ImageUtil

ImageUtil is a lightweight Ruby library focused on manipulating images directly in memory. Its primary goal is to help scripts visualize data right in the terminal by supporting SIXEL output alongside common image formats. The API is still evolving and should be considered unstable until version 1.0.

require 'image_util'

# 40×40 RGBA image
img = ImageUtil::Image.new(40, 40)

An optional block receives pixel coordinates and should return something that can be converted to a color. Dimensions of more than two axes are supported.

img = ImageUtil::Image.new(128, 128) { |x, y| ImageUtil::Color[x, y, 40] }

Instead of building an image from scratch you can load one with ImageUtil::Image.from_string or ImageUtil::Image.from_file. Both helpers understand the built in codecs for png, jpeg, pam, gif and apng formats:

img = ImageUtil::Image.from_file("logo.png")
data = ImageUtil::Image.from_string(File.binread("logo.jpeg"))

A from_file method also supports passing IO objects:

img = ImageUtil::Image.from_file(IO.popen("magick rose: png:"))
img.draw_line([0,0], [69,45], :blue)

The same formats can be written back using to_string or to_file. When saving to a file path, to_file can infer the format from the file extension.

img.to_file("out.png")
binary = img.to_string(:jpeg)

After loading or creating an image, you can access information about it, like dimensions or color bits.

img.dimensions # => [20,30]
img.width # => 20
img.height # => 30
img.color_bits # => 8 (means every channel has 8 bits of color)
img.channels # => 3 (RGB)

Images can be previewed in compatible terminals:

puts ImageUtil::Terminal.output_image($stdin, $stdout, img)

In irb or pry the inspect method shows the image automatically, so you can just evaluate the object:

img

The library checks if the Kitty graphics protocol is available and falls back to SIXEL otherwise. Kitty graphics protocol is supported by Kitty, Konsole and a couple others. SIXEL, most notably, works in Windows Terminal, Konsole (KDE), iTerm2 (macOS), XTerm (launch with: xterm -ti vt340). Here's how SIXEL looks in Konsole:

This library supports generating Sixel with either libsixel, ImageMagick or using a pure-Ruby Sixel generator. For best performance, try to install one of the earlier system packages. Both Kitty and SIXEL outputs also accept one-dimensional images, treating them as height 1.

ImageUtil::Color.from (also known as ImageUtil::Color.[]) accepts several inputs:

• Another Color instance
• Arrays of numeric components ([r, g, b] or [r, g, b, a])
• Numbers (used for all RGB channels)
• Symbols or strings containing CSS color names (:rebeccapurple, 'papayawhip')
• Hex strings like '#abc', '#aabbcc' or '#rrggbbaa'

When numeric components are given, integers are first clamped to the 0..255 range. Float values are treated as fractions of 255, so 0.5 becomes 127.5 and 1.0 becomes 255. After scaling, values are again clamped to this range. If the alpha channel is omitted it defaults to 255.

ImageUtil::Color[0.5] # => #808080
ImageUtil::Color[:red] # => #ff0000
ImageUtil::Color["#fc0"] # => #ffcc00

Note that whenever the library expects a color, it may be given in any form accepted by this function.

Pixels can be accessed with integer coordinates or ranges. When ranges are used a new Image containing that region is returned and can be modified separately.

img[0, 0] = '#ff0000'
patch = img[0..1, 0..1]

For instance, you can extract a region, edit it and paste it back:

img = ImageUtil::Image.new(128, 128) { [0, 0, 0] }
corner = img[0..32, 0..32]
corner.all = :green
img[0..32, 0..32] = corner
img[2, 2] = :yellow
# img.to_file("pixel_patch.png", :png)
img

Assigning an image to a range automatically resizes it to fit before pasting.

On the other hand, if you assign a color to a range, it will fill all referenced pixels with that color (draw a rectangle).

Iteration helpers operate on arbitrary ranges and share the same syntax used when indexing images. each_pixel yields color objects, while each_pixel_location yields coordinate arrays. set_each_pixel_by_location! assigns the value returned by the block to every location (unless nil is returned).

# create an all-black image
img = ImageUtil::Image.new(128, 128) { :black }

# fill a checkerboard pattern
img.set_each_pixel_by_location! do |x, y|
  :red if (x + y).odd?
end

# count how many red pixels were set
black = img.each_pixel.count { |c| c == :red }

# display img in terminal
img

Note that instead of manually calling set_each_pixel_by_location, you can just pass a block to ImageUtil::Image.new.

ImageUtil::Image ships with a few convenience filters. Each bang method modifies the image in place while the non-bang version returns a copy.

Flatten an RGBA image on a solid color.

# create a transparent image gradient containing shades of red only
img = ImageUtil::Image.new(128, 128) { |x, y| [255, 0, 0, x + y] }

# put it on a blue background
img.background!([0, 0, 255])
# img.background([0, 0, 255]) # returns a new image

Place one image over another. When respect_alpha is true, the pasted pixels are blended with the base image.

base    = ImageUtil::Image.new(128, 128) { |x, y| [x, y, 50] }
overlay = ImageUtil::Image.new(64, 64)  { |x, y| [255, 0, 0, (x + y) * 2] }
base.paste!(overlay, 32, 32, respect_alpha: true)

Draw simple shapes directly on the image.

img = ImageUtil::Image.new(128, 128) { [0, 0, 0] }
img.draw_line!([0, 0], [127, 127], :red)
img.draw_line!([0, 127], [127, 0], :lime)
img.draw_circle!([64, 64], 30, :blue)

Scale an image to new dimensions.

img = ImageUtil::Image.new(128, 128) { |x, y| [x, y, 30] }
img[20, 20] = img.resize(64, 64)
img
# img.resize!(64, 64) # modifies in place

Reduce the image to a limited palette.

img = ImageUtil::Image.new(128, 128) { |x, y| [x * 2, y * 2, 200] }
img.palette_reduce(64)

Rotate or flip an image.

img = ImageUtil::Image.new(128, 128) { |x, y| [x, y, 0] }
img.flip!(:x)
img.rotate!(90)
# img.rotate!(90, axes: [:x, :z])

Multiply all pixels by a color.

img = ImageUtil::Image.new(128, 128) { [255, 255, 255, 128] }
img * :red

Overlay text using the bundled bitmap font.

img = ImageUtil::Image.new(128, 128) { [0, 0, 0] }
img.bitmap_text!("Lorem ipsum dolor sit\namet, consectetur adipiscing\nelit.", 2, 2, color: :blue)

Change how many dimensions an image has or adjust their size.

img = ImageUtil::Image.new(64, 64) { :white }
img.redimension!(128, 128) # can also add additional dimensions
img.background(:blue)

The gem includes a small image_util CLI. Run image_util support to list available codecs, default format handlers and detected terminal features. See docs/cli.md for details.

After checking out the repo, run bin/setup to install dependencies. Then run rake spec to execute the tests. You can also run bin/console for an interactive prompt for experimenting with the library.

Run bin/benchmark to execute a small benchmark.

Bug reports and pull requests are welcome on GitHub at https://github.com/rbutils/image_util.

The gem is available as open source under the terms of the MIT License.