plum:Obscura...or anyone who can help.... I just purchased the digital gray card you recommended and hopefully will get it next week. I have not used one.. so like others.. not sure the exact steps.. after I take a picture of the gray card, then what?
There are two schools of thought on using gray cards for custom white balance. One is to fix it in your raw conversion and the other is to set a custom white balance and then check and adjust if needed in post. Both ways work but I prefer setting a custom white balance so things are correct or very close to correct when I get ready to do my raw conversions.
Here is how I work:
You'll need to check your camera' s owners manual because setting the custom white balance is different in different cameras.
- Compose your scene and set up your lighting.
- Use a flash meter or your histogram to determine proper exposure.
- Place your gray card in the scene so it is being lit just like your subject. (If I'm doing portraits I have an assistant or my subject hold the card right under their chin so it's being lit just like their face is)
- In my camera I activate a menu item to "set custom white balance"
- Move in so the gray card is filling the frame (or filling the center target area in your viewfinder, it's different with different cameras) and press "OK" to capture custom white balance. If successful, the camera gives me a message saying so.
- After setting the custom white balance my camera assumes that I want to use it. If your's does not do this you'll need to tell your camera to use the custom white balance that you just captured.
- re-compose and shoot a reference image with the gray card in the scene. (exactly where it was when you captured the custom WB) It is very important to capture a reference image. This is how you will check your work and adjust if needed later on.
- Remove the gray card and continue shooting. Your ok as long as the lighting does not change. New lighting conditions will need a new custom WB.
- Finish shooting
- Now open your reference image in your raw conversion software and check the RGB levels of the gray card. If they're all the same, it's gray. (R=G=B=GRAY) Now I say all the same... they may be a point or two off on some parts of the gray card. The important thing is that they're all within a point or so.
- If the RGB levels tell you the gray card is gray, you've captured good color. Go on about your business and convert your images :-)
If something has gone wrong and the gray card has a color cast:
(or you don't like custom white balance and prefer fixing everything in post)
- I'm checking my reference image and the entire family dressed in red sweaters must have reflected red off the ceiling creating a red color cast in the entire image. (including the gray card in the reference shot)
- My raw conversion software has an eyedropper tool for setting the white balance. I activate this tool and click on the gray card in the reference image. This tells the software that what I've clicked on is supposed to be gray and to make it so. In the process of doing this it shifts all of the other colors in the image so everything is correct.
- I save this white balance adjustment and then apply it to all of the other images that need the same correction. (the ones without the gray card)
This might seem like a difficult process but it really is amazingly simple. I've been doing it so long that it's second nature.
Note: It is also important to note that because I'm going strictly by the RGB values the monitor that I'm working on does not even need to be calibrated.
Also Note: Perfect color isn't always the best color. It's a great place to start. I photographed a 4 day old baby with jaundice once. If I had given the parents "perfect" color they would not have been thrilled. If the perfect color is not working do not be afraid warm things up or cool them down to convey the mood the way you want to.
Hope this helps! Join the Gray Card Army!