The black bars on your screen are not a fault and not wasted pixels. They are what happens when a film's shape and your screen's shape do not match, and the only choice is what to give up: the edges of the picture, its proportions, or a strip of screen.

Three shapes, one screen

A modern TV is 16:9, which is the same as 1.78:1 (the width is 1.78 times the height). Films were shot in several shapes, and the common ones are these.

• About 1.37:1, the "Academy" shape. Nearly square, the shape of classics such as Casablanca. Early television used 4:3 (1.33:1), so these films fit old sets well and leave bars at the sides of a widescreen one.
• 1.85:1, "flat" widescreen. Used for many dramas and comedies, Pulp Fiction among them. It almost fills a 16:9 screen, about 96% of the height, so the bars are thin.
• About 2.39:1, "scope". The widest mainstream film shape, found on a lot of action and science fiction, Blade Runner 2049 among them. You will also see it written 2.35:1 or 2.40:1: early anamorphic prints were 2.35, and projection was adjusted in the early 1970s to roughly 2.39. On a 16:9 screen it uses about 74% of the height, so roughly a quarter of the panel is black.

Bars above and below are called letterboxing. Bars at the sides are pillarboxing. A small picture with bars on all four sides is windowboxing, and it usually means a source or setting is mismatched.

Try it: fit, zoom or stretch

Pick a film shape and a screen, then choose what your TV does about the mismatch. The picture is a simple drawing, a sun on a horizon, so you can see what each option does to it.

What each mode costs you

Fit keeps the whole picture in its original proportions and accepts the bars. It is the faithful choice, and on most sets it is called something like "Original", "Auto" or "Just scan", though names vary by brand.

Zoom to fill scales the picture until it fills the screen, which cuts off whatever overflows. For a scope film on a 16:9 TV that is about a quarter of the width, lost from the sides of every shot. The director framed the shot for the whole width.

Stretch pulls the picture to fit in both directions. Nothing is cropped, but every face and wheel is the wrong shape, and the drawing above shows it: the sun becomes an oval.

When the shape changes mid-film

Some films move between shapes on purpose. True IMAX film is about 1.43:1, and some releases use an expanded 1.90:1 for IMAX sequences, which is closer to what most digital IMAX screens show. One published account of The Dark Knight says the IMAX scenes were about 1.44:1 and the rest 2.40:1, and that the Blu-ray switches to a full 16:9 picture in those scenes while the DVD stays 2.40:1 throughout. The same source notes that Enchanted opens with a 1.85:1 animated prologue before widening to 2.40:1, so on a 16:9 screen the opening shows bars on all four sides.

So the bars can move during the film. That is the film changing shape, not your TV misbehaving.

Can you get rid of the bars?

Not without giving something up, because no single screen matches every film. People who care most about scope films sometimes use a projector with a 2.39:1 screen, where scope films fill the picture, but then 16:9 material shows bars at the sides. On a TV or projector whose blacks are weak, bars can look dark grey rather than black, and that is a contrast limit of the display rather than an aspect ratio problem. For a normal TV the practical advice is short: leave it on the fit setting, and let the bars be part of the picture.

Sources

Shapes, examples and percentages are from published guides, with the arithmetic checked against 16:9 = 1.78:1: Sound & Vision, "Aspect Ratio Oddities" and Custom Controls, "Movie Aspect Ratios Explained".