Blu-Ray DVDs and Anamorphic Format

First off, a Blu-Ray disc is not a DVD, any more than a DVD is a CD. About the only thing they share is physical dimensions. Where CDs use an infra-red laser to read and record and DVDs use a red laser, Blu-Ray uses a blue-violet laser, which allows for a much smaller data spot on the disc and allows for vastly more data on a single disc.

As for anamorphic formatting, that refers to a photographic technique that compresses a widescreen image onto a standard 35mm theatrical film without letter box bars using a special lens, thus allowing somewhat better resolution by using more of the frame. When projected in a theater, a special projection lens is then used to decompress the image back to the theatrical widescreen format.

Anamorphic widescreen on the other hand is a digital compression technique which compresses a widescreen image into a standard 4:3 DVD frame, and which requires the proper codec to decompress the image.

It is worth pointing out that when the DVD was being developed, the 4:3 aspect ratio was still the standard for television and computer displays, and widescreen was primarily for theatrical use. Thus, the video resolution of DVD images is 760x576 (4:3) and special techniques are needed to adapt to 16:10 and 16:9 formats.

Since then, widescreen has come into widespread use and 4:3 is slowly disappearing. While I have been unable to find any specific information concerning the actual encoding of video format data, the maximum video resolution of Blu-Ray is 1920x1080, which is 16:9. This would seem to indicate that the native format is widescreen. It is worth noting that Blu-Ray discs use mpeg2 and mpeg4 codecs, whereas DVDs use mpeg1 and 2.

I suppose it's possible that a Blu-Ray disc might use a sort of reverse anamorphic compression to compress a 4:3 image into a 16:9 format, though I admit I don't really see the point.