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Archive for October 3rd, 2009

Digital Photography: Sometimes Underexposure Is Your Friend

Took some pix of the high school marching band yesterday and the whole lot came out one stop underexposed… exactly as I intended.

Their uniforms are dead black wool with a yellow left-shoulder flap. The camera looks at all that black, desperately attempts to make it neutral gray, and blows out all the highlights. Given that the only highlights are the face and hands, the absolutely critical part of the image looks awful.

Auto Exposure

Auto Exposure

The first picture (a small crop from a much bigger image) shows what the auto-exposure algorithm comes up with:

Exposure Bias : 0
Exposure Mode : Auto
Exposure Program : Auto
Exposure Time : 1/1000 s
FNumber : F4
Flash : No, auto
Focal Length : 60.1 mm
ISO Speed Ratings : 125
Light Source : Daylight
Metering Mode : Center weighted average

Notice the burned-out highlights: the left hand is flat, the clarinet keys reflect retina-burn white, and the yellow shoulder is monochrome.

Under those circumstances, the only thing to do is override the camera’s opinion and force some underexposure. You can either meter each shot manually or just tell it to knock the auto-exposure back a bit. I generally choose the latter, if only because the camera comes up with a reasonable approximation of a good exposure faster than I can. If I don’t lay the center-weighted spot on the black side of a uniform, that is.

Minus 1 stop

Minus 1 stop

So the second picture (another small crop) is “underexposed” by a stop:

Exposure Bias : -1
Exposure Mode : Manual
Exposure Program : Auto
Exposure Time : 1/1250 s
FNumber : F5.6
Flash : No, auto
Focal Length : 60.1 mm
ISO Speed Ratings : 125
Light Source : Daylight
Metering Mode : Center weighted average

Much better.

We can quibble about the color quality, but at least the highlights aren’t blown out and there’s some texture to the uniform. The black part of the uniform is a dead loss, but that’s pretty much the way it’s got to be: the camera simply doesn’t have enough dynamic range to handle a dead-black uniform and glare-white reflections.

One of the band members has absolutely gorgeous deep-dark-brown skin that I have yet to get right. Either the highlights burn out or her skin blends into the shadows. Twiddling the gamma doesn’t help much.

More on the details of why you want underexposure, even in what look like evenly illuminated scenes is there.

Sometimes, though, you just gotta fix it in the mix, as described there.

Memo to Self: Set the color balance to “daylight”, too, because bright primary colors against black can be confusing.

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