anything visual is possible with image editors.  if you can display it on a screen, you can create it with an image editor.  it may take loads of time and skill, though.  is there anything in particular that you're interested in improving?

the big thing i notice you skipped is color correction.  the reason many images look more realistic in black and white is the lack of realism in the colors.  desaturation can help, but there are a lot of other aspects as well.

my gallery has varying levels of postwork.  let me know if there's any effect or some such that you'd like to know more about.