The many definitions of blur

Over the years I’ve been developing Blurity, one thing has become clear: not everybody thinks of “blur” the same way.

For me, and thus for Blurity, a “blurry” image is one that has had its high-frequency content obscured through either motion or poor focus. Other than that blur, the image is fine: correctly exposed, minimal noise, and an acceptable resolution. This idea of a blurry image is common to many Blurity customers, particularly those with photography experience. Others have an entirely different view.

Through email exchanges with customers and potential customers, I’ve learned that many people consider “blur” to include image degradation of all types. Sometimes, the problem is excessive noise, whether from the sensor, from quantization, or from compression. Other times, the blur is nominally motion blur, but the image is so horribly over-exposed that all of the latent information has been lost.

When the image is noisy, what you really need is a good noise-removal program. The latest versions of Lightroom, Photoshop, and GIMP all have decent noise-removal tools.  My favorite is a third-party tool called Noiseware.

If the image is over- or under-exposed, again Lightroom, Photoshop, or GIMP are all your friends. It might not be possible to restore the areas that have clipped to white or black, but generally a decent amount of improvement is possible.

But those situations are relatively infrequent. By far the most common misconception of “blur” has to do with low-resolution images.

The exchange usually starts as a complaint. “It isn’t working!” the person will say about Blurity. I ask them to send me a photo, and what I get is a thumbnail-size, highly compressed hint of an image. Further communication reveals that the person was expecting Blurity to enlarge the photo, leaving behind something high enough resolution to print large.

If you want to enlarge this…

Blurity doesn’t do that. Nothing does that. It isn’t that Blurity doesn’t know how to scale up an image using something like bicubic interpolation (though some people seem to think that feeding in such an image will magically work better than the original thumbnail). The problem is that increasing the resolution of an image is only distantly related to deblurring an image, and even then, there are practical limits to how much extra detail can be recreated.

…don’t expect much better than this

When Blurity deblurs an image, most of the newly revealed detail was already in the image; it was just hidden. Blind deblurring, which is what Blurity does, is what’s known as an ill-posed inverse problem, meaning that some assumptions are necessary to make the deblurring work, but they are relatively minor.

On the other hand, increasing the resolution of an image, a task called “super resolution,” requires many more assumptions about the nature of the enlarged image. There is a lot less data to work with than in the blurry-image case.

As I’ve mentioned before when writing about enlarging small images, there are a handful of utilities that can help slightly increase the resolution of photos. Results tend to be hit-or-miss, but it’s worth giving them a shot. Just don’t expect Blurity to do super-resolution.

Actually, there’s one more common support email type: the person with the severely out-of-focus image. Although the Blurity user manual makes it very clear that only small focus blurs can be repaired, I still get a number of emails from people who accidentally turned off autofocus on their DSLR or had their cell phone camera decide to focus on the mountains in the background instead of the people in the foreground. Oftentimes, the unfocused images are of loved ones, handshakes with the famous, or cherished vacation souvenirs.

Generally, Blurity can recover a decent amount of detail in an out-of-focus image. The problem is that the photos tend to be so out of focus that there are large gaps in the information that’s left. Those gaps lead to visual artifacts, like ringing (discussed near the end of the user manual). While ringing isn’t a problem for forensic work, it’s highly noticeable on peoples’ faces. That makes people unsatisfied.

So what to do about that? First, understand that Blurity is best used on either motion blur or relatively small focus blur. If plenty of detail gets revealed during the deblurring, but some visual artifacts are left over, those artifacts can sometimes be smoothed over manually with a photo retouching tool like Photoshop.

Just remember, have reasonable expectations, prepare for some artifacts, and don’t expect tiny images to magically become big.


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