DaltonLens

DaltonLens is a desktop application that assists colorblind individuals by providing real-time color filters, pixel color information, and similar-color highlighting tools. It runs as a tray program on macOS, Windows and Linux, offering color deficiency simulation, the daltonize algorithm to enhance color discrimination, and screen region capture with adjustable filters.

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• Daltonize filter. Applies a transformation that shifts color differences into chromatic channels distinguishable by people with deuteranopia, protanopia or tritanopia. The algorithm redistributes lost color information, improving readability of diagrams, heatmaps and dashboards.
• Color information under pointer. When activating the global overlay with Ctrl+Alt+Win+Space, displays the color name (e.g. "brick red"), its hexadecimal value and the perceptual distance to the two closest named colors. Helps identify confusing hues in user interfaces and documents.
• Highlight similar color pixels. After capturing a screen region, the user clicks on a pixel and the tool illuminates all pixels with a similar color within an adjustable threshold. Uses adaptive filters to handle anti-aliased edges and line plots, especially useful for reading legends and curves in scientific reports.
• Online color blindness simulator. Web version that allows uploading custom images or using predefined examples to visualize how a person with deuteranopia, protanopia or tritanopia perceives the image. Implements multiple simulation methods compared for accuracy, based on the DaltonLens-Python library.
• Region capture with applied filters. Allows selecting a rectangular screen area (or the full window with the spacebar) and applying any color filter to that capture. The result appears in a separate window, where the filter can be changed in real time without recapturing.
• HSVTransform filter. Modifies the image using three independent parameters: saturation boost (up to 200%), hue shift (in degrees) and quantization of hue values to reduce the number of distinct colors. Facilitates separation of color categories in statistical charts.
• Shift key for original view. At any moment while viewing a filtered image, holding the Shift key shows the original unfiltered image. Releasing Shift returns to the active filter. Allows immediate comparison of the color correction effect.
• Instant global overlay. The program runs in the system tray and responds to a global shortcut (Ctrl+Alt+Win+Space) without needing to focus the application window. The overlay shows color information under the cursor and allows starting region capture with a click and drag.
• Integrated help window. Displays all available keyboard shortcuts, the operation of each tool and adjustable filter parameters. Opens automatically on first startup and can be accessed at any time from the tray menu.
• Multiple monitor support. Automatically detects the monitor where the mouse pointer is located and captures or shows the overlay on that monitor. Works in extended desktop configurations without manual setup.
• Perceptual distance to named colors. Inside the color information overlay, calculates the distance in CIELAB space (delta E 2000) between the pixel color and a database of 160 commonly named colors. Shows the two closest names and their distance, helping color-blind people describe colors.
• Color deficiency simulation filter. Applies transformations to the entire image that simulate how a person with protanopia (red blindness), deuteranopia (green blindness) or tritanopia (blue blindness) would see it. Allows validating whether a visual design is accessible before publishing.
• Persistence of daltonism type in Daltonize filters. When selecting the Daltonize filter, the application remembers whether it was configured for deuteranopia, protanopia or tritanopia across different capture sessions. No need to reconfigure the type each time a new image is opened.
• Corrected color space support (Judd-Vos). The RGB to LMS (cone response) conversion uses the transformation matrix with Judd-Vos correction for the standard observer, improving perceptual accuracy of simulations and daltonization filters compared to older methods.

The DaltonLens project was created by Nicolas Burrus, a software engineer with interest in color perception and accessibility. Development began in 2019 as a response to the lack of free desktop tools to assist colorblind people beyond simple hue-shift filters. The first public version was released in 2020 with support for Windows and macOS, adding Linux support in 2021. The application is written primarily in C++ for the image processing core and screen capture, using the GLFW library for windows and events, and libappindicator for the tray icon on Linux. Additionally, the project includes libDaltonLens, a standalone C library (public domain) that implements color blindness simulation and daltonization algorithms. The command-line version and research notebooks are written in Python (DaltonLens-Python).

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