Image and iframe dark mode colour inverter

When toggling dark mode in a TeachBook, images and figures are not inverted by default, but a white background is inserted. However, this white background might not always be desired in dark mode.

The Sphinx-Image-Inverter extension provides a solution by applying an automatic filter to images and iframes. If this filter is not desired for certain items, the Sphinx-Image-Inverter extension provides a solution by allowing selective disabling using the dark-light class.

If the filter should only be applied to a small number of images, this can be done by applying the filter only to items with the dark-light class, in combination with setting inverter_all to true in _config.yml.

[!NOTE] The inversion does not apply to the logo. If a different logo is preferred in dark mode compared to light mode, please use Different logos for light and dark mode.

How does it work?

This Sphinx extension applies a filter such that dark and light colors are switched, however keeps the colours recognizable. This is particularly useful for graphs in which a certain colour is mentioned in accompanying text. Items are not converted if they are marked with the dark-light class (recommended for example for photos).

In more detail, first the colors of the element are inverted, then the hue of the colors is shifted by 180 degrees, so the inverted colors change to their complementary hues. This flips the brightness and contrast, while keeping the hue somewhat recognizable (so a blue line will be a blue line in both ligth and dark mode). Black and white stay inverted (so white becomes black, and black becomes white), because they don’t have a hue. Next, the colors are (by default) saturated to enforce a better contrast. After this, the element blends with the background, making similar colors appear dark and very different colors appear bright. The overall effect creates high contrast between the element and the background, depending on their colors.

Installation

To install the Sphinx-Image-Inverter, follow these steps:

Step 1: Install the Package

Install the sphinx-image-inverter package using pip:

pip install sphinx-image-inverter

Step 2: Add to requirements.txt

Make sure that the package is included in your project's requirements.txt to track the dependency:

sphinx-image-inverter

Step 3: Enable in _config.yml

In your _config.yml file, add the extension to the list of Sphinx extra extensions:

sphinx: 
    extra_extensions:
        - sphinx_image_inverter

Usage

Enable/Disable Inversion of all Images/Figures

By default all images and figures will be inverted. If this is wished for, use the following in your _config.yml:

sphinx: 
    config:
        inverter_all: false

This stops automatic inversion of images and figures. Inversion of specific images and figures can be achieved by enabling this using the dark-light class, see below.

Disable/change saturation

The saturation level is preset to 1.5. If no saturation or a different saturation is requested, use the following in your _config.yml:

sphinx: 
    config:
        inverter_saturation: <saturation>

where <saturation> should be replace with a positive number. The value 1.0 represent no saturation and the value 1.5 is the default value.

Disable/Enable Image/Figure Inversion

By default, when dark-mode is toggled in TeachBook, all images and figures are inverted. To prevent certain images from being inverted, apply the dark-light class. The steps for both Markdown and HTML formats are given below.

For Markdown Format

1. Locate the markdown file that contains the image or figure you want to exclude from inversion.

2. Add the :class: dark-light attribute to the figure directive.

   Example:

   ```{figure} example_folder/example_image.jpg
   :class: dark-light
   :width: 400```
   

For HTML Format

If your image or figure is defined using HTML, apply the dark-light class directly to the tag.

<iframe 
    src="some_figure.html" 
    width="600" 
    height="300" 
    class="dark-light">
</iframe>

Now your image will not be inverted when dark mode is toggled (in the default scenario).

If inverter_all has been set to false, only the image with the dark-light class will be inverted.

Display Text According to Theme

You may want to display different text depending on whether the dark mode or light mode is enabled. To do that, you can use the following classes:

• Light Mode only:

<span class="only-light">Text only visible in Light Mode.</span>

• Dark Mode only:

<span class="only-dark">Text only visible in Dark Mode.</span>

These classes make sure that your text is only visible in the specified modes.

Compatible LaTeX colours

If you'd like to use LaTeX colours which invert similarly, use the approach Sphinx extension Sphinx-Named-Colors.

Contribute

This tool's repository is stored on GitHub. The README.md of the branch Manual is also part of the TeachBooks manual as a submodule. If you'd like to contribute, you can create a fork and open a pull request on the GitHub repository. To update the README.md shown in the TeachBooks manual, create a fork and open a merge request for the GitHub repository of the manual. If you intent to clone the manual including its submodules, clone using: git clone --recurse-submodules git@github.com:TeachBooks/manual.git.