The Grumpy Editor's guide to HDR with Linux

Posted Mar 15, 2007 0:08 UTC (Thu) by dhess (guest, #7827) [Link]

My camera (a Sony DSC-V3) will do three-exposure bracketing. For HDR, though, I've found that it helps to have a wider range of exposures than the camera provides.

I'm no expert, but here's what I do for HDR shooting with a Nikon D200.

The D200 has an exposure autobracketing feature which supports, among other, less useful things, 3-, 5-, 7- or 9-exposure brackets. In this mode, the largest exposure increment that the camera provides is +/- 1 stop, so you can capture at most 9 stops of range in a single exposure autobracket. When I want to capture an HDR sequence, I use the feature to take either 5 or 9 exposures with a +/- 1 stop exposure increment. In my experience, 3 exposures at -1, 0 and +1EV are too few to get good HDR results.

I use 5 exposures for quick-and-dirty shots in daylight when the subject matter isn't worth breaking out a tripod, but there's some nice light, and the final image will benefit from a little extra dynamic range. I take these shots by hand, but I've learned to remain pretty still, and the results are usually decent. If there's too much shake, I've still got at least 3 exposures to choose from as an LDR image (sometimes the +1 and/or +2 exposures are too blurry to be considered). This approach doesn't work too well for nighttime shooting :)

I use 9 exposures for "money shots." I almost always use a tripod for these sequences. Sometimes, e.g., for strong daylight scenes or well-lit nighttime scenes, I'd prefer to go beyond +/- 4EV, but that's as far as I can go with the D200's autobracketing feature. I'm not patient enough to shoot, adjust the exposure manually and repeat, nor am I skilled enough to keep the camera from moving while I'm adjusting the controls, even on a tripod. I recently bought a Nikon MC-36 remote control for the D200 under the assumption that I could adjust the exposure from the remote, but it doesn't work in a way that's useful for HDR shooting: for some bizarre reason, the MC-36's exposure time resolution is in whole seconds! I guess I could try building my own. I haven't done any research about the 10-pin remote connector on the D200, but I'd be surprised if Nikon publishes any information about the protocol. Maybe it's time to start a GNU movement for digital cameras.

What would be nice is if the camera could do the entire HDR technique internally, giving a raw file with the full range.

Don't hold your breath. The OpenEXR team has tried on numerous occasions to engage various camera vendors about supporting HDRI, but each time we've gotten nowhere. We're small and pretty niche, so we're easy to ignore -- no real surprise there -- but I've heard that Adobe and even Microsoft have trouble penetrating the monolithic corporate giants that are the major camera manufacturers. It's hard to know where to begin talking to them about the idea.

I think it's going to be a slow road. With the exception of Foveon and their X3 CMOS device, which hasn't gained any traction in the market, nobody appears to care about LDR color quality, let alone HDR. Unfortunately, the current trend amongst camera manufacturers is completely focused on more megapixels. More pixels means more heat and longer read-out times. More heat means more noise, i.e., lower color fidelity, especially with long exposures. Longer read-out times means fewer exposures in a given amount of time, which increases the chances of camera shake or moving subject material. We're going the wrong direction.

But articles like this one help by getting the word out! I hope that most people, once introduced to HDR, would agree that it makes a bigger difference in photo quality than more pixels, in today's post-10 megapixel world, anyway. Getting "pro-sumers" to clamor for it is the fastest way to getting HDR support in our cameras.