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After scanning a picture into a black-and-white image, the process often produces a dithering pattern to represent half-toning of gray scale between extreem black and white.
With sufficient resolution of scanned image (300 or 400 DPI), it is possible to restore the gray scale image using different filters when resizing the image 50%. Choice of filter determines both amount of smoothness or level of detail, and the resulting compressed image size (gray scale PNG is best).
Here are the sizes produced by different filters using the XnView program.
169,221 IdeaPad_Bspline.png 178,206 IdeaPad_Bell.png 181,418 IdeaPad_Gauss.png 192,934 IdeaPad_Hanning.png 196,601 IdeaPad_Mitchell.png 304,498 IdeaPad_Hermite.png
Below are samples of the same results with sizes of the cropped thumbnails. Notice the details. Depending on purpose of the image, different choice is preferred.
