Left: digitised VHS source. Right: colour boosted in video editor.
Having completed my video about Memphis furniture [link], I am confident I have made a well-structured piece of television with good use of archive material, but I also learned how terrible the Video Home System (VHS) really was.
Having decided to include a fake advertisement break that reflected the influence of Memphis design, I realised that the recordings I used literally paled in comparison to my photographs of the real-life furniture. I already needed to boost the colour of the Weetabix ad I used, using a different VHS copy of it for reference, having being unable to find a copy that was higher in resolution and also not muddy in colour, but then I realised the colour of Warninks advocaat is yellow, not cream, and the swimming pool ladder in the Kitekat ad had to be brighter to match the more obvious influences in the colours and patterns used.
This is not a case of my digital photographs versus (the digital sample of) an analogue tape, the relative age of the tape, or the decline in quality of the recording over time, but more the technical limitations of the VHS format that have largely been overcome by the switch to digital formats, through no longer being constrained by a physical form.
On a 12.5mm-wide VHS tape, the top 0.65mm is taken up with one or two audio tracks, and the bottom 0.75mm is a control track used for synchronising recording and playback. The remaining 9mm is used for the picture, with a signal bandwidth of 3 MHz for luminance – the black-and-white signal that forms the picture - and a 400 kHz sub-signal for chrominance, reproducing the colour.
These numbers obviously doesn’t mean a lot by themselves, except that less space on video formats are reserved for colour signals because your eyes react more to changes in brightness, so a colour signal can be compressed more without much change in colour. However, the bandwidth of the original TV signal being recorded is much wider, with the PAL video standard using 5.5 MHz for luminance, and 4.43 MHz for chrominance, SECAM using 6 MHz and 4.43 MHz respectively, and NTSC, broadcasting a 525-line picture instead of 625 lines, using 4.2 MHz and 3.58 MHz respectively.
In order to fit your recording onto the tape, VHS has to throw much of the signal away in a manner that befits having tape only half an inch wide, playing at 1-1.5 inches per second – older professional, broadcast quality tape standards like 2-inch quadruplex, 1-inch Type C and U-Matic recorded a better quality by simply having more surface area to play with, running a wider tape more quickly to pick up as much information as possible. The later S-VHS standard increased the luminance signal recorded to 5.4 MHz, but kept the chrominance signal, and the speed of the tape, exactly the same.
While the picture quality of the contemporary Betamax format was better than VHS, the throwaway nature of TV advertisements often mean that the format that won out in the video format war often winds up as the archive format for those ads. One point of my video as to show how colourful 1980s design was but, without me doing anything with some of the images, another point would have been how our recordings of the decade washed out that colour.
No comments:
Post a Comment