Show HN: Using 2D DFT, dithering, etc. to maximize eInk manga image quality

Kindle Comic Converter (KCC) is a cross-platform tool that optimizes comics and manga for e-ink devices like Kindle, Kobo, and ReMarkable, producing fixed-layout files that display full-screen without margins. It accepts images, archives (CBZ/EPUB), and high‑resolution PDFs and outputs MOBI/AZW3, EPUB/KEPUB, CBZ, PDF, or image folders. The main goal is to maximize perceived image quality while drastically reducing file size and improving performance on memory‑constrained readers: for example, downscaling large Humble Bundle PDFs to a device’s native resolution can compress a 600 MB volume to around 100 MB, speed page turns, and extend battery life. KCC also offers semi‑automatic spread detection, rotation and split options, many user-friendly settings with tooltips, and both GUI and command‑line variants for power users.

KCC applies perceptual and device‑specific processing to fix common ereader problems: it corrects gray or faded blacks, handles 2‑page spread composition, and uses dithering and 4‑bit image formats (PNG/WEBP) to reach visually lossless results at roughly half the size of 8‑bit JPEGs. A 2D Discrete Fourier Transform method addresses color artifacts on Kaleido 3 color e‑ink without blur. Optional KOReader workflows and jailbreaking unlock better formats and faster conversions. Notes and caveats include Kindle Scribe format quirks, recommended transfer methods, prerequisite tools for some features, and active maintenance with release builds for major platforms.