Sunday, July 11, 2010

HDR fun

Here's a picture that may not look very interesting.

What's the point, right?

Well, here's what a picture of that view looks like, straight out of my iPhone 4's camera:

The sunlit view out the window is way too bright, resulting in massive blow-out of the image.

Ok, well tell the camera to ramp the exposure way down, so that doesn't happen. No problem. Then you get this:

Hm, that's no good, is it?

You see, your eye is much better at scaling very disparate brightness levels in a single view in a way such that you can perceive the very dark parts and the very bright spots simultaneously. There's a technique that has been developed to try to manage something similar in photos, called high dynamic range (HDR) imaging.

What you do, is you take several photos of the same scene at different exposure levels, and then blend them together with software. You can do a cheap version of this, using only two images, with the iPhone app Pro HDR (may require a 3GS or later iPhone—I'm not sure about that).

Here's the combined image of the two raw images above, using the default settings in Pro HDR:

This actually shows the details better than the image at the top of this post (which is the result of tweaking those default settings a bit), but I think my tweaked image more accurately reflects how the scene looked to the human eye.

Not bad for a $1.99 app.

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