Currently you are copying pixels and saving the default canvas, but you want image slices and save those. Also try to prevent magic numbers where possible, because this could lead to errors as a result of typos (such as the 1080 in your question) or out-of-bounds errors for smaller images. Try this...

Adapted Code

1. for(int f=0; f<1; f++) {
2.   String imageName = "loo" + nf(f+1,4) + ".bmp";
3.   PImage img = loadImage(imageName);
4.   for(int p=0; p<img.width; p++){
5.     PImage slice = img.get(p, 0, 1, img.height);
   
6.     String outName = "slice" + nf(f+1, 5) + "-" + nf(p, 5);
7.     slice.save(outName);
8.   }
9. }