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The magic (image resampling) kernel

The Magic Kernel

As a consequence of these properties, by mid-2013 we were able to deploy Magic Kernel Sharp to the back-end resizing of images on Facebook—with not only better quality, but also greater CPU and storage efficiency, than the code stack it replaced. The IJG library used that method by default, but it also provided an optional mode called “fancy upsampling.” The following example (shown at twice real size, with each pixel nearest-neighbor-upsampled into a 2 x 2 tile, to make it easier to discern details visually) shows the difference in the resulting reconstructions (note, particularly, the edges between red and black): (Note that, as described in the introduction above, all of these images are more blurred than they need to be; this is related to the required post-sharpening step in Magic Kernel Sharp, whose discovery was at this point in time still seven years in the future, and which will be discussed shortly.)

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