A LQ episode IV publicity still despite being 600pix in height I managed to successfully get it to 2880, as I have found from experience upping the DPI seems to be the key, in this case 72 up to 800. As well as the dpi I used jpeg artefact removal brightness, contrast & clarity tools; I also added a new background layer balancing the grain between the 2 layers with vignette to finish off.
CHECK OUT MY STAR WARS GALLERY FOR MANY MORE RESTORATIONS/CONVERSIONS [link]
UPDATE I felt the picture need something more so I added a hint of paper texture, I liked the effect so kept it.
To Download left click to get full size then right click & save the image.