photography

[gusl]

When I took this picture:


I was not satisfied with the color of the sky: the sky in front of me was purple, but my camera seemed to see it otherwise.

Then I took another one, further up in the sky:

and the color seems to be somewhat more faithful.

Why?

Comments

[0436.livejournal.com]

GREEN MONSTER

[gustavolacerda.livejournal.com]

care to explain your jargon?

[gregh1983]

I suspect it has to do with your camera's automatic exposure settings. In the first shot, most of the frame is filled with the (comparatively dark) building, which your camera is going to use as its base for determining the exposure. Since the building's relatively dark, you probably got a relatively long (or wide open) exposure that lightened the sky too much. In the second shot, the sky takes up more of the frame, so the camera is basing its exposure on that; the result is a more properly exposed sky, but a darker building.

The best way I've found to draw out sky colors around sunset is to set the camera to purposefully underexpose by a bit. You can probably figure it out for your camera based on the instruction manual. Another possibility is to see what shutter speed and f-stop your camera's selecting by default, put it into manual mode, and then increase the f-number or (the denominator of) the shutter speed from there.

[gustavolacerda.livejournal.com]

That makes sense. Thanks!

[gregh1983]

No problem :-) Hope it helps!

[gustavolacerda.livejournal.com]

I'd love to see the function they use to compute the exposure time. I wonder if it's based on the mean brightness.

One should be able to settle this by doing a few experiments, together with knowledge of optics. The first few experiments would measure the brightness of different colored objects by taking picture where the objects are a small part of the image. Knowing their luminosity, take pictures where the objects appear very large, and see how bright they appear.

[the-locster.livejournal.com]

"I'd love to see the function they use to compute the exposure time. I wonder if it's based on the mean brightness."

Depends on how old the camera is. I would expect for a lot of recent cameras the exposure logic is tied in with the autofocus logic - thus setting the exposure based on the brightness of the area being used to set the focus, e.g. a person in the foreground, or in your case a building.

Autofocus appears to have gotten a lot cleverer recently with some cameras having face recognition for this purpose.

Anyhoo, if the picture doesn't come out right just post process it :) The GIMP has some nice filters/effects.

[gregh1983]

thus setting the exposure based on the brightness of the area being used to set the focus

I believe on mine they're actually separate. I have mine set to get the metering from the whole frame but to only focus based on what's in the center. (I find it easier to recompose the image manually than have the camera pick a focus based on stochastic black magic.) But it's probably camera-dependent. I think old manual cameras generally had the light meter in the middle.

[en-ki.livejournal.com]

The keyword you're looking for is metering: the camera is trying to make the whole scene have the same average luminosity as a 12% gray reference image, but various metering modes will try weight the average in different ways. Exposure compensation will adjust the target average.

(Incidentally, using flash mode is a pretty good way to get pictures of fireworks and stars if your camera won't do manual mode and can't reach far enough with exposure compensation: the flash is wasted, but you get a very short exposure despite the dark, which lets you capture the small bright areas you wanted.)

[gustavolacerda.livejournal.com]

Also, this misprediction explains why you shouldn't use flash when photographing faraway objects (mountains, etc). They will appear darker than intended... unless the camera's hardware computes faster than the duration of the flash.

[the-locster.livejournal.com]

Again, a decent modern camera will disable the flash if the autofocus has chosen a point in the distance to focus on. In fact I usually disable the flash to get pictures with truer colours - a flash washes colours out, eliminates any nice shadows, highlights blemishes in people's complexion. Improved CCDs and anti-blur techniques seem to make up pretty well for the increased exposure time.

[theadana.livejournal.com]

That was a great explanation... I've always wondered about that, too!

[altamira16.livejournal.com]

If you have a digital camera, some of them let you set the metering to be spot, area or multi-metering. Though the terms seem slightly different here, it may be worth a read.