Originally Posted by Woppet
Wrong. "Pillarboxing" only refers to thick bars when the image is academy ratio (1.37:1 or narrower), not matted. A film matted at 1.66:1 would be "windowboxed" (A Clockwork Orange) and a 1.37:1 with black bars on all four sides would be pictureboxed (Criterion academy ratio SD DVD's).
First off, when discussing specific aspect ratios and how they're presented, it's important to note what it's being presented on
. A 1.37:1 film is going to be presented a different way on a 35mm print for theatrical screening than it is going to presented on a Blu-ray for home video.
In general though, the terms letterboxing, pillarboxing, windowboxing and pictureboxing refer to the placement of any matting (i.e "black bars") on the media. Letterboxing is well known as horizontal matting on the top and bottom when the image is wider than the media. Pillarboxing is less known, but is becoming more common, and is the vertical matting on the sides when an image is narrower than the media. Windowboxing and Pictureboxing are interchangeable terms, both meaning when there's matting on all four sides of the image.
For a Blu-ray displayed on a 16:9 HDTV, any aspect ratio narrower than 1.77:1 (like 1.66:1, 1.37:1 and 1.33:1) will have to be pillarboxed to retain the correct image. For wider aspect ratios (like scope 2.35:1 or 2.40:1, or even 1.85:1), they have to be letterboxed. There is the potential for any of these aspect ratios (even 1.77:1) to be windowboxed if either transferred incorrectly or done deliberately to offset overscan.
For DVDs, it's more complicated due to the anamorphic enhancement option, and whether you're viewing on a 4:3 or 16:9 TV. A 1.66:1 film could be letterboxed (non-anamorphic, 4:3 TV), pillarboxed (anamorphic, 16:9 TV), or windowboxed (non-anamorphic on a 16:9, or anamorphic on a 4:3). As pointed out, a 1.37 film on a non-anamorphic DVD on a 4:3 TV could be windowboxed to counter overscan (which might not even be noticeable if the windowboxing is equal to or less than the amount of overscan on the TV).
For film, it's also complicated, but for different reasons. To go back to DeeF's question, nowadays a print of Barry Lyndon could be made that places a pillarboxed 1.66:1 image into the normally 1.85:1 viewing area, which is already letterboxed from the full 1.37:1 film frame, making the resultant image windowboxed in the full film frame. As Stephen_J_H pointed out, some 1.37:1 films are released this way due to limitations in modern film projection equipment. It's not ideal, however, since a 1.66:1 image fits best letterboxed into the 1.37:1 film frame, giving the most film resolution for the image.