Regarding the OP, there are two ways in which a widescreen film, be it 1.85:1 or 2.35:1, can be encoded on a dvd. The first method, and the method most often used in the early years of dvd, is letterboxing. In this format, the black bars at the top and bottom (of a 1.33:1 tv) are hard coded to the cd, which is to say, they are actually recorded as part of the picture. When a dvd of this type is played back on a conventional tv, you get small black bars if it is 1.85:1, and larger ones if it is 2.35:1. Because the black bars are part of the recorded image, fewer scan lines are actually used for the visible image.
The second method of presenting a movie widesreen on a dvd is anamorphic widescreen (which is unrelated to anamorphic filming or projection). A widescreen movie is stored on the dvd horizontally compressed, or it has the sides squeezed in to fit into the 1.33:1 storage format. On a conventional 1.33:1 tv, the dvd will electronically create the black bars by leaving out every fourth horizontal scan line, which decreases the resolution but restores the movie to it’s proper resolution.
Thus, on a 1.33 tv, an anamorphic widescreen dvd and a letterbox dvd will look identical, with black bars at the top and bottom, and the same number of scan lines used to display the picture. Thus, there is no advantage to anamorphic dvd’s on a conventional tv (with the exception of a small number of sets that do the ‘anamorphic squeeze’, by vertically compressing the sceen instead of leaving out scan lines, but these are rare).
On a 16:9 tv, things work differently, and this is where you get the benefits of anamorphic recording and playback. A movie filmed at 1.85 is filmed on standard 1.33:1 film, and for playback in the theater the top and bottom portions of the film frame are matted out, resulting in the widescreen image you see on the film. For dvd, only this middle “safe” portion of the film frame is recorded to the dvd, and it is horizontally squeezed into the 1.33:1 shape of a conventional tv. When the dvd player is hooked up to a 16:9 tv and fed an anamorphic dvd, it horizontally expands the compressed image to the full width of the tv. The result is that all of the scan lines are used to display the image instead of every fourth one being deleted, resulting in an image that has 1/3 more detail.
A letterboxed dvd, one that isn’t recorded anamorphically, has the black bars recorded as part of the image. Instead of stretching the image horisontally, it needs to be zoomed to fill a 16x9 tv. If the dvd is properly encoded and the dvd player and tv set are both set up right, this will be done automatically, but because fewer scan lines are filling the screen, the image quality can suffer a little to a lot. If the dvd isn’t properly flagged as non-anamorphic widesreen, you get either a window boxed picture (black bars on top, bottom, and the sides) or a picture that is incorrectly stretched horizontally, making everyone look too fat. This is easily compensated by selecting the zoom aspect on the tv, which will fill the screen with the image, but, as I said before, a lower resolution image.
A movie that is filmed at 2:20:1 or higher is filmed anamorphically (unrelated to anamorphic dvd’s), using a “fisheye” lens to horizontally squeeze a very widescreen image onto the 35mm film frame, and a matching lens on the projector is used to expand it in the theater. When these are recorded onto a dvd, most of what was described above for 1.85 images still applies, but now the anamorphic image is both horizontally compressed and has black bars encoded at the top and bottom. When the movie is expanded by the tv, the black bars remain, but they are much smaller than on a conventional tv. Letterboxed 2.35:1 movies are handled the same way as described above.
Gladiator and Shawshank are both anamorphic dvd’s. The key words to look for on the box are either “anamorphic” or, more commonly, “enhanced for 16 x 9 tv’s”, which means the same thing. If you try to play a widescreen dvd that’s not anamorphic (say, From Dusk Til Dawn), and it doesn’t display properly (there are a lot of factors involved here that affect this), all you have to do is use your tv remote and change the aspect from “full” to “zoom” and the picture should fill your screen, but without any increase in resolution. You can also use 4:3 mode, which will result in a windowboxed picture, which can look better in some cases. If your tv is an RPTV, you should ALWAYS watch such movies is zoom mode, never windowboxed, which can cause uneven wear. If you have a tube tv, it’s a matter of taste, the uneven wear is negligible.