monolens

View part of your screen in monochrome colors or in simulated protanopia, deuteranopia, or tritanopia.

Watch the demo on YouTube.

Install with pip install monolens and then run monolens in a terminal or do it in one command with or pipx run monolens.

Usage

• Drag the lens around by holding a Mouse button down inside the window
• To quit, press Escape, Q, or double click on the lens
• Resize the lens by pressing up, down, left, right
• Press Tab to switch between monochrome view and simulated protanopia, deuteranopia, tritanopia
• Press I to switch view label on/off
• To move the lens to another screen, press M

On OSX, you need to give Monolens permission to make screenshots, which is safe.

Known limitations

• The app is tested on OSX and Linux. It may flicker when you move the lens (less so on OSX). If you know how to fix this, please help. :)
• Pulling the lens to another screen is currently not supported. Press S to switch screens instead.
• The lens actually uses a static screenshot which is updated as you move the lens around. This trick is necessary, because an app cannot read the pixels under its own window. Because of this, the pixels under the app are only updated when you move the lens away first and then back.
• On OSX, an ordinary app is not allowed to read pixels outside of its window for security reasons, which is why this app needs special permissions. Doing this is safe; Monolens contains no networking code and will neither store nor send your pixels anywhere.

Future plans

• Support gestures to rescale the lens (pinch etc)