of the red, Green and blue channels all as a single spike in the center of the histogram display. This jpg is then used in your camera's menu setup to create a custom white balance for the camera to shoot color balanced jpgs ( or Raw files too ) and it does this very well.
One of the nice things about the Lastolite Color Balance style reflector, is that you can see if you have a true neutral grey image because your camera's histogram will be three individual spikes that overlap in the exact center of your histogram. This proves the image is a true color neutral, and also tells you that the exposure was dead accurate as well. Otherwise the three channel spikes would be to the right or left of center. Hence with one frame you can get color balance information AND accurate exposure information as well. Accurate exposure is needed if you hope to capture a full ramp of the tones of a grey stepped image like I show in the link I posted.
I recently purchased a WhiBal card from Michael Tapes Design (Google for website).
I bought the G7 Pocket Card for $19.95. Fantastic!
I've been shooting some table-top shots of some antique crystal perfume decanters
and other small pieces. The set-up is tripod-mounted camera and shooting the
object in a home-made light box with external incandescent lights.
I put the WhiBal card in the first shot and then remove it for the others. I've
processed the images both in Photoshop CS4 and in Lightroom2 to see the results
using Curves in CS4 and the WB eyedropper in LR2. Instant accurate color rendition.
The images were far too warm (yellowish crystal) before the adjustment.
I can use a pre-set or Save Curve, on the balance of the shots, but it's simpler just
to note what the Color Temp is in adjusted image and replicate that.
I haven't used it outside, but color accuracy isn't as much as a problem with natural
light.
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The difference is that the white target will provide more data from which to measure color neutrality. This partly because the camera's imager will contain more data close to saturation, 255, 255, 255 (in 8 bit parlance. More bits equates to even more data.) More importantly is that the image will contain most of its information in the first 2 stops of highlight data.
If you expose the white target at just a bit below saturation of any color channel, you will have more data to work with than a gray target and the extra data yields greater accuracy.
This is especially important in white balance situations like tungston where a color channel will naturally be suppressed.
See the following threads for more information:
http://www.dgrin.com/showthread.php?t=94149
http://www.dgrin.com/showthread.php?t=90438
Moderator of the Cameras and Accessories forums
great article! do you know if you can save white balance levels as presets in Lightroom 3 too? I'm in the beginning stages of learning that too!m So much to learn...so little time!
Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.
A WhiBal card, a Lastolite Color Balance Reflector or a few other devices were designed with color balance in mind, and work quite well. Typically a WhiBal card is included in an image that you are shooting, such that it receives exactly the same lighting as the subject, and this card area is then used in LR or PS to set a white balance for the image in your post processing software.
The Lastolite Color Balance Reflector can be used this way also, but is not ideal. It is designed to be shot in the ambient light at the time of shooting, to capture an entire frame as a neutral gray image. This is done by shooting a frame of the surface of the reflector with the camera in Av mode. This will produce a grey image with the histogram of the red, Green and blue channels all as a single spike in the center of the histogram display. This jpg is then used in your camera's menu setup to create a custom white balance for the camera to shoot color balanced jpgs ( or Raw files too ) and it does this very well.
I wrote about both techniques here
One of the nice things about the Lastolite Color Balance style reflector, is that you can see if you have a true neutral grey image because your camera's histogram will be three individual spikes that overlap in the exact center of your histogram. This proves the image is a true color neutral, and also tells you that the exposure was dead accurate as well. Otherwise the three channel spikes would be to the right or left of center. Hence with one frame you can get color balance information AND accurate exposure information as well. Accurate exposure is needed if you hope to capture a full ramp of the tones of a grey stepped image like I show in the link I posted.
Moderator of the Technique Forum and Finishing School on Dgrin
I bought the G7 Pocket Card for $19.95. Fantastic!
I've been shooting some table-top shots of some antique crystal perfume decanters
and other small pieces. The set-up is tripod-mounted camera and shooting the
object in a home-made light box with external incandescent lights.
I put the WhiBal card in the first shot and then remove it for the others. I've
processed the images both in Photoshop CS4 and in Lightroom2 to see the results
using Curves in CS4 and the WB eyedropper in LR2. Instant accurate color rendition.
The images were far too warm (yellowish crystal) before the adjustment.
I can use a pre-set or Save Curve, on the balance of the shots, but it's simpler just
to note what the Color Temp is in adjusted image and replicate that.
I haven't used it outside, but color accuracy isn't as much as a problem with natural
light.
http://tonycooper.smugmug.com/
'Till you're shooting under a green tree, or against a funky colored wall.
Natural selection is responsible for every living thing that exists.
D3s, D500, D5300, and way more glass than the wife knows about.
What color is a could over a cornfield in Iowa???
Moderator of the Technique Forum and Finishing School on Dgrin