Put manga on your Kindle, the right way

A CBZ carries no notion of direction, and a Kindle presented with a plain sequence of images assumes left to right. That is the root of the backwards-manga problem: the pages are in the correct order, but the device advances toward the wrong edge, so the second page of each spread appears before the first.

EPUB 3 fixes this with a single attribute on the spine, and Amazon's conversion carries it through into the Kindle book. Tanko sets it from the direction toggle and nothing else — it cannot be inferred from the images, which is why the control is always visible on the converter rather than hidden behind an auto setting.

Direction also decides how spreads are split. With right to left selected, the right half of a landscape page becomes the first of the two output pages; with left to right it is the left half. Convert a manga volume as left to right and every split spread comes out reversed as well, so the toggle has to be right before you convert, not after.

On a portrait e-ink panel a whole spread gets shrunk until its width fits, which leaves it roughly a third the height of the screen with lettering too small to read. Splitting gives each half the full panel, at the cost of the artwork that crosses the gutter — the same compromise the printed book already makes.

Auto mode counts landscape pages across the whole volume by reading image headers before decoding anything. When they are a minority they are treated as spreads and split; when more than half the pages are landscape, the book is treated as landscape-format and nothing is split. The result panel reports how many spreads were split so you can sanity-check it.

Always split and Never split exist for the exceptions: an artbook with a handful of two-page paintings you want intact, or a scanlation where the scanner joined every page into pairs. Both apply to the whole file, so convert volume by volume when volumes differ.

Manga is drawn for black ink on white paper, and e-ink panels reproduce 16 shades of gray. Tanko converts each page with Rec. 601 luma, darkens midtones with a gamma of 1.8 because e-ink washes them out, and then quantizes to those 16 levels with Floyd-Steinberg dithering so gradients on screentones do not band.

Scanned volumes also pass through a levels correction that maps the paper tone to white and faded ink to black using the 1st and 99th percentiles of each page, skipping pages that are already clean or nearly uniform, such as a black flyleaf. On a Colorsoft the grayscale steps are skipped and the page is kept in color.