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| View Original: | Kcc_rescale_01_im_point.jpg (557x425) | |||
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| Keywords: Kcc rescale 01 im point.jpg 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 <p> The image on this page was resized to 50 using Image Magick 6 7 5 with the point option -- i e merely retaining every other pixel decimation The result is very similar to the GIMP no interpolation option interaction between spatially repeated structures in the engraving and the finite resolution has resulted in a highly visible Moiré pattern Moiré banding pattern becoming apparent in the sky the clouds and the building on the right the result of spatial aliasing Compared to the GIMP result the phase of the Moiré fringes appears to be shifted by 180 degrees -- presumably because IM chooses to retain a different point of the four possible candidates <p> Other images in the series look at the results of using various available lowpass filter s to try to minimse or suppress such artefacts 1801 F Roffe after P Nash 1801 - King's College Chapel - sanders13001 jpg an engraving first published in 1801 John Roffe 1769-1850 engraver after Frederick Nash 1782 “1856 File Kcc rescale 01 gimp no interpolation jpg -- GIMP by decimation File Kcc 01 im point jpg -- ImageMagick by decimation File Kcc rescale 02 im box filter jpg -- ImageMagick using a box filter File Kcc rescale 03a Gimp bicubic interpolation jpg -- GIMP using a bicubic filter allegedly File Kcc rescale 03b Gimp lanczos interpolation jpg -- GIMP using a Lanczos filter allegedly File Kcc rescale 04 im triangle jpg -- ImageMagick using a ramp filter File Kcc rescale 05 im Lanczos jpg -- ImageMagick using a Lanczos filter File Kcc rescale 06 im default jpg -- ImageMagick default a Mitchell filter Source code convert kcc jpg -filter point -resize 50 kcc_im_point jpg PD-old-100 Uploaded with UploadWizard Aliasing | ||||
