Image URL: You can use here a fullscreen image (like from Unsplash), a pattern (like Subtle Patterns) or a little non-repeatable image (like your logo).
Scaling: chose the option that fits your background image.
Luminosity: You can choose Darker or Lighter, depending if you have a dark or light image background.
Luminosity level %: ;How much luminosity you want to apply over your background image? Apply the amount needed to increase your form readability, like below:
