Skip to main content

A fast library for rendering HTML/CSS to images

Project description

dynimg

A fast library and CLI for rendering HTML/CSS to images. Use from Python, Rust, or the command line. Built on Blitz, a modular Rust rendering engine.

Perfect for generating dynamic images like Open Graph (OG) images, social media cards, email headers, and more.

Features

  • Python + Rust + CLI: Use from Python, as a Rust library, or command-line tool
  • Multiple output formats: PNG, WebP (lossless), and JPEG
  • High-quality rendering: Configurable scale factor for retina displays
  • Fast: Native Rust performance with no browser overhead
  • Secure by default: Network and filesystem access disabled unless explicitly enabled

Installation

Python

pip install dynimg

Rust CLI

cargo install dynimg

Rust Library

[dependencies]
dynimg = "0.1"
tokio = { version = "1", features = ["rt-multi-thread", "macros"] }

Library Usage

use dynimg::{render, RenderOptions};

#[tokio::main]
async fn main() -> Result<(), dynimg::Error> {
    let html = r#"
        <html>
        <body style="background: linear-gradient(135deg, #667eea, #764ba2);
                     display: flex; justify-content: center; align-items: center;
                     height: 630px; margin: 0;">
            <h1 style="color: white; font-family: system-ui; font-size: 64px;">
                Hello World
            </h1>
        </body>
        </html>
    "#;

    // Render with default options (1200×auto viewport, 2x scale)
    let image = render(html, RenderOptions::default()).await?;

    // Save as PNG
    image.save_png("output.png")?;

    // Or get raw bytes
    let png_bytes = image.to_png()?;
    let webp_bytes = image.to_webp();
    let jpeg_bytes = image.to_jpeg(90)?;

    Ok(())
}

Configuration

use dynimg::RenderOptions;

// Using builder pattern
let options = RenderOptions::default()
    .width(1200)
    .height(630)
    .scale(2.0)
    .allow_net()
    .assets_dir("./assets");

// Or struct initialization
let options = RenderOptions {
    width: 1200,
    height: Some(630),
    scale: 2.0,
    allow_net: true,
    assets_dir: Some("./assets".into()),
    base_url: None,
};

Convenience function

use dynimg::{render_to_file, RenderOptions};

// Render directly to a file (format detected from extension)
render_to_file(html, "output.png", RenderOptions::default(), 90).await?;

CLI Usage

Basic Usage

Render an HTML file to PNG:

dynimg input.html -o output.png

Output Formats

# PNG (lossless)
dynimg input.html -o image.png

# WebP (lossless)
dynimg input.html -o image.webp

# JPEG (lossy)
dynimg input.html -o image.jpg --quality 90

Image Dimensions

The --width and --height options set the viewport size (CSS layout dimensions). The actual output image is scaled by the --scale factor (default: 2x for high-DPI/retina displays).

Output image size = viewport × scale

# Default: 1200px viewport → 2400px output (at 2x scale)
dynimg input.html -o output.png

# OG image: 1200×630 viewport → 2400×1260 output
dynimg input.html -o output.png --width 1200 --height 630

# 1x scale for exact pixel dimensions (1200×630 output)
dynimg input.html -o output.png --width 1200 --height 630 --scale 1

# 3x scale for extra-high-DPI (3600×1890 output)
dynimg input.html -o output.png --width 1200 --height 630 --scale 3

Your HTML/CSS should use the viewport dimensions (e.g., width: 1200px) - the scale factor handles the high-resolution rendering.

Reading from stdin

echo '<html><body><h1>Hello</h1></body></html>' | dynimg - -o output.png

Loading External Resources

By default, network and filesystem access are disabled for security. Enable them to load images, fonts, and other resources:

# Load images/fonts from URLs
dynimg input.html -o output.png --allow-net

# Load images/fonts from a local assets directory
dynimg input.html -o output.png --assets ./assets

# Allow both
dynimg input.html -o output.png --allow-net --assets ./assets

When using --assets, all local paths are resolved relative to the asset directory. Attempts to load files outside this directory will error:

<!-- With --assets ./assets -->
<img src="logo.png">         <!-- loads ./assets/logo.png -->
<img src="img/hero.png">     <!-- loads ./assets/img/hero.png -->
<img src="../secret.png">    <!-- ERROR: outside assets directory -->

For self-contained templates, consider using inline base64 data URIs instead:

<img src="data:image/png;base64,iVBORw0KGgo...">

CLI Reference

dynimg [OPTIONS] <INPUT> -o <OUTPUT>

Arguments:
  <INPUT>   HTML file path or '-' for stdin

Options:
  -o, --output <FILE>       Output image path (format detected from extension)
  -w, --width <PIXELS>      Viewport width in CSS pixels [default: 1200]
  -H, --height <PIXELS>     Viewport height in CSS pixels [default: document height]
  -s, --scale <FACTOR>      Scale multiplier for output (2 = 2x resolution) [default: 2]
  -q, --quality <1-100>     JPEG quality [default: 90]
      --allow-net           Allow network access for loading remote resources
      --assets <DIR>        Asset directory for local resources
  -v, --verbose             Enable verbose logging
      --help                Print help
      --version             Print version

Options can also be set via HTML meta tags (see below). CLI flags override meta tags.

