In my disc database I have tick boxes to describe the presentation of the main feature of the disc. These include ‘Pan and Scan’, ‘Widescreen Anamorphic’, ‘Widescreen Non-anamorphic’ and ‘Widescreen cropped’. Pretty much by habit I’ve been ticking the ‘Widescreen Anamorphic’ box for Blu-ray discs, but it has recently occurred to me that Blu-ray discs aren’t anamorphic.
The word relates to a type of lens used more frequently in the 1950s in the early days of widescreen cinema. The film frames in most cinematographic formats retained the old 1.37:1 aspect ratio, and the obvious way to make them widescreen was just to shoot as usual, but with a mind to masking off the top and bottom of the frame for later cinema presentation.
However, that wasted a lot of the resolution of the film, so one alternative was to use a special anamorphic lens to distort the picture during photography. This squeezed the picture in sideways so that the widescreen picture could fit into a normal film frame. Then a lens to reverse the process was used at the cinema, stretching the picture sideways, so that its contents were restored to their correct proportions.
The term was carried over to DVD. The same frame was used both for ‘standard’ TV style video with a 1.33:1 aspect ratio, and for the various widescreen formats. ‘Anamorphic widescreen’ DVDs scaled the picture out sideways to achieve a 1.78:1 aspect ratio. The alternative was letterboxed widescreen, which wasted several tens of per cent of the pixels on the screen, due to the black bars at top and bottom.
As an aside, even 4:3 DVDs had to be scaled. Most NTSC DVDs were delivered with a picture resolution of 720 by 480 pixels, but for square pixels a horizontal resolution of only 640 pixels was appropriate. For PAL DVDs (720 by 576), a 4:3 picture needed 768 square pixels of display width, so these had to be scaled out in width a little.
But none of that applies to Blu-ray. The picture is held at 1,920 by 1,080 pixels, which is 16:9 format with square pixels. It is designed to be displayed on a a natively 16:9 display (preferably with a matching number of pixels), so there is no scaling at all. Blu-ray pictures are not anamorphic, even though they are commonly referred to as such on Blu-ray packaging.
Except for Constant-Image-Height fans. They distort the picture twice at the display stage — once electronically to scale upwards from 2.35:1 to 1.78:1 — and then immediately reverse the process optically with a reverse anamorphic lens which can be swung into place. The purpose of this is, I believe, to replicate the way the picture widens at the cinema for the wider formats. I just don’t like the picture damage this introduces.