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iPhone HDR: A mini review and comparison

Yesterday Apple released the newest version of the operation system that powers the iPhone, iOS 4.1. This is mainly a big fix release, but there are a few new things, including the big surprise: HDR. As something of an HDR guy, I couldn’t be more thrilled to see it going mainstream like this. So as soon as I got a chance yesterday, I ran out and started testing it. What follows are my thoughts on iPhone HDR and some results.

First off, a brief explanation of HDR, and I’ll try to keep it as simple as possible.

What is HDR

HDR is basically a way to extend the dynamic range of a photo to match what our eyes actually see. Think of the dynamic range as the distance between the darkest dark and the brightest light. Now our eyes can see most of this range. The secret here is that our eyes are constantly adjusting to see both dark areas and light areas, but we don’t notice this and the perceived result is we can see a huge range of light. A photo doesn’t have this advantage of constant adjustment and so can only show us a small fraction of any given range of light. This is why, for instance, when you expose for the person in the foreground, you probably blow the sky (i.e., make it go pure white): The camera just couldn’t capture enough range of light to show you both the dark areas (the person in the foreground) and the light areas (the sky).

HDR seeks to correct this by extending the dynamic range of a photo. It does this by taking multiple exposures and combining them. So, for example, I take one photo where the person in the foreground is exposed perfectly (but the sky is blown), then I take another with the sky exposed perfectly (but the foreground is very dark). I then take the perfectly exposed sky and the perfectly exposed foreground and combine them into a new photo. (The actual process is a little more complicated, but this is the basic idea)

You might think of HDR as kind of a hack then to get more life-like photos. Now life-like is a very subjective thing, and you can process HDR in a way that makes it look very surreal. There’s nothing wrong with that (in fact, some of my photos on this site probably fit that description, though these days I tend to lean towards more realistic pictures), but you shouldn’t think those surreal images are the total of HDR. Think of HDR as basically a way of getting more light in photos.

Got it?

HDR on the iPhone! — iPhone HDR!

When you think about it, it makes perfect sense for the iPhone to add HDR. It’s much cheaper to add HDR than to produce camera sensors with more dynamic range. I expect more and more cameras of all price ranges will add HDR modes in the future. In fact, I strongly suspect we wil eventually see HDR becoming the default shooting mode, maybe even the only one.

Anyways, let’s get on with some photo comparisons.

For these comparisons, I included the regular non-HDR photo, the HDR photo, and an HDR photo from the Pro HDR app. I used auto mode in Pro HDR, by the way. You can get better results from manual mode, but I figure most people will use auto, so that is what I used for these test shots.

Comparison: non-HDR, (Apple) HDR, Pro HDR

(I’m only going to use smaller versions of the pics to save you bandwidth, but click on any to go to flicker and see a giant version if you want to compare in more detail)

This first one was taken early in the morning so we had a nice blue sky and good light.

compare3-house-sky

The HDR version is giving us more detail in the shadows, but overall it looks more faded. The Pro HDR version gives a more vivid image. A bit too saturated, but you can turn that down (I just used the defaults for this comparison, but a great feature of Pro HDR is you can make several adjustments on the photo before saving). You can see some slight haloing, but it’s not bad.

Next, a worm.

compare3-worms

Again, I think the regular is better than the HDR, but they are very close. The Pro HDR has more detail and better color, but… whoops, I moved the camera between shots. Pro HDR pauses a second between shots so it is very hard not to move. It tries to align shots, but sometimes fails. Here, also, the worm was moving itself, so Pro HDR (correctly) chose to align him instead of the ground.

Next, another closeup test: Some coffee:

compare3-coffee

Here finally we see a case where HDR is better than regular. It brings down the highlights nicely so everything is visible. A bit dark. The Pro HDR one here doesn’t bring the highlights down enough, although that does make for a brighter photo which many might prefer.

I was drinking that coffee in a large atrium area with light streaming in from everywhere. How about a snap of one of those well-lit walls:

compare3-hallway

The HDR gives more detail, so I’d go with it. Whoops, some ghosting, tho. Be careful when taking HDR — any movement between exposures will create ghosting. The Pro HDR in this case is a bit much, IMO. It gives you great detail in the shadows, but this ends up creating some nasty halos along the doorways. This could be avoided by shooting manual, but again I used auto for this comparison.

Now, how about looking towards a window:

compare3-lookingout

Hmm… it’s a toss up between the two HDR pics I think. The Regular shot doesn’t give us much: Most of the photo is too dark and the windows are blown completely. The HDR shot gives us more detail outside the window and brings up the shadows inside a hair. The Pro HDR version chooses to give us a better exposed room, but the windows are blown.

Let’s go back outside.

compare3-sky-contrast

The HDR gives more detail, but again looks faded, while the Pro HDR looks nice, except for those ugly halos. I’d probably pick Apple’s version here.

I decided to go towards the castle to test more. Here’s some stairs. The stairs are very dark and it’s very bright at the end, so you might expect this to be similar to the window situation.

compare3-stairs

And it is. The HDR version chooses to keep the shadowed foreground, but gives more detail in the highlights, while the Pro HDR version does the reverse, giving more detail in the shadows but less in the highlights.

Now, Okazaki Castle:

compare3-castle

Again, we see something very similar: Apple’s HDR keeps the shadows the same but gives more detail in the highlights, while Pro HDR gives more detail in the shadows but less in the… oh wait, it gets the highlights right this time. Definitely the best version in this case.

One more: How about sunsets?

compare3-sunsetotogawa

The HDR isn’t bad here, but Pro HDR has it beat again. Not ony does Pro HDR give us more detail in the sky, but gives us the foreground in a very nice way. There is lots of haloing here, but the sunset hides it well and you likely won’t notice it unless you look for it. I’d go with that one.

Although the regular version is very nice, and arguably the foreground isn’t very important here so having it go to black may be exactly what you want. Artistic choice.

Conclusion

As you can see, Apple’s implimentation of HDR is pretty conservative. At times you can barely notice it. Most of the time, I actualy prefer the original non-HDR image (or the Pro HDR image), but sometimes Apple’s version is nice.

The best thing about Apple’d HDR is how fast it is. The shutter release (you only hear one) is only slightly longer than for a non-HDR image, so they are taking these 3 exposures very quickly. This limits ghosting (movement between exposures) but more importantly, limits blur from moving the camera between exposures. Most people will handhold shots they take with their iPhones and so it’s very difficult to hold the camera still. This can be bad in any photo, but expecialy in an HDR photo, so any speed in taking them is a good thing. You can see the results of this above: There is very little bluring or ghosting in the Apple HDR images, whereas many of the Pro HDR images have some kind of motion blur due to me shaking the camera.

My final thoughts are if you are really into HDR, buy Pro HDR. It’s ony 2 bucks. Be careful about shaking between shots, use manual mode, and watch your saturation, but overall I think this gives the better photos. However, depending on the scene, you might sometimes use Apple’s buit-in HDR. At any rate, art is a very subjective game, so I leave final judgement to you on which is best.