I just posted a comment on another site that ended up being too long, so I thought I’d reprint it here for my own records.
Last week, Glyn Evans from iPhoneography.com put up a review of HDR Camera [iTunes link], a US$1.99 iPhone app that promised to magically turn single-exposure photos from a crappy 2-megapixel camera into HDR masterpieces. For that review, Glyn used one of his usual sample photos (a close-up of a bolt on a wooden gate) to demonstrate the app’s effects, but being the smartass that I am, I wrote in to essential say that I thought it wasn’t suited for the purpose at hand (scenes with potential for HDR photography are usually marked by a wide variance between their light and dark areas [hence the name, High Dynamic Range], such as landscape shots with lots of sky. Properly done, HDR photos show the world in ways that our eyes cannot perceive, with everything evenly lit despite an overpowering light source).
I recommended looking at another application that I use regularly, iFlashReady [iTunes link], which gives fantastic HDR-like results. Glyn agreed with my points, and took down his review for some rewriting. It’s just gone up again today, and his conclusion is still that HDR Camera is a waste of money.
My comment starts below. The remarks directed at another commenter, TrevorML, are in response to his question about the suitability of other general image editing apps on the iPhone to this sort of processing.
Since our correspondence, I’ve had the misfortune of being tempted to try HDR Camera out for myself, and have arrived at the same conclusions as you. It largely produces unpleasant results I would be ashamed to show anyone on my iPhone or Flickr account. Other apps like iFlashReady and PhotoFX are far more capable of taking a badly exposed photo (a fault of the iPhone’s limited camera software) and giving it some points of interest.
TrevorML: I’m glad you asked that question. Naturally it’s impossible for any iPhone app today to produce true HDR images, as those require a series of bracketed images as you have noted. The iPhone camera API does not allow apps or users to manually adjust the auto-exposure values, or any other values for that matter. The best we can have for the moment (perhaps iPhone OS 3.0 will hand over more control to apps) is apps that simulate the effect by recovering lost/hidden photographic data.
I initially thought that iFlashReady worked by simply boosting the brightness of photos, which is how we might normally approach the problem in Photoshop/Aperture/Lightroom, etc. but it’s actually more advanced. Looking at the developer’s website, I discovered that they produce a professional application, Essential HDR (www.imagingluminary.com), for Windows PCs. It seems that they’ve taken some of their technologies and applied it to iFlashReady, and probably decided that marketing it as a brightening app would be more commercially successful than proclaiming its HDR features. Rightly so, I think, as few mainstream iPhone users know or give a crap about HDR.
But iFlashReady does work as an HDR app in practice, and like I was saying, it goes beyond simple brightening. What seems to be happening is a localized contrast balancing that increases brightness in dark areas without touching already well-exposed spots. A dark object can be directly beside a bright one, and the effect does not bleed over. I think it’s probably more than just tweaking shadows and highlights too (as can be done in PhotoFX; I’ve tried and the results are not comparable), as it seems to have many subtle steps and a gentle tonal curve. The result looks surprisingly natural, and you can see that above. The ones from HDR Camera certainly do not.
Another thing that impressed me greatly was that the makers of iFlashReady seemed to have tuned their results with the iPhone’s camera in mind. Noise is effectively suppressed, or simply not exaggerated by their processing. HDR Camera’s “Night Mode” produces horrendous blotches of color noise across the entire photo. A few other apps I’ve seen also seem to just port their image effects over from the desktop side of things with no regard for imaging characteristics of the iPhone’s camera.
If I sound like I’m plugging the app because I know the guys who made it, well I don’t. I just use it nearly every other day and enjoy it a great deal. But since I’m recommending, another app I use often and find sadly underpublicized is the superb “ColorTaste with TOY LENS” [iTunes link] by Tandem Systems (who is really a rather friendly Japanese developer), which costs US$1.99. In my opinion, this app handily beats others like ToyCamera [iTunes] and Camerabag [iTunes] because of one feature: lens distortion modelling. It doesn’t just alter colors and add a vignette (although it can do those too), its Toy Lens mode subtly distorts and blurs photos to look like they came from a tiny plastic lens, like what you’d find on a Diana (120 film) or Vistaquest VQ1005 (keychain digital) camera.
Again, to tie it back to the earlier part of this comment, this sort of initiative in iPhone app development impresses me greatly. Rather than just doing a me-too image processor, these two companies have opened up new avenues of iPhone photography.