pnggif

Pure-Crystal PNG / APNG / GIF reader.

It decodes an image file (or in-memory buffer) into RGBA bitmaps and, optionally, a downscaled terminal-cell map suitable for solid-block rendering in a TUI (one cell per sampled pixel, the cell background set to the pixel color).

Ported from Blessed's bundled tng.js (MIT).

Features

• PNG: all color types (grayscale, RGB, palette, gray+alpha, RGBA), bit depths 1–16, all scanline filters, Adam7 interlacing, palette transparency. Decompression uses Crystal's stdlib Compress::Zlib.
• APNG: animation frames with dispose/blend compositing.
• GIF (87a/89a): ported LZW decoder, interlacing, transparency, NETSCAPE loop counts, multi-frame animation.
• JPEG / other: converted to PNG via ImageMagick convert when available.
• Cellmaps: nearest-neighbour downscaling with non-square-cell aspect correction (cell_aspect, default 2.0) so images don't look stretched.

Usage

require "pnggif"

img = PNGGIF::PNG.new("picture.png", cell_width: 40)

img.width        # => image pixel width
img.height       # => image pixel height
img.bmp          # => Array(Array(PNGGIF::Pixel)), full-resolution RGBA
img.cellmap      # => downscaled bitmap, one PNGGIF::Pixel per terminal cell
img.frames       # => Array(PNGGIF::Frame)? for animations, else nil

# Pre-composited animation frames ({cellmap, delay_ms}):
if frames = img.animation_cellmaps(40)
  frames.each { |cellmap, delay_ms| ... }
end

Each PNGGIF::Pixel has r, g, b, a channels (0–255).

License

AGPLv3