Custom WB using 3 color cards

Started Jul 5, 2013 | Discussions thread
Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 11,807
Re: Custom WB using 3 color cards

er3 wrote:

So I was thinking about getting an 18% gray card to set custom WB. BUt saw these 3 color WB cards. Are they used the same way? As in you zoom in, take a pic & then set the custom WB in camera? Or are these just for post processing?

If the three colors — can I assume they are white, gray, and black? — if they are neutral, then you can use one for white balance. I’d use the white one.

The way the card is intended to be used is this:

  • Take a photo with the card in the image, making sure that the white part is not overexposed, and the black part is not underexposed. Be sure that the card is facing the camera directly, and has the same lighting as the main subject.
  • Without changing anything in the scene, without moving the camera or subject or lighting, nor changing the exposure or white balance, take another photo of your subject without the card.
  • In post processing, use curves to force the white part to be near pure white — maybe an RGB value of (240, 240, 240). 
  • Do the same to the black part, setting it to about (25, 25, 25). 
  • And do likewise to the gray part, setting it to about (128, 128, 128).
  • These are guesses on my part: your manual might recommend other values.
  • Apply those same curves on the photo you took without the card in it. You should get a nice tonality and white balance on your image. 

This is one of those calibration steps which might be critical for good work, but may become less necessary as you gain experience.

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