Fusion Merge Node

I'm working on a clip where I need to add some flames to a burning car. I have about 6 flame/smoke elements I have added to the car and since it is in the background I want to add a blur to it so that it matches the camera's depth of field.

When I add a blur before my merge node the flame elements get cropped. Upon further investigation, I see that my merge node is not the same resolution size as the fusion project I am working in. I have a 5K clip and the merge node looks like the edges are set to 1080x1920 (9x16) resolution. When I apply the blur it crops all my elements to this 9x16 size merge node. If I scale up and rotate the merge note it affects the nodes behind it as normal.

What is the recommended way to add a lens blur node that will not crop my nodes? Is there a setting I am missing?

Node Layout

Screenshot 2022-08-09 092830.jpg (69.54 KiB) Viewed 1196 times

Merge Node Crop

Screenshot 2022-08-09 093003.jpg (9.36 KiB) Viewed 1196 times

If I'm working with footage that are different sizes, I usually always start with a background node set to the size I want the final frame to be. Then I merge the elements in front of the bg node and place them accordingly. this way when I do a filter or merge it back on, it all lines up fine.

Additionally, I set the alpha of the bg node to 0, but if you're adding fire, you can just screen it back on or whatever.

added bg

fix_1.PNG (575.87 KiB) Viewed 1124 times

EDIT: Looking at your flow again, I see you have things going into the BG input of a merge and that merge going into the bg of another merge. You can just remove that merge with the empty FG input and plug it right into the BG of the other merge. Ive attached two images to demonstrate

this doesnt require the BG node, but still isnt as straight forward as the other method

fix_2.PNG (572.28 KiB) Viewed 1124 times

Super Helpful, Thanks. - I'll get these Node things soon enough. coming from After Effects and Premiere.

Screen is a naughty word! The correct way to composite emissive elements is to add. Screen is a hack made necessary by working in 8-bit integer color. If you're working in float, screen can have unintuitive results when combining elements with values greater than 1.0. The simplest way to get an add is to leave the Merge in Normal mode and set Alpha Gain to 0. Or you can use a ChannelBooleans, but remember to set Alpha to "Do nothing" or you wind up with an overdriven alpha channel, which is Bad.

I usually use a Crop rather than the Merge-over-Background method. Check the "keep centered" box so your element will be in the middle of the frame, and all of your blurs and other effects that clip to the DoD should work fine. And Transform values will be relative to your frame format instead of the element, which makes linking them with expressions or using Trackers easier.

One other thing: You can set the Blur's (and many other tools') Clipping Mode to None to avoid the problem, also, but there are so many advantages to reformatting that it's a better idea.

HA! Yes, I generally don't screen anything anymore either, it was just the first thing that popped into my head.

That's a good tip to use the crop with keep centered. I'll have to try that next time I'm in the situation.