Why doesn't Aperture show black as black?

Question

Aperture seems to be displaying my images brighter than they actually are -- this makes colors seem washed out and makes it very difficult to accurately adjust the black point and other exposure parameters.

Here's a screenshot:

Notice that the loupe (set to the same magnification as the zoomed-in image) is more saturated, and blacks are blacker than the surrounding image.

Also compare the bottom edge of the image to the black strip just below it.

This happens even for totally black images, and is independent of any image adjustments:

Why is Aperture messing with my colors like this? How can I fix it?

Answer

You've accidentally turned on Onscreen Proofing, which is used to simulate the colors of a final output medium like CMYK ink on paper. Turn it off by going to the View menu and clicking Onscreen Proofing, or hitting Option-Shift-P

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How can I meter to get a black object black?

Question

If I have something in my scene that I want rather close to pure black - can I spot meter off the object and then adjust the exposure by a consistent, pre-defined number of stops to get black instead of gray? I'm aware the rest of the scene may be off, but if my goal is that object - is it possible?

Answer

Yes. Spot metering gives you 18% grey. Each stop below that halves the reflectance.

The number of stops to dial-in depends on how close to black you want the result and the dynamic range of your camera.

With a perfect noiseless exposure, -1 EV would give you 9%, -2 would give 4.5%, -3 would be 2.25%, etc. As you can imagine, most cameras are not perfect and there is such thing as a noise-floor. If you exposure below this, then all details get drowned by noise.

The best thing to do it to experiment and figure out the value of your camera. Unless you are shooting RAW, the number of stops depend on image parameters, mostly Contrast and High/Low key if your camera has them. For fixed image parameters and ISO, your that value will be fixed for your camera.

Most Olympus DSRLs and SLDs have a metering mode called Spot Shadow which is designed to exposure something very dark while retaining details. It is equivalent to normal Spot metering -3 EV. Doing the same using EC with your camera is probably what you want.

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