# Last edited on 2020-11-07 16:32:26 by jstolfi Test images for affine comparison. They are derived from a color magazine page scanned at 600 dpi. They are all 128x128 pixels, 8 bits per sample, centered at about the same point of the page (±2 pixels), at the end of a black pen stroke. The following images of the same feature are "rgb-128-{NN}.png" (color) and "gray-128-{NN}.png" (grayscale), all 128x128 pixels. The "center" column is the pixel that corresponds to the center of the {NN="01"} image. NN center displac description -- ----------- ----------- --------------------------- 01 64.00 64.00 00.00 00.00 page scan, cropped. 02 63.20 65.20 -0.80 +1.20 re-scan of the same page, shifted on scanner, cropped. 03 62.35 64.76 -1.65 +0.76 image scan-02.png rotated by 60 degrees ccw about center. 04 62.00 62.00 -2.00 -2.00 image scan-01.png magnified to 200% with gimp about center and cropped. 05 64.50 64.20 +0.50 +0.20 same scan of scan-01.png, reduced to 50% with gimp and cropped. The images "rgb-600-{NN}.png" are larger independent scans of the same drawing, at different dots-per-inch resolution. Images "01" to "03" were contrast-enhanced (25 points) with Gimp. Image "04" was not contrast-enhanced but instead was darkened (-25 points). NN center displac description -- ------------- --------------- --------------------------- 01 300.00 300.00 0.00 0.00 scan at 600 dpi, contrasted, cropped. 02 299.93 299.61 -0.07 -0.39 scan at 300 dpi, rotated ~60 deg cw, contrasted, cropped. 03 500.00 200.00 +200.00 -100.00 same scan of 02, contrasted, cropped by displaced window. 04 300.00 300.00 0000.00 0000.00 rescan at 600dpi, darkened, cropped. ( 300.000000 300.000000 ) 20.000 0.000 = ( 299.930074 299.615424 ) 10.000 60.000 ( 288.000000 195.000000 ) 20.000 0.000 = ( 342.926212 269.371286 ) 10.000 60.000 ( 448.000000 321.000000 ) 20.000 0.000 = ( 326.841962 370.060404 ) 10.000 60.000 ( 300.000000 244.000000 ) 20.000 0.000 = ( 332.234680 294.747437 ) 10.000 60.000