IPhone HDR Extremes
September 22nd, 2010, 3:41pm by KelvinDid some testing of the new iPhone 4’s HDR capabilities today at the Apple Store. Here’s what I found– It’s real HDR and it’s useful in certain (high contrast) circumstances. Since the iPhone saves both versions (standard exposure and an HDR), it’s certainly nice to have the option, as Joanie noted. Click through for the comparison shots.
I chose a high contrast scene for my testing that is a challenge to properly expose. First shot is spot-exposed for the exterior of the store. Note that the interior is pretty much in full silhouette in the standard shot.
Here’s the HDR version of the same scene. The exterior is represented by less of the dynamic range (compressed), but now, you can make out the interior (the Apple store patrons).
Now I move to the opposite extreme, and spot meter on the woman. Consequently, the exterior is now overexposed. Not only that, but the blown out background bleeds onto the foreground. Sometimes, this is a desired effect, but in this case, I find it kinda ugly (and may indicate a dirty lens).
Finally, the HDR version of the previous shot (exposed for the woman). Background issues are now resolved, everything is exposed within the range of the image.
The verdict? Depends on what your subject is. If I wanted to take a photo of the woman, I would probably want to use my whole dynamic range on her, even if it meant the background was completely white. I actually find her underexposed in all these shots, but more so in shot 4 than in shot 3 because of the tradeoffs in the HDR processing. There may be other scenes though where you do want detail in the whole image, and HDR might be the only way. Nice option, certainly.
As for sharpness, I don’t really notice any effect from the HDR. If it’s really a combination of 2 or 3 different exposed photos, there should be some camera shake effects. Either the software is doing a great job compensating, or the camera actually shoots in RAW :).
September 22nd, 2010 at 4:20 pm
I take back my statement about seemless overlaying– there’s evidence of misalignment in the salesperson’s hand in the HDR version (shot 4). So it’s at least 2 separate photos– still pretty impressive that the overlaying is as successful as it is. There must be at least half a second separating successive shots– way too long to assume the hand is steady enough. I wonder if the gyroscope is involved somehow in the reconstruction, similar to how image stabilization works (but not real time).
September 23rd, 2010 at 3:23 am
Dang. Comment didn’t post earlier.
What I tapped out on the Pre was this… I’m almost certain that the images are lined up simply by lining up the images. Slide pixels to minimize the differences between pics. You’ll get some ghosting from movement, but no camera shake affect.
So is that the same store we did our earlier iPhone 4 photo tests?
September 23rd, 2010 at 10:02 am
The iphone would have to both translate AND rotate the 2 or 3 images, right? Is it trivial to line them up? I would have thought that to be too processor intensive for the phone, especially since the HDR-processed version is available nearly instantly. Seems to me that accessing the gyroscope log for guidance would be easier, assuming it had the sensitivity necessary.
September 23rd, 2010 at 2:02 pm
Image alignment isn’t too bad if they have an optimized FFT algorithm. The algorithm is actually quite trivial.
September 23rd, 2010 at 3:21 pm
That’s good knowledge, Lance. There are a couple of HDR apps in the App Store which make use of on-phone image alignment, so I guess it can’t be that hard. Here’s a comparison of TrueHDR vs ProHDR. ProHDR seems like it’s probably worth the $2.
http://chris.pirillo.com/hdr-iphone-camera-test-true-hdr-vs-pro-hdr/
September 23rd, 2010 at 3:27 pm
had to fish that last comment out of the spam filter. Any idea what the spam profile is?
September 23rd, 2010 at 5:58 pm
Here’s another review from Flickr friend & wedding photography superstar Ryan Brenizer. Back in April, before Apple invented HDR.
http://www.enduserblog.com/2010/04/get-more-lattitude-out-of-iphone-3gs-photos.html
September 23rd, 2010 at 9:00 pm
Interesting. He came to the opposite conclusion. Well, it’s nice to have options, I guess.