28 September, 2010

HDR on the iPhone 4

The nice thing about the iPhone camera is the large amount of software available for it. I've seen time-lapse/stop-motion apps, here is a HDR app, next I'll be writing about a 3D app and maybe after that I'll get an app for light painting. Ordinarily, this software would be useless if the camera were only 2 megapixels, but now that the camera has been updated to a very capable 5 MP autofocus camera, the iPhone camera has functions not available on dedicated cameras.

One of the new features in iOS 4.1 is HDR photos. Normal photos may include some very bright and very dark areas (e.g. taken inside a house looking out), so it's difficult to expose the entire photo correctly. HDR (High Dynamics Range) takes a few photos at different exposures and picks the best exposed areas from all photos to combine them into a properly exposed photo.

When I first heard about HDR in iOS 4.1, I searched for a HDR app and found Pro HDR by eyeApps LLC (AUD$2.49).
It has auto or manual mode, and seems to be able to use photos from your library (I haven't tried this). At first I thought manual mode would be very complicated, asking you to decide on exposures, white balances and which regions to use from which image, then I found all it wanted was the lightest and darkest parts of the image. I think this additional control makes it better than auto mode.
  • Manual mode
  • Adjust white balance, contrast, saturation etc. in the finished photo
  • Automatically aligns photos
Manual mode
Auto mode
This scene isn't the best for testing HDR photos, but it shows that manual mode gives better exposure, especially under the table in the picture.

iPhone 4 camera, no HDR
Both HDR pictures are clearly better than without HDR. Overdoing HDR can result in unnatural pictures, but this looks ok.

One of the disadvantages of HDR is that it's very slow. For Pro HDR, you have to take 2 pictures (auto mode is even slower as it scans through all exposures before taking them), and it spends even more time processing the photos. HDR in the camera app takes pictures much faster, but spends just as long processing them. I recommend leaving HDR off in case you want to take a picture in a hurry.
iPhone 4's HDR
The iPhone claims it takes 3 images for HDR and merges them, but I suspect this as it starts processing very fast, before it could have taken 3 pictures. You can save the pre-HDR photos too, which looked just like the one without HDR above.

Is it worth buying an extra HDR app? I say if you use HDR, yes. The manual control is very useful, and you can be sure this app is performing true HDR. HDR comes in useful when taking pictures outdoors and the sun is behind your subject.

More HDR photos:
Taken using Pro HDR, I think with auto mode

Taken using Pro HDR, I think with auto mode. Note how the tree leaves in the top right don't align properly.

I think this was using HDR on the camera app, with and without HDR.

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