Overview
pngcanvas is a minimalist Python library for generating PNG images from scratch without Pillow, ImageMagick, or any other dependency. Draw lines, filled rectangles, text, and basic shapes using a simple canvas API, then write the result to a PNG file. Originally built for constrained environments — embedded systems, serverless functions, CGI scripts — where pulling in a full imaging library is impractical. ★44 with 9 forks, still referenced regularly.
How it works
The library implements the PNG format spec directly: an IHDR chunk, IDAT chunk (with raw pixel data compressed via the Python standard library's zlib), and IEND chunk. Drawing operations modify an in-memory RGBA pixel array. Text rendering uses a bundled bitmap font. The resulting PNG is written to any file-like object — no temp files, no external processes.
Features
Zero dependencies
Uses only the Python standard library — zlib for compression, struct for binary packing. Works on any Python 2.7+ or 3.x.
Drawing primitives
Lines, filled and outlined rectangles, circles, and arbitrary polygon fills via scanline rasterisation.
Bitmap text
Bundled bitmap font for rendering ASCII labels directly onto the canvas — useful for charts and diagrams.
Any file target
canvas.dump(fileobj) writes to any file-like object — disk file, BytesIO buffer, HTTP response body.
Single-file library
The entire library is one Python file — copy it into your project and import it with no installation.
Architecture
Posts
2026-04-25
Python