Turn Your iPhone 4 into a Magnifying Glass

The camera in the iPhone 4 is very basic, but can be used as a modest magnifier with 5x zoom. However, there are applications that can take you beyond the basic camera with features like rotation, constant LED illumination, higher magnification and image stabilization. Here’s some background on image enlargement and a rundown of the best magnifiers we’ve found.

There are many, many magnifying glass applications available for the iPhone 3GS, 4, and now the iPad 2. However, the features vary widely and not all of them are better than just using the 5x zoom feature of the built in iOS camera. However, there are a few that are terrific and worth having as a supplement.

I got interested in this subject when I was watching the March 28 (2011) episode of Castle on ABC. Richard Castle, who, regrettably, has had his Apple iPhone replaced by what appears to be an LG Quantum, uses a magnifying glass app to inspect a photo and break open a case. Intrigued, I started investigating the various magnifying glass apps for my iPhone 4 and compared them to the basic features of the built-in camera.

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Richard Castle’s smartphone and magnification app (Credit: ABC)

A Basic Digital Image Problem

Before I talk about the apps, I need to mention a basic optics problem related to these magnifiers. Many of the magnifying glass apps in the App Store are criticized and given poor reviews because the users aren’t aware of a fundamental problem of digital camera optics when it comes to enlargement.

I’ll let Don Edrington explain it:

Let’s assume that the original photo is a sunset with vibrant shades of yellow, orange and red. Then let’s zoom in on one of the tiny yellow squares, which is probably surrounded by squares in varying shades of yellow-orange. Well, if you ask your image-editing program to double the size of this picture, it will actually come out four times larger (double the height by double the width). This means that the number of tiny squares will need to be quadrupled.

Well, when all these new squares are added in, how does your computer know what color to make each one? [Emphasis mine. -JM] Take the aforementioned yellow square, for instance. It needs to be supplemented by three new squares; and the most logical thing to do is make them all yellow.

Now, where you had one yellow square surrounded by others of various yellow-orange hues, you have a block of four yellow squares surrounded by blocks of yellow-orange shades, which are also four times larger than they were originally. These blocks are what make the enlargement look blocky.”

Something that may contribute to this misunderstanding is a visual trick played on TV and in movies. We’ve often seen police trying to get a licence plate from a surveillance photo, and we typically see a technician blow up a licence plate so it can be read. Amazingly, the digital photo gets a hundred times bigger and the resolution is maintained. The plate is easily read. That’s blatant cinematic trickery.

That’s not what happens in real life. The photo only has so much inherent resolution, that is, licence place inches (or cm.) per pixel. Blowing the pixels up doesn’t make the picture clearer, it makes it much blockier, and much worse.

Here’s an example image from a tutorial I found to illustrate the blockiness upon enlargement.

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Digital enlargement leads to blockiness

Now that’s not to say we can’t attack the problem with some cool mathematical algorithms. Without going into much detail, there are filters than can improve the appearance of the image via interpolation, such as Bicubic smoothing, and Genuine Fractals to name two. These algorithms make the photo look less blocky because they try to be smart about how to add those extra pixels described above by Mr. Edrington. Here’s a tutorial on the problem and how some of the algorithms work. However, these algorithms still can’t add resolution that wasn’t in the original image, they just smooth out the appearance.

Once you understand all all that, you’re ready to start blowing up some images.

Criteria for Magnifying Glass Apps

The iPhone 4 has a built-in camera app. If you focus on an object, then touch the screen, a slider will come up (shown in the red circle below) that allows you to zoom the image up to 5x. This can be used as a rudimentary magnifying glass, assuming you have good lighting.


Basic iPhone zooming, up to 5x

However, there are limits to what you can do here. All you can do is snap the photo and let the flash and HDR settings take effect. But, for example, you can’t force the LED to come on for better illumination as you inspect the item of interest in real-time. The magnification is limited to 5x. So what one really needs is a dedicated magnifying glass app that does a a better job than simply using the built-in camera app as a stop gap.

Confronted with a myriad of magnifying glass apps in the Apple App Store, I started making a list of features that I think are good to have.

  • Greater than 5x zoom
  • Ability to turn on the LED flash for better illumination
  • Save enlarged image to camera roll
  • Rotate the image
  • Stabilize the image

Amazingly, not every magnifying glass app has all of these features. However, I did find a few that have many or most of the features.

mag-4Magnifying Glass (US$0.99)


mag 6aMagnifyer (US$1.99)

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mag 5aMagnifier TiAu (US$0.99)

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mag7aOver 40 (Free, iAd supported)

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Here’s a chart of how these four apps compare.

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Just as with binoculars, higher magnifications are hindered by the inherent jitter produced by hand holding the iPhone. For really large magnifications, above about 7 to 10x, you’ll need some kind of support. Also, only two of the apps, Magnifier (TiAu) and Over 40, provide a visual indicator on the display of the numeric magnification. That may be important to some users for technical reasons. Finally note that extended use of the LED flash for illumination will rapidly drain your battery.

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Maximum magnification has uses and limits (via Magnifying Glass app)

Buying Advice

The Magnifying Glass app by Jeff Hanel has a definite retro look to it, but it’s the most full-featured. It can rotate the image, save to the camera roll, turn on the LED, and tries to stabilize the image as best as it can using the iPhone’s accelerometer. It includes a contrast filter, but I didn’t test that. Zooming, with the + and - buttons is smooth. For the money, this is the best choice.

Magnifier (TiAu) from TiAu Engineering UG is my second favorite. It can e-mail the photo on the spot and shows the magnification in the slider. The control panel at the botom slides out of the way for better viewing. My only complaint is that the buttons and the slider are too close together for me, and I would constantly activate items unintentionally.

Magnifyer from Alibali Software has a great user interface — just swipe to enlarge. It has a cool a sound effect, but it can be disabled. You can inspect your camera roll from within the app. There’s an auto magnify mode that works by just moving the iPhone in and out. Unlike all the other apps, you can add a caption to the photo. Unfortunately, you can’t turn on the LED for extra illumination, and it’s the most expensive of the four. It comes in third.

The Over 40 app from TLA Investments is really just designed as an instant magnifying glass. It can’t save your image to the camera roll, and isn’t really well thought out because it doesn’t focus on the right features. But it’s free thanks to the iAd strip along the bottom. If you really want a nice magnifying glass without distractions, the top two here are a better selection.

As I noted above, I tried to pick candidate apps that met my criteria, but also apps that got high marks from the users. Unfortunately, in some cases, some of these apps got very low ratings because many of the users were unjustifiably disappointed by the clarity of the enlarged image. Perhaps they had false expectations based on the cinematic trick I described above. So I picked the ones with the best features and tried them out myself. They all worked fine and I didn’t have any problems with crashes.

Also, I don’t know if any of the apps used any of the special interpolation algorithms described above. The upshot is that these are not scientific apps or high level photographic applications. If you’re trying to inspect the fine print on a prescription label or some of Apple’s iPod docs or the fine print of a contact, then save to the camera roll, then the top three apps here will do the job nicely. Just be aware that high magnifications will need some physical support, and there’s no way to avoid blurriness in the enlarged image. Your own testing and experimentation will be the best guide. Maybe you could even solve a crime like Richard Castle. Well … maybe that’s asking too much. Dead bugs?