There are shortcuts, but they don’t all work on all cameras.
One way to get the same information in all channels is to balance to an image where all the pixels are at maximum or minimum. Nikons usually refuse such images as invalid, but this will reportedly often work on Canons. Try taking a picture of the inside of the lens cap or dramatically overexpose a picture of almost anything. To see if you have achieved the desired white balance, look at the red and blue white balance coefficients in the camera’s EXIF data. They should be within five or ten percent of one.
Another shortcut is to use the manual white balance settings to set the white balance to about 3800 K and the color bias as green as it will go. After you do this, make some test exposures and look at the EXIF white balance coefficients. You can tweak the coefficients by adjusting the manual white balance settings. Many cameras don’t have sufficient range in their manual white balance settings to get you all the way to UniWB.
Yet another quick way to get to UniWB in a camera that allows you to copy the white balance setting from an image is to get a copy of an image from that camera with UniWB all set up. You just copy the image to a memory card, but it in the camera, and tell the camera to use the white balance coefficients from the image as a white balance preset. Be sure to name the file in a way that the camera will recognize it as its own.
In value engineering, the first step you consider is eliminating the function. In that spirit, one way to shortcut UniWB is to not do it, but to use some other technique for ETTR. If you’re pretty sure you know where the brightest spot in the image is, and if, as is the case of most highlights, not highly chromatic, you can meter it to set your exposure, and ignore the histogram in the camera. There are several ways to express this metering technique, and different formulations speak to different photographers:
- Meter the highlight and open up three stops
- Place the highlight on Zone VIII
- Set the exposure compensation to +3 stops, and meter the highlight
All of the above are equivalent. I don’t use this technique because I doubt my ability to find the highlight, and find it slower than snapping off an image and looking at the histogram.