Change resolution CC problem

Hi,
i am working on very huge files (18 000 x 5 000) and i can't do anything about this. But i have to do the color correction on this file.
Is there any possibility to resize it in fusion for 1 800 x 500 then do the color correction then resize it to the orginal size and don't loose the quality of a original image?
I can't work with original resolution because it make my computer slooooooooooow. So i am looking for a solution how to work on a smaller reoslution and then scale all the effects to the higher resolution. How i should plan the flow?
I've tried resize footage to smaller, add effects, resize to original but the resolution of the original footage is then really really bad, how to do this so? is it possible?

Thank for any answers

If you're only doing color correction, working on a lower resolution is definitely a good idea.
You can either turn on Proxy Mode inside Fusion and do the resizing on the fly, or you can - as you suggest - work with an 1800 x 500 file and then, when you're satisfied with the result, replace the loader with the original resolution and let it render slowly. On the other hand 18000 x 5000 are indeed huge files, so it will make any computer and/or software run slow.

There is a field in the Loader for a Proxy image. Fusion will use that image as long as the Prx button is on, but it will always render using the main file. That gives you the ability to use a fast loading proxy image without needing to worry about changing out the Loader at render time.

Most tools are resolution-agnostic and won't care if you're working on something that is 1/10th scale. The exceptions are Filter, Custom Filter, Rank, and the Particles system. The former operate at the level of discrete pixels, so their results will change in proxy mode--they'll be stronger with Proxy turned on. The particles usually appear as though a different random seed was used.

Blurs and sharpening may be difficult to evaluate in proxy mode since the resolution is so much lower, but if you have a critical blur to adjust, you can always disable Proxy temporarily to dial in that specific effect.

Other tools that might give problems are anything that deals with screen-space vectors: Optical flow, vector motion blur, and stereo disparity. I'm not sure how those interact with proxy mode, but I suspect that they'll act similarly to the filters.

Film Grain might also appear differently in proxy mode. But usually you'd want to tune your grain with the full-resolution image, anyway.

Another item in the toolbox you'll want to use extensively is the Region of Interest (RoI) button, which allows you to only render a portion of the image. That can save quite a lot of time. Like Proxy mode, RoI is ignored when you render your final image.

Thanks for all information, they will help a lot.