Are there established work flows / set-ups for when you set up an image on a plane as the background image for your render?
I have a situation where I have set up the background image on a plane but I have a different HDRI in place. It seems that ideally I'd have the same HDRI of the scene taken from the same location as the background image so that all the colours and reflections would be consistent, but obviously this isn't possible 99.9% of the time.
So my question is what do people do in situations like this? How do they approach it? Do you just pick an HDRI that sort of matches the background image? Is every situation different and it's just trial and error to add/do whatever you think is needed to make in the objects in the scene look like they are part of the environment the background image says they are in, or are there established strategies and methods for solving this? Maybe different approaches depending on the type of background image?
p.s. If the CGC staff run sessions to generate ideas for courses then I would love a mini course on common background set-ups and how to achieve them in combination with the compositor
Any time I've worked with an image background I approach it in a similar way as I did when I was doing image manipulation in Photoshop. Mainly, keeping the light/shadow angles, the light color, and the "quality" of the light as closely matched as possible across my source images. If there are no glaring problems with the colors and the shadow directions there is actually a good amount of wiggle room.
It's even easier in Blender since one is able to rotate an HDRI all over the place in order to get the best angle. It's also possible to drop adjustment nodes (HSV, RGB Curve, Brightness/Constrast, etc) after the HDRI in the world shader to really dial things in.
So yep, it's pretty much about picking something close and tinkering until it looks believable. And/or color grade the heck out of it later. :D
When using a billboard(Image on a plane) as the background this is commonly called a flat. As for lighting, usually you don't use an HDRI with a flat. You just setup light objects and turn off receive shadows on the plane. Depending on the image and look you're going for, you can use the image as an emission texture on the plane. Some artist will use an HDRI that matches closely to the feel you want from the lighting. If you're working with an environment team they will sometimes go all out and create an HDRI/Skybox/Sky-dome. Basically you place the camera at the world origin and rotate it 90 on the X axis. Then build your background around the camera. Then you set the camera to Panoramic(This only works in Cycles) then set it to Equirectangular(Equirectangular Cube face if you're going skybox route). The default setting work for 360 degree background. Change Longitude to -90 to 90 for a 180 degree background. Then change output to Radiance HDR file type. Note: the dimensions need to be a a 2 to 1 or width needs to be twice the size of height. also it works best if it's a power of 2 like 1024 instead of 1000 for example. I personally don't create full HDR render, and prefer just the plane or a grid with simple flat shapes.
Thanks all.
I had no idea you could create a flat image from an HDRI so went googling for that and came across the HDRI dome method Dwayne has just mentioned. There's an amazing tutorial below. This comes at the problem slightly differently but essentially solves the problem and then some. In my use case the HDRI dome method is massive overkill but I'm curious and for me at the moment all this is completely new and a learning opportunity so I will go for it.
https://youtu.be/dj6QJtibF4o?si=PtUNjIAgw2GKs6NU
Given the way Blender 5 is going with presents for compositing etc. are things like this something that could be set-up and shared in future so you'd not have to create it and could simply update the HDRIs?
https://superhivemarket.com/products/dome-light-studio?search_id=44257307
and this one seems even better as from what I can tell it does the same thing but does a lot more
https://superhivemarket.com/products/hdri-maker?search_id=44257697
It's already in 5.0. Group it into a node group. Give it a name and right click on the name and click mark as asset. Save it in a folder that is setup as an asset folder. Then In asset browser click the unassigned category on the left. Drag your node group into one of the 3 categories: Camera & Lens Effects, Creative, or Utilities. You will probably want to create an icon for it and add that just like any asset thru the n-panel in the asset browser. Ctrl+s to save the file and it will appear on the asset shelf in the compositor. It's all about putting it in the right category. Note: You can actually put it any category and it will still get added to the asset shelf, but it will only be seen when you select the all at the top. you can add your category thru the 3 lines icon on the asset shelf.