I do not give myself much hope with opening a 301 MiB Gerber file.
Just out of curiosity (and against better judgement) I did try to open it in GerbView. Which resulted in me resetting my PC 23 minutes later.
I have a 12 year old Dualcore with a measely 4GB of ram.
Opening the file in Geany (my text editor) is a nice stress test, and I can even scroll though the 15 million lines of text without effort.
Files of this size often are badly formed, for example with excessive small unviewable details or even blunt file errors. I do not know if this is true in this case, but I do see repetition of coordinates for example:
lines 815910 and 815911 are the same, and I see this throughout the file.
The 2nd block (starting at line 815907) is a square with the end point the same as the beginning, but i’m not sure what the repetition of the coordinates on those other lines signify.
After that, I took the first 5000 lines of F.Mask, put it in a separate file and opened it in GerbView. I see 9 concentric circles and some small stuff in the lower right corner.
This handfull of pixels is 100kiB of the file.
Each pixel seems to be a square polygon which quite confirmes my suspicions of an extremely inefficient way of doing things.
There must be much better ways to import the same artwork with higher quality and less filesize into Pcbnew?
How repetitive is your border pattern?
If it’s highly repetitive, then re-tracing a bit of it in a vector format and making an array out of it seems like a good idea.
How did you make the artwork? What tools did you use to convert?
Are you aware of svg2shenzhen?
Dumping big bitmaps into a vector program is almost a recipe for a disaster waiting to happen. Even if you manage to make it with KiCad, I would not be surprised if a PCB manufacturer refuses to try to make it.