Press the green flag and enter a blur size. It's super fast on Turbowarp: https://turbowarp.org/508461477 Note: the first time the project runs it's a bit slower since the project has to load and decode the image from a variable to get around list size limitations.
This is a pen-based implementation of a "box blur". It basically takes the average of the pixel values in a square around each pixel. This can be done in two passes, left-to-right and bottom-to-top. Due to the way the average is calculated, all blur amounts are the same speed to calculate. There are faster stamping-based blur methods on Scratch, but this seemed more interesting to me.
