I want to create an image like the one below, based on a specific matrix where 4 is green, 3 is blue, 2 is yellow and 1 is red.

The image would be 18 columns and 22 rows and the data would be uploaded using a txt file. The data would be between 4-1 and be automatically color coded once the file is ran

image example matrix

I was referencing this code from here for help Plot a matrix, values as colors but I am confused on how to go about fixing the loop and integrating a text file instead of an actual random matrix. any assistance or guidance would be appreciated