I posted this to lighting and rendering, but no replies…so, …
I use Blender to make simple animations, often with 3D objects moving around in front of a flat 2D background image.
Back in 2.79, I could set the shadows for the background image object so that it would not “Receive” shadows, because that makes it obvious that the background is flat.
Now, in 2.82 Eevee, that ability has disappeared.
So, does anyone know how to turn off “Receive” shadows for an object?
Thank you.
I’m not sure if that option exists, but one way to do it would be to give the backdrop an emission shader with a value of 1 (you can also use other values to make it lighter or darker). The emission shader does not receive shadows or reflections etc. Use your background image in the colour input.
Thanks DNorman! Exactly what I needed.
I need to learn more about shading and nodes.
DNorman, I have a follow up question if you don’t mind
Back in 2.79 - if I had a character walking in front of a backdrop, I could add a “ground” plane that was set to be “Shadow Only” . (To give the appearance that there IS a shadow on the backdrop.)
Is there a “Shadow Only” shader? I tried a Transparent BSDF shader, but the ground plane is completely black. I tried hooking up a Principled BSDF just for for fun, but that makes the plane purple - but I do see the shadow that I want.
Thank you.
Express way, duplicate the object and set the one of it to the shadow cather… It will leave the shadow only
Ha, ha, that’s a bit like having your cake and eating it!
I take it you want a shadow plane in a defined part of the image, being transparent and only “receiving” shadows.
Again I am not sure if there is an easier way of doing this for Eeveey, but you could make a shadow catcher, explained here:
As explained in the video depending on the light source you may find that you see unwanted parts of the shadow catcher. If you do not want to change the light intensity you can change the position of the white colour slider to contrast the effect. The black/grey slider value changes the opacity of the shadow.
I had to look this up so credit for this answer is for Jeannot Landry the author of the video.
in this image I made a circular “shadow catcher” and placed it on top of an emission plane.
You can see the shadow is only showing on the circle. I can not find any reference to the “express” way mentioned by Giri for Eveey.
DNorman,
Thank You so very much for the effort!
This looks pretty good after a quick trial, I will play around with it
Your welcome, I learnt something too! 
One more question, if you please…
This only works with a Sun Lamp for me. (in Eevee)
Same for you?
Thanks again !!, Cal
OOPS - I was wrong. Only works with Sun in viewport, all other lamps are not so obvious, but renders the way I would have expected.
Blender is sooooo kookie, ya know?
It is not that it does not work in viewport, «material preview» mode by default uses an hdri to light the scene, the hdri does not give any shadows. You can choose to use the hdri in this mode or turn it off in the drop down menu at the end of the viewport icons. To get shadows in Eeveey you have to use lamps. If you want the viewport to resemble the render results you have to check the two boxes in the drop down menu as shown.
Here the default hdri (no shadows):
OK.
Thanks again for all your help.
