If it's not a huge file don't expect to be able to enlarge "big" without pixelization. Raster art large enough to print at poster size will be quite a large file. Saving as an .eps doesn't make a small raster file scalable. It needs to be vector.It could be created at say 600 ppi at about 5" diameter so it's not a huge file and then saved as an EPS file. Then it could be enlarged almost as big as you need.
If it's not a huge file don't expect to be able to enlarge "big" without pixelization. Raster art large enough to print at poster size will be quite a large file. Saving as an .eps doesn't make a small raster file scalable. It needs to be vector.It could be created at say 600 ppi at about 5" diameter so it's not a huge file and then saved as an EPS file. Then it could be enlarged almost as big as you need.