ham_convert 1.2.2

New in this update: improved and optimized triple mode and added line checks dithering designed to look better in HAM6 than standard dithering methods.

ham_convert 1.2.2

Download:
Main mirror (all stable and testing versions)
External mirror

Changelog:

Triple mode: faster calculation. Improved set color selection for the first pixel column.
Triple mode: added checking the +1 and -1 modify values in addition to the quantized value from the source image. It was recycled from the failed multi-pixel CIEDE HAM6 experiments from the 2015. It reduces some multi-channel color transitions that are too rapid to be reproduced. Dual mode and its extension (triple mode) are also recycled from these experiments.
Checks dithering (normal “dots” version and “lines” variant more suitable for HAM6).
Checks dithering is a type of ordered dithering that almost doubles the number of shades per channel by creating one intermediate shade between every two by alternating pixels with these two shades to form a checkerboard. It differs from other ordered dithering methods by its use of only solid colors or a 1:1 mix of two colors in the form of a checkerboard pattern. This makes the dithering less visible and more natural-looking.
Checks “lines” variant is designed to better look in the HAM6 mode plagued by horizontal pixel color restrictions (16 palette colors or modification of only one color channel at the same time). Instead of using a checkerboard pattern it operates by alternating shades on successive lines (pixels from different lines are independent in HAM6, they’re dependent only in same line). Increases the number of shades per channel from 16 to 31 to form a pseudo-15-bit mode using HAM6. It’s also more compressible than the normal checks variant.
A modified “lines-mixed” version with less visible pattern and better reproduction of the details in the darkest areas is available in the 1.2.3 beta.
Remaining time estimation.
Palette generator fixes and code optimization.
Normal checks dithering pattern – difficult to reproduce in HAM6 because it makes pixels from the same line more variable than in the original image

Checks dithering operating on lines can be reproduced in HAM6 because pixels from the same line remain similar

Test images:

Color patterns RGB888 (original)

HAM6 with no dithering

HAM6 with floyd-steinberg dithering - standard dithering methods perform poorly due to HAM color restrictions

HAM6 with floyd-steinberg dithering – standard dithering methods are unreliable due to HAM horizontal color restrictions

HAM6 with checks (lines veriant) dithering - this method was specially designed around HAM color restrictions and thus looks clearer and is more reliable

HAM6 with checks (lines variant) dithering – this method was specially designed around HAM horizontal color restrictions and thus looks clearer and is more reliable