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Out-of-Focus Blur Tutorial – Circles of Light

Before we restore any images it is important to understand the concept demonstrated in this tutorial.


Blur Widths of an Edge in an Image

The image above shows profiles of an edge as it gets more blurred. At the top the edge changes straight from light gray to dark gray without any transition pixels, and that edge is completely "in focus". The second one has a transition zone of two pixels and therefore has a blur width of two. This is a very common blur width for today's digital cameras. As the blur width increases, it get progressively more difficult to determine where the blur starts and where it finishes.

The Blur Width is an important setting to reverse the blur of an out of focus image, and fortunately there is an accurate way of determining the blur width. The following image shows a picture of a lady which is progressively more out of focus.


It would be nearly impossible to determine the blur width by looking at the edge of her arm for example. The shiny bits on her sleeve, however, become circles of light with well defined edges. The diameter of the circle is the same as the blur width of an edge. It is quite easy to measure the diameter of these circles accurately.

So, as with motion blur, always start off looking for point sources to determine the correct settings for Focus Magic.

For an audio-visual presentation of this tutorial, click here.

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