Image Processing in Ruby with GD: Exploring ruby-libgd v0.3.0

March 4, 2026

Image processing is usually associated with languages like Python or C++, but Ruby can also manipulate images efficiently thanks to bindings for native libraries.

One of those libraries is libgd, a well-known C library used to dynamically generate and manipulate images such as PNG, JPEG, and GIF. It has historically been used in web applications to generate charts, thumbnails, and dynamic graphics.

The Ruby gem ruby-libgd provides a native Ruby interface to this library.

Version 0.3.0 expands the filtering capabilities significantly by adding convolution filters, color filters, and scatter effects.

In this article we’ll explore what’s new and how to use these features.

Installing the Gem

The gem is available on RubyGems, the standard package system used to distribute Ruby libraries.

Install it with:

gem install ruby-libgd

Then require it in your project:

require "gd"

Loading an Image

Let’s start with a simple example.

require "gd"
img = GD::Image.import("cat.jpg")
img.save("output.jpg")

Now we can begin applying filters.

What’s New in ruby-libgd v0.3.0

The new version introduces three major improvements:

1. Convolution Filters

These filters apply a matrix (kernel) across pixels.

New filters include:

• sobel
• sharpen
• laplacian
• box_blur
• gaussian_kernel
• emboss2

2. Color Manipulation

New support for:

• colorize
• RGB deltas
• alpha channel adjustment

3. Scatter Effects

Two new filters introduce random pixel displacement:

• scatter_color
• scatter_ex

Together these make ruby-libgd far more capable for image analysis and artistic effects.

Understanding Convolution Filters

A convolution filter processes each pixel using its neighbors.

Example kernel:

0  -1  0
-1  5 -1
0  -1  0

This is a sharpen filter.

The kernel is applied to every pixel to calculate the new value.

ruby-libgd exposes this through the underlying GD convolution API.

Example: Edge Detection with Sobel

The Sobel filter detects edges by measuring intensity gradients.

require "gd"
img = GD::Image.import("cat.jpg")
img.filter(:sobel)
img.save("sobel.jpg")

This highlights edges in the image.

Example: Gaussian Blur

Gaussian blur smooths an image.

img = GD::Image.import("cat.jpg")
img.filter(:gaussian_kernel)
img.save("gaussian.jpg")

Gaussian kernels produce smoother results than simple box blur.

Example: Box Blur

Box blur averages neighboring pixels.

img = GD::Image.import("cat.jpg")
img.filter(:box_blur)
img.save("box_blur.jpg")

This produces a soft blur effect.

Example: Emboss Filter

Emboss filters create a relief effect.

img = GD::Image.import("cat.jpg")
img.filter(:emboss2)
img.save("emboss.jpg")

Edges appear raised, giving a 3D-like appearance.

Example: Colorize Filter

Colorize modifies the RGB values of the image.

img = GD::Image.import("cat.jpg")
img.filter(:colorize, 255, 0, 0, 50)
img.save("colorize.jpg")

Parameters represent:

red_delta
green_delta
blue_delta
alpha

This example applies a red tint.

Example: Scatter Effects

Scatter filters randomly move pixels.

scatter_color

img = GD::Image.import("cat.jpg")
colors = [
  GD.true_color(255,0,0),
  GD.true_color(0,255,0),
  GD.true_color(0,0,255)
]
img.filter(:scatter_color, 2, 5, colors)
img.save("scatter_color.jpg")

scatter_ex

img = GD::Image.import("cat.jpg")
img.filter(:scatter_ex, 2, 10)
img.save("scatter_ex.jpg")

These filters produce interesting artistic effects.

Included Example Scripts

The gem now includes multiple example programs demonstrating the filters:

box_blur.rb
colorize_rgb_deltas.rb
colorize_alpha_deltas.rb
convolve.rb
emboss2.rb
gaussian_kernel.rb
laplacian.rb
sobel.rb
sharpen.rb
scatter_color.rb
scatter_ex_01.rb
scatter_ex_02.rb

These scripts provide a good starting point for experimenting with image processing.

Why This Update Matters

The new filters transform ruby-libgd from a simple wrapper into a more capable image processing tool.

Developers can now use Ruby for:

• edge detection
• blur effects
• artistic transformations
• convolution experiments
• generative art

All while leveraging the performance of a native C library.

Project Links

GitHub repository:

RubyGems page:

Conclusion

ruby-libgd v0.3.0 significantly expands the capabilities of the GD bindings for Ruby.

With convolution filters, color manipulation, and scatter effects, it becomes a useful tool not only for web image generation but also for experimenting with image processing techniques directly in Ruby.

If you enjoy combining Ruby with graphics or generative art, this update opens many interesting possibilities.