Thursday, July 18, 2013

And now, a word about White Balance....

My last post here (I think I must be on a summer hiatus?) discussed Picture Style; the differences among them, and which of them was most appropriate for intraoral imaging. Now I'd like to take a closer look at White Balance, which can just as easily be a source of some confusion for the non-professional shooter.
White balance (sometimes called gray balance, or color balance; all the same thing) refers to the process of removing an unwanted or unnatural color cast in a scene so that objects that appear white to our eyes will look white in the photograph. Our eyes are great compensators and will correct for environmental conditions, reflections, color temperature, and so on, but unless we make those  adjustments in our camera, we'll get poor color images that are difficult to correct in post-processing. This is much easier to do with digital cameras than when we were all using film and our options were much more limited.

Here's a good example of that. Viewed individually, we may not see anything terribly "wrong" with any of the pictures of this lady with a guitar, but side-by-side we can make a more critical assessment. While the image in the middle has more natural and neutral tones, the one on the left is distinctly "warm" (strongly tending towards the reds and yellows) and the one on the right appears distinctly "cool" (tending more towards the blues and greens).

Now let's look at how we control for this in the camera settings:

AWB: Auto White Balance; this mode calculates an average color temperature for an entire scene. While I often find this problematic in a scene that has multiple sources of light, each with its own strong influence, it works well with one dominant light source -- as when we are shooting intraoral images using a ringflash. I typically use this mode for exactly that reason. In the sample above, and in the following, the color chart on the left was shot using available, natural daylight. The ones on the right are shot using on-camera flash.
DAYLIGHT: usually useful for making available-light exposures on bright, sunny days. (Since I live in Oregon, I probably don't get to use this one very much!)

SHADE: open shady areas on an otherwise sunny day with blue sky will tend to shoot somewhat cool, so this mode adds more reds and yellows to the scene.
CLOUDY: This may be a bit more Oregonian (maybe with a little rain?).  Here, too, the thought is that cloudy days produce cooler exposures, so this warms it up a little. You can certainly use this anytime on a sunny day if you like a slightly warmer touch to your pictures. Everything is worth experimenting with.

TUNGSTEN: Have you ever seen old photographs that were taken indoors, and they all look intensely yellow? That's because color film was usually "Daylight" balanced, and common light bulbs -- tungsten bulbs -- produce a low color temperature, yellow-orange color cast. This camera setting compensates for that.

FLUORESCENT: Traditionally, fluorescent lighting was distinctly magenta-blue, in the same way that tungsten lighting is distinctly yellow. However, most modern fluorescent bulbs are now designed to produce a more natural color balance.

FLASH: Most on-camera flash units produce a color temperature at or above 6000K, which is cooler in tone than standard daylight, so this setting adds some warmth. In practice, I find this usually adds too much warmth, and flashes can vary quite a bit in color temperature as well, so I rarely if ever use this.

These last two settings in your White Balance menu are CUSTOM and, below that, KELVIN setting.  Photographers will frequently "custom balance" their jpeg images to minimize post-production time when shooting a large number of images under the same lighting conditions (think outdoor wedding). This can often improve the overall color quality as well, but intraoral images made with  the macro lens and ringflash cannot be custom white balanced.
And finally, setting an actual Kelvin value can be useful in creating precisely defined color images. This is very useful to commercial photographers.

Since we're on the subject of color, on my next post I'll try to discuss in greater detail some of the broader color issues like color temperature and environmental effects on how we perceive and record color information. In the meantime, play with your camera and experiment with these settings. You can't break anything, and you'll have fun looking at the different results you can end up with.

And post your pictures -- and questions -- right here!

Later, amigos!