Blurring is a common artifact which occurs when technologies best suited for downsampling, such as interpolation, are used to upsample an image. Sclender can apply bi-linear filtering/blurring to an image before or after applying filtering to it. One particular strength of interpolation is its ability to stretch an image past its original aspect ratio while remaining recognizable, which is why Sclender uses it to stretch its output to fit your screen if "Fit to screen" is checked.