Rounding error in Posterize

[seahen]

This bug can be reproduced by opening the chart from https://upload.wikimedia.org/wikipedia/commons/b/b8/RGB_24bits_palette_color_test_chart.png, clicking Adjustments > Posterize, and setting the number of levels to 32. Since 255 * 29/31 = 238.538, this should round up to 239 for the third-brightest primary green. Instead, it comes to 238, indicating that Pinta is rounding down rather than to the nearest level.

(I encountered this while applying Posterize to some images with unequal level counts, to test whether unequal color depths such as RGB 453 might be better for displays where less than 15-bit color is available. Since 255 * 14/15 = 238 exactly, the results imply that RGB 453 can reproduce some shades of secondary yellow exactly which it cannot.)