On HDR photography with the smartphone

By | 1. November 2012

Nature confronts us with scenes of high contrast, for example the sun shining through a tree. Human eyes can deal with this much better than artificial cameras: when looking through the tree, we may still see that the sky is blue and contains clouds, and that the leaves are green, while a camera might only see black silhouettes against a blindingly white sky. That’s because the human eye has a higher “dynamic range” than a typical camera. One way to address this problem, in a limited way, is a very good (and expensive) camera. But there is another, cheap way for smartphones: get an app that takes several shots of the same scene with different exposure times, and computes a final, improved image using the combined information from all those shots. A tried this with my Android smartphone, a Samsung Galaxy Nexus, using the app “HDR Camera+”. First, I took the following shot without HDR, a forest track when the sunlight came from the front and was reflected off the ground. In the darkest patches of the image, we can hardly see the leaves, and in the brighest patches the reflection is so strong that we cannot see any structure:

Without HDR

Next, I took a shot of the same scene with HDR Camera+. Note how well we can see the leaves in the darkest patches now, and that we can also see more structure in the brightest patches. The HDR image is very close to what my eyes actually saw. (They saw a bit more detail still.) So HDR clearly brought an increase in realism.

With HDR Camera+

Strangely enough, one might still consider the first, more unrealistic shot to be the better one, because the exaggerated contrast has an artistic, film-noir feel to it. But that was involuntary, so it can hardly count as a reason to stay away from HDR.

Of course, even from a technical point of view, the HDR shot is far from perfect: the bright patches in particular look slightly artificial. I needed a dozen or so experiments, each consisting of shooting some scene with and without HDR, to get a feel for the strengths and limitations of the method. Considering the low price of the app, I can easily recommend to give it a try.

6 thoughts on “On HDR photography with the smartphone

  1. mkl

    What is it that you see when you are in the forest in this situation? Is it not that the impression of the scene in your head is composed of tens to hundreds of different instantaneous impressions that your eyes make with differently wide opened iris?

    What is a good photo anyway? Is it what the camera saw at that instant? Is it what a single impression of your eyes saw? Or is it what the whole apparatus of your human senses pieced together for you? The actual, quantitative difference between bright and dark was as in the first picture, so the second is not a scientific measurement. What is reality?

    Also, the reason that the highlights are blown while the shadows are underexposed is because the exposure metering of your camera tries to find some middle ground between over- and underexposed areas in the picture. If your photo app supports this, try locking the exposure while pointing into the dark forest, then recompose and shoot: the leaves are green while the highlights are still (and even more) overexposed. Or do it the other way around to get visible structure in the sky against a black forest.

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  2. Carsten Führmann Post author

    Markus is that you? Anyway, when you ask what I see in the forest, you are getting into an interesting but difficult territory. In particular, once we’ve started asking such a question, we might go further and ask: is it desirable at all to capture what one sees? That is, do I want my foto to be realistic? If the answer where an unconditional “Yes”, then I’d probably have switch to 3D movies… Now that I think about it, I guess what I wanted here is be able to make *one* image that looses as little dynamic range as possible. You are right though that one could have different goals, e.g. under- or overexposing areas to emphasize certain parts.

    By the way, this post of mine is beginning to age, since more modern Android phones have a better HDR built straight into Google’s camera software.

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  3. mkl

    mkl? yup, that’s me 🙂 I started with photograpy a few months ago, so now I’m all interested in these kinda things. http://lambdanaut.net/

    By the way, sometimes there is still enough information in the highlights of a single image, and you can recover it by creating a copy, tuning brightness of the copy and then blend together with the original using a gradient mask. That’s what I did on those to recover the sky:
    https://secure.flickr.com/photos/dermkl/13702766803/
    https://secure.flickr.com/photos/dermkl/13228100265/

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  4. Carsten Führmann Post author

    Hi, I belatedly checked out you blog. Nice! (1) “Lambdanaut” is a pretty cool URL, (2) some really nice pictures, not least the startrails, (3) the flash bouncer is cool. In the past, I could never “save” an overexposed sky , you probably have a better camera or better method. To be honest, I’m not ambitious as a photographer. I guess what fascinates me most is how software can compensate for lacking hardware.

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    1. Carsten Führmann Post author

      Hi, thanks for the thoughts! I guess one should distinguish two things: on the one hand, the poor implementation of HDR on my ex-smartphone. (My new Nexus 5 does it better.) And on the other hand, the fact that multiple exposure *can* capture more information, when done well. An extreme example is astronomical photography, where e.g. a galaxy is captured at several wavelengths, and the superimposed false-color images are presented. I guess it should be possible to build an every-day camera whose dynamic range is closer to that of humans. I guess such cameras already exist. But I haven’t checked.

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