Using a transparent image you can brighten, dim, or color the objects behind it. If you also use a subtle pattern in the image you can obtain other effects (i.e. fog, smoke, etc.)
Scene with semi-transparent image with pattern (spray painted):
You can also take a snapshot of your scene (F10), hiding those items you don't want blurred, and use an image editor to blur it, then place it back on the stage and size and position.
Background all blurred:
Partial background blurred (note flowers on bench behind Cherry):
See my CTA Tutorials on the YouTube channel CTAStepByStep
Check out EZColors for CTA. The easy way to change Render Styled (RS) colors.
5 Years Ago by