File:Kcc rescale 03a Gimp bicubic interpolation.jpg

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Kcc_rescale_03a_Gimp_bicubic_interpolation.jpg (557 × 425 pixels, file size: 169 KB, MIME type: image/jpeg)

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English: Part of a series of images to compare and contrast the levels of spatial aliasing that can result when an image that contains some strong spatial frequencies is digitally rescaled. An image of an 1801 engraving of King's College Chapel, Cambridge was used as a test object, and resized to 50% using different filters and different programs.

The image on this page was resized to 50% using GIMP 2.6.12 with the "bicubic interpolation" option -- i.e. taking into account nearby pixels using a bicubic filter. The result produced seems essentially identical to that obtained in the Image Magick "box filtered" image. Compared to simple decimation, the unwanted Moiré patterns are much reduced, and are essentially no longer visible in the road and the building and the clouds. However, although softened a bit, they do still remain in the sky.

Identical results to a box filter are not, on the face of it, what one would expect; so it could be that what GIMP 2.6.12 is actually implementing here may be different to what it is advertising.

Other images in the series look at the results of using various available lowpass filters to try to further minimse or suppress such artefacts.
Date
Source This file was derived from: F. Roffe after P. Nash (1801) - King's College Chapel - sanders13001.jpg
an engraving first published in 1801.
Author John Roffe (1769-1850), engraver, after Frederick Nash (1782–1856)
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This is a faithful photographic reproduction of a two-dimensional, public domain work of art. The work of art itself is in the public domain for the following reason:
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current19:08, 6 March 2012Thumbnail for version as of 19:08, 6 March 2012557 × 425 (169 KB)Jheald (talk | contribs)

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