Picture of ESB:
https://pbs.twimg.com/media/CpxG4GzVYAAa-5N.jpg
Here’s the Blu-ray:
http://caps.pictures/198/0-starwars5/full/star-wars5-movie-screencaps.com-1647.jpg
And here’s the new image compared to the Grindhouse:
http://screenshotcomparison.com/comparison/188119
As you can see, the matte lines are gone, but it’s also a warmed-up image. I would guess that either they just adjusted the color of the 2011 Blu-ray or it’s a new scan with the elements recomposited. A third option would be that they scanned a '97 release print, which would explain the additional grain that Tack reported.