Algorithms can’t solve everything, even those based on physics. Sometimes the blur is so bad that it can’t be removed, no matter the algorithm. Divide the resulting image by (1.0-mask weight) – 0.6 in the case of the example.Subtract the filtering image from the original image.(In the example below, the mask weight =0.4) Filter the blurred image using a “Mask Weight, which determines the strength of filtering.Obtain a Gaussian blurred image, by specifying a blur radius (in the example below the radius = 5).It subtracts a blurred copy of the image and rescales the image to obtain the same contrast of low frequency structures as in the input image. Here I am using the “Unsharp Mask” filter from ImageJ. It is by no means perfect, and is problematic in images where there is noise, as it tends to accentuate the noise, but it is simple. It is derived from analog photography, and basically works by subtracting a blurry version of the original image from the original image. The easiest technique for image sharpening, and the one most often found in software such as Photoshop is known as unsharp masking. Reducing blur, involves a concept known as image sharpening(which is different from removing motion blur, a much more challenging task). Here the object of interest is blurred, and the surround area is kept crisp. Here’s an example of motion-blur, a Montreal Metro subway car coming into a platform. Sometimes it would be nice to leave something in an image that inspires thought. We worry far too much about defining every single feature in an image, and too little on a bit of creativity. The results? I think they are just as good, if not better than if I had “stopped the motion”, or created a crisp photograph. I have been experimenting with adding blur to an image, either through the process of manually defocusing the lens, or by taking a picture of a moving object. But what about actually taking blurry images? Here blur was actually being introduced into an image. Then tilt-shift appeared, and was in vogue for a while (it’s still a very cool effect). It lead to the development of a variety of image sharpening algorithms to suppress the effect of blurring in an image. non-sharpness = blur).įor many years the concept of crisp, sharp images was paramount. Both the red and purple lines show objects not in the focal plane, creating large circles of confusion (i.e. The blue lines signify an object in focus. The further away, the more distinct the blur. The amount of blur depends on an objects distance from the focal plane. A photograph is exactly sharp only on the focal plane, with more or less blur around it. The following diagram illustrates the “ circle of confusion“. When in focus, the circle appears as a sharp point, otherwise the out-of-focus region appears as circle to the eye. Naturally the “circle” normally takes the shape of the aperture, because the light passes through it. Each of these points is reproduced by the lens as a circle. Light striking an object reflects off many points on the object, which are then redirected onto the sensor by the lens. In German the term used is “Unschärfekreis”, which translates to “ circle of non-sharpness“, which inherently makes more sense.Ī photograph is basically an accumulation of many points – which represent the exact points in the real scene. Although honestly – circle of confusion may not be the best term. CoC is also associated with the concept of Bokeh, which I will discuss in a later post. It is sometimes known as the disk of confusion, circle of indistinctness, blur circle, or blur spot. The CoC occurs when the light rays passing through the lens are not perfectly focused. But optical blur is by no means shapeless, and has a lot to do with a concept known as the circle of confusion (CoC). Another way is through manually focusing a lens.Įither way, the result is optical blur. It also means that objects not in the focus plane will be blurred. Opening up the aperture to f/2.8 allows in more light, and the camera will compensate with the appropriate shutter speed. Blur occurs when there is a shallow depth of field. One way is by means of using the Aperture Priority setting on a camera. This can be achieved in a couple of ways. When part of a scene is blurry, then we consider this to be out-of-focus. This is way easier than the manual focus that occurred in the ancient world of analog cameras. Most modern cameras automatically focus a scene before a photograph is acquired.
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