You should allow the user to specify a pixel ratio that describes the width/height of each character of their terminal font. Otherwise, your images will be distorted, because your output pixels are not square.

Here's a screenshot demonstrating this issue, when converting a GIF to text in a terminal:

https://monosnap.com/file/HwrGbSHEwxWlTQCCeXyd9qcFxwL38V.png

On the left, the original image. In the center, a ratio-perserved resized render in a terminal On the left, a pixel-ratio aware resized render.