title: Python Pillow decreasing image brightness changes background
body: <p>I am trying to change image brightness with Python's Pillow (Pillow.ImageEnhance). My images are products on white background (JPEG, RGB) and I want it to remain white regardless of brightness changes.</p>
  <p>When decreasing brightness with Pillow background turns off-white, while if I do the same thing in Photoshop, background stays white.</p>
  <p>Is there any way to preserve white background in Pillow?</p>