Note: Output image dimensions = viewport × scale. A 1200×630 viewport at 2x scale produces a 2400×1260 image.

Python Usage

import dynimg

html = """
<html>
<style>
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
</style>
<body style="background: linear-gradient(135deg, #667eea, #764ba2);
             display: flex; justify-content: center; align-items: center;
             height: 630px; margin: 0;">
    <h1 style="color: white; font-family: system-ui; font-size: 64px;">
        Hello World
    </h1>
</body>
</html>
"""

# Render with default options
image = dynimg.render(html)

# Save to file
image.save("output.png")

# Or get bytes
png_bytes = image.to_png()
webp_bytes = image.to_webp()
jpeg_bytes = image.to_jpeg(quality=90)

Configuration

import dynimg

options = dynimg.RenderOptions(
    width=1200,          # Viewport width (default: 1200)
    height=630,          # Viewport height (default: auto)
    scale=2.0,           # Output scale factor (default: 2.0)
    allow_net=True,      # Allow network requests (default: False)
    assets_dir="./assets",  # Local assets directory (default: None)
    base_url="https://example.com",  # Base URL for relative URLs (default: None)
)

image = dynimg.render(html, options)

Direct File Output

# Render directly to a file (format detected from extension)
dynimg.render_to_file(html, "output.png")

# With options
dynimg.render_to_file(html, "output.png", options=options)

# JPEG with quality setting
dynimg.render_to_file(html, "output.jpg", quality=90)

Image Properties

image = dynimg.render(html)
print(f"Size: {image.width}x{image.height}")
print(f"Bytes: {len(image.data)}")

HTML Meta Tags

You can configure rendering options directly in your HTML using meta tags. CLI flags take precedence over meta tags.

<meta name="dynimg:width" content="1200">   <!-- viewport width -->
<meta name="dynimg:height" content="630">   <!-- viewport height -->
<meta name="dynimg:scale" content="2">      <!-- output multiplier -->
<meta name="dynimg:quality" content="90">   <!-- JPEG quality -->

This is useful for templates that should always render at specific dimensions. Remember: the output image size is viewport × scale.

Example HTML Template

<!DOCTYPE html>
<html>
<head>
  <meta name="dynimg:width" content="1200">
  <meta name="dynimg:height" content="630">
  <style>
    * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
    }
    .container {
      width: 1200px;
      height: 630px;
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
      font-family: system-ui, sans-serif;
    }
    h1 {
      color: white;
      font-size: 64px;
      margin: 0;
    }
    p {
      color: rgba(255,255,255,0.8);
      font-size: 32px;
    }
  </style>
</head>
<body>
  <div class="container">
    <h1>Hello World</h1>
    <p>Welcome to my site</p>
  </div>
</body>
</html>

Supported CSS Features

dynimg uses Blitz for rendering, which supports:

  • Flexbox and Grid layouts
  • CSS variables
  • Media queries
  • Complex selectors
  • Gradients and shadows
  • Web fonts (via @font-face, requires --allow-net or --assets)
  • Images (requires --allow-net or --assets, or use data URIs)

Performance

dynimg is designed for speed:

  • No browser startup overhead
  • Native Rust rendering pipeline
  • Efficient image encoding

Typical rendering time: 50-200ms depending on complexity.

Development

Building

# Build CLI
cargo build --release

# Build Python wheel
pip install maturin
maturin build --release --features python

# Install locally for development
maturin develop --features python

Running Tests

cargo test
cargo clippy -- -D warnings
cargo fmt -- --check

Releasing

Releases are automated via GitHub Actions. To create a new release:

  1. Update the version in Cargo.toml
  2. Create and push a git tag:
git tag v0.1.0
git push origin v0.1.0

This triggers the release workflow which:

  • Builds wheels for Linux (x86_64, aarch64) and macOS (x86_64, aarch64)
  • Creates a GitHub Release with all artifacts
  • (Optional) Publishes to PyPI (when enabled)

License

MIT

AI Warning

This is AI slop, if you want to use it, fork and make it your own!

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

dynimg-0.1.13.tar.gz (231.5 kB view details)

Uploaded Source

Built Distributions

If you're not sure about the file name format, learn more about wheel file names.

dynimg-0.1.13-cp311-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (9.2 MB view details)

Uploaded CPython 3.11+manylinux: glibc 2.17+ x86-64

dynimg-0.1.13-cp311-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.whl (8.7 MB view details)

Uploaded CPython 3.11+manylinux: glibc 2.17+ ARM64

dynimg-0.1.13-cp311-abi3-macosx_11_0_arm64.whl (7.7 MB view details)

Uploaded CPython 3.11+macOS 11.0+ ARM64

dynimg-0.1.13-cp311-abi3-macosx_10_12_x86_64.whl (8.1 MB view details)

Uploaded CPython 3.11+macOS 10.12+ x86-64

File details

Details for the file dynimg-0.1.13.tar.gz.

File metadata

  • Download URL: dynimg-0.1.13.tar.gz
  • Upload date:
  • Size: 231.5 kB
  • Tags: Source
  • Uploaded using Trusted Publishing? Yes
  • Uploaded via: twine/6.1.0 CPython/3.13.7

File hashes

Hashes for dynimg-0.1.13.tar.gz
Algorithm Hash digest
SHA256 6d9a702db204428783b7a5fa0f9fe3ed07a3256bacb475df70db80542575c926
MD5 e257736c340763fa6825367ecfee0f44
BLAKE2b-256 b101dc6c6893850c06958dd2c80765bd51ac949eca7f7a2dc6368b5f2e65ceea

See more details on using hashes here.

Provenance

The following attestation bundles were made for dynimg-0.1.13.tar.gz:

Publisher: release.yml on blopker/dynimg

Attestations: Values shown here reflect the state when the release was signed and may no longer be current.

File details

Details for the file dynimg-0.1.13-cp311-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.

File metadata

File hashes

Hashes for dynimg-0.1.13-cp311-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
Algorithm Hash digest
SHA256 9242703b3974041d97401178beff0dd9a38c080d4cbce0792e4e33ed4ae13260
MD5 31f1105166fb11b8ede7ce2a077335bd
BLAKE2b-256 890e677fbaacc9542bad09448fb5d6bc71396ac8b7c8dc87034949500a8cccec

See more details on using hashes here.

Provenance

The following attestation bundles were made for dynimg-0.1.13-cp311-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl:

Publisher: release.yml on blopker/dynimg

Attestations: Values shown here reflect the state when the release was signed and may no longer be current.

File details

Details for the file dynimg-0.1.13-cp311-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.whl.

File metadata

File hashes

Hashes for dynimg-0.1.13-cp311-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.whl
Algorithm Hash digest
SHA256 e99aca2a16a7560772ac9f56b192463691252d073287a168cd7d871e943ce388
MD5 679de33b3d99a32bc9a3318f77a1ab9e
BLAKE2b-256 0235140ed360dc002b7c4a49ddf044c32fe704065022572b40c126a5323892fa

See more details on using hashes here.

Provenance

The following attestation bundles were made for dynimg-0.1.13-cp311-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.whl:

Publisher: release.yml on blopker/dynimg

Attestations: Values shown here reflect the state when the release was signed and may no longer be current.

File details

Details for the file dynimg-0.1.13-cp311-abi3-macosx_11_0_arm64.whl.

File metadata

File hashes

Hashes for dynimg-0.1.13-cp311-abi3-macosx_11_0_arm64.whl
Algorithm Hash digest
SHA256 35826f4cba5af1894e88c3123048d4eb6562cd801153098043c1121854dd9dbd
MD5 80cf444df9684a8d8574dd6aa86b1b66
BLAKE2b-256 1b955b2b75d87f2a98c069888c487af8cfce6377b1cd0bb9e74faedb53f43468

See more details on using hashes here.

Provenance

The following attestation bundles were made for dynimg-0.1.13-cp311-abi3-macosx_11_0_arm64.whl:

Publisher: release.yml on blopker/dynimg

Attestations: Values shown here reflect the state when the release was signed and may no longer be current.

File details

Details for the file dynimg-0.1.13-cp311-abi3-macosx_10_12_x86_64.whl.

File metadata

File hashes

Hashes for dynimg-0.1.13-cp311-abi3-macosx_10_12_x86_64.whl
Algorithm Hash digest
SHA256 8e2ae93cccc90c15ea5c6c5fb7f8bc547ff7bdae372b035c72e5137da0b1d015
MD5 e203a7f34897474637df6a3504f54a64
BLAKE2b-256 514960498f69c393c36335c32488bd2e4edd605e3c362cb3cc9bdfb73362dd4f

See more details on using hashes here.

Provenance

The following attestation bundles were made for dynimg-0.1.13-cp311-abi3-macosx_10_12_x86_64.whl:

Publisher: release.yml on blopker/dynimg

Attestations: Values shown here reflect the state when the release was signed and may no longer be current.

Supported by

AWS Cloud computing and Security Sponsor Datadog Monitoring Depot Continuous Integration Fastly CDN Google Download Analytics Pingdom Monitoring Sentry Error logging StatusPage Status page