Write a darken_filter and change_picture function that modifies the pixels in the left half of the image to be darker. You can darken a pixel by subtracting the same value from each of the red, green, and blue values of the pixel.

for every pixel in the left half of the image
set pixel red to be (red - DARKENING_FACTOR)
set pixel green to be (green - DARKENING_FACTOR)
set pixel blue to be (blue - DARKENING_FACTOR)

(PYTHON)