Science in the System: Blur Effects, Part 1
Blurry vision and blur effects in photography
In this multi-part series, I provide clarity around blur, from vision to photography to effects in app and game design.
When my sister was 10, she convinced herself there was something wrong with her eyesight. She decided she was nearsighted.
I was skeptical. I had no idea how being nearsighted might benefit her, but I suspected there was some sort of angle — perhaps she found a way to get out of math class.
Eventually, my mother did what any parent living in a rural area of Arkansas would do: she took us to the closest Walmart to get our eyes checked. My vision was fine, or so I thought, but there was a two-kids-for-price-of-one discount, so I hopped in the truck and we drove half-an-hour to the Walmart in Hot Springs.
Two eye exams later, it turned out that my sister was correct: she was nearsighted, with 20/50 vision. To our surprise, I was also nearsighted, with the exact same prescription.
On the discount frames rack, I selected the least hideous pair of frames I could find and waited an hour for the technicians to install my lenses. And then I experienced corrected vision for the first time.
Texture!
The amount of information in the world tripled and my eyes were bathed in a sea of detail: the green blanket that had been the ground transformed into individual blades of grass and I could see each of the sharp shadows they cast in the midday sun. The billowing green and yellow tops of trees changed into collections of branches and leaves. The smooth brown cylinders that supported them grew a covering of natural, rough shingles. My eyes could almost feel the bark’s textured edges.
That first day, I must have spent hours taking in all the textures I could find.
And then I barely wore the glasses again, because I hated the weight of them on my face and they looked horrible on me. It wasn’t until a year later when I turned 13 that I would experience all the glorious textures of the world full-time thanks to the weightless freedom contacts provided.
What causes blurry vision?
Human vision is a complicated negotiation between physical components — our eyes — and some seriously hard-core post-processing. In my case, my vision was blurry because of an issue with a physical component.
In an eye with 20/20 vision, the lens focuses the image on the retina:
In a nearsighted eye, the eye is too long or the cornea is too steeply curved, which causes the lens to focus the image on a point in front of the retina:
The result is that nearby objects look sharp, but things get blurry as they get farther away. Glasses (or contacts) fix the issue by refocusing light on the proper point, the back of the retina.
About 42 percent of Americans between the ages of 12–54 are nearsighted.
What causes myopia? According to the National Eye Institute, there are genetic factors that increase your chance to develop nearsightedness. But there appear to be other factors, too: one long-term study shows that children who spent more time outdoors have less of a chance of developing nearsightedness.
I mentioned that your brain does some pretty amazing post-processing of the images it receives from your eyes. Did you know that your brain can trick you into improving your vision? (Temporarily, at least.) In one experiment, patients looked at an optical illusion and then took an eye test… and were able to read finer print than normal, because the optical illusion caused their brains to temporarily magnify their vision. You can read about it here.
Sometimes a little blur is a good thing
While blurry vision isn’t ideal, blur effects can enhance photography, video games, and app design.
Blur effects in photography
There are two types of blur effects in photography: motion blur and focus blur. Motion blur occurs when the subject (or camera) is moving fast enough and the shutter speed is slow enough that the camera sensor captures its movement, creating a motion trail.
In this example, I created a motion blur by twisting my camera as I took the picture:
You can eliminate motion blur by increasing your shutter speed to take a faster photo. A dog running across the yard will be blurry with an exposure of 1/15 of a second, but sharp at 1/2000 of a second.
Photographers use motion blur to convey a sense of action and speed.
When photographing water features, such as waterfalls, you can use a slow shutter speed to give the water a smooth, glassy look.
The other type of blur, focus blur, is a little more complicated. Explaining it requires taking a look at the mechanics of the camera lens.
A camera lens has a diaphragm that controls the amount of light the camera sensor receives. This diaphragm also influences how much of the image is in focus. We describe the size of the opening as the lens’s aperture, and we use f-stop numbers to describe its size. Larger f-stop numbers indicate a small aperture, and smaller numbers indicate a larger aperture.
A small opening, such as f/16, lets in less light, but increases the depth-of-field of the image: the portion of the scene that’s in focus. A larger aperture, such as f/1.4, lets in more light, but it decreases the depth of field, so less of the scene is in focus.
Lenses that have larger apertures are typically larger, heavier, and more expensive than lenses with smaller maximum apertures.
This series of images shows how different apertures sizes determine how much of the image is in focus.
In most photography, you actually want part of the image to be blurry (“defocused”). Blurring the background of a portrait helps the subject stand out, and the blur effect itself can be beautiful. Photographers call the out-of-focus blur effect “bokeh.”
One of the exceptions is landscape photography: most landscape photographers prefer images that are sharp from corner to corner. One way to achieve this effect is to use a small aperture, such as f16 or higher. Another way is to use a technique called focus stacking, where you take multiple photographs of the same scene with different elements in focus, then stitch together the sharpest parts in a photo-editing program. The end result is a composite photograph that’s sharper than any lens could take with a single exposure.
Blur effects in photo-editing
From enhancing the color of a sunset to removing your ex from an otherwise awesome photograph, image editing applications, such as Adobe Photoshop, let you do some amazing things. One of those things is creating an artificial blur. Artificial blurs have a lot of uses:
- Hiding dirt or wrinkles in a photographic backdrop
- Removing dust and noise
- De-emphasizing elements so the subject stands out
- Smoothing skin or evening skin tone in a portrait
Most photo editing applications provides a variety of blur effects. Let’s take this image of Smoky the cat and try a few of them out.
- A Gaussian blur (named after mathematician and scientist Carl Friedrich Gauss) creates a smooth, hazy effect.
- A box blur blurs an image based on the average color value of neighboring pixels. (A box blur is sometimes used to simulate the bokeh effect of camera lenses.)
- A radial blur simulates what an image might look like if it were spinning quickly.
Some applications, such as Adobe Photoshop, provide more sophisticated blurs like surface blurs, motion blurs, and blurs that try to simulate the bokeh of a lens.
Certain phones, such as the Google Pixel 2 and the Apple iPhone X, can automatically apply a digital blur as you a take a portrait, in an attempt to simulate the shallow depth-of-field and bokeh of a lens.
While photo-editing blur effects are very useful for a lot of tasks, it’s difficult to get them to simulate the look of a defocused background with nice bokeh produced by a good lens with a large aperture. Part of the reason is that the background blur is produced by lens mechanics operating on part of the background that’s blocked by the subject. To accurately simulate a background blur, you need information about a part of the background that wasn’t directly captured in the image.
Up next in part 2
In this article, we took a brief look at my life as a nearsighted tween and learned a bit about how to create blur effects in photography. In my next article, I’ll talk more about computer-generated blur effects and their applications.
References
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