HDR Images

One of the only kinds of "Photoshop" manipulation I enjoy using is the creation of HDR, or high dynamic range, images. It's a powerful tool, photographers used to rely on split neutral density filters, sort of like sunglasses for the camera, split, so the top half of the picture would be darkened (the bright sky) and the bottom half would be exposed as normal. The reasons for this become obvious on a day like today:



In this example you can see that there was a LOT of contrast, the sky is very bright, so the camera had to pick an exposure that wouldn't be too bright. At the same time, the foreground is dark, and the camera wants to brighten it up. Unfortunately, it's forced to pick something in between, so we get a sky that's a bit too bright, and a foreground that's too dark.

The way we get around this is to take 3 pictures instead of one:



We shoot the first way too bright, in this case 2 f/stops higher than the camera would have picked. The foreground is bright, but the sky is hopelessly washed out. The middle picture is the same as earlier, not quite right, but the midtones are good. The last picture is 2 f/stops darker than metered, but the sky looks just about right.

The real wizardry starts now. In order to get the best from each photo, we turn to software to generate a 32-bit HDR image. I'm not going to get into it here, but this is not the same 32-bit colour your display drivers will tell you you're looking at. Trying to cram this much information into a picture stresses my poor old laptop a great deal, and the poor attempt that a 32-bit monitor makes comes out looking like this:



Obviously we're not done yet. The last step is to use whatever software we've chosen (Photomatix, in my case) and find a way to use this wealth of colour information. This is more about taste in pictures than anything else, no need to be an imaging specialist, I like my final result about like so: