PAL & NTSC & SECAM
PAL is the analog video format that was first introduced in 1967, developed by Walter Bruch in Germany. Short for “Phase Alternating Line”, PAL is used in most of Europe, Australia, and a few South American, African and Asian countries.
PAL was given its name because the color information on video signals is in reverse order with each line. The purpose for this is to correct any errors when the color signal is transmitted. Whereas NTSC receivers require manual correction for colour control, PAL corrects automatically. Though PAL was developed to handle any signal errors, such alternating of color data can cause picture grains to appear in extreme cases of error.
Video formats with 625 lines per frame and a 25 frame/second refresh rate are used with the PAL system. Each frame features two fields – one field holds all even lines, and the other frame holds all the odd lines. The transmission and display of the fields are done in a successive manner at 50 fields/second.
PAL comes in variations, including:
✓ PAL-M – a hybrid version used in Brazil combining PAL with 525 lines/60 Hz and NTSC
✓ PAL-N – featuring a narrow bandwidth, and used in Paraguay, Uruguay and Argentina
✓ PAL-I – used in the UK
✓ PAL-B/G – used in many European nations
✓ PAL-60 – used to display DVD or NTSC video on a PAL television set, featuring 59.94 fields/second
Used in the US, Canada, and even Japan, NTSC – an acronym for “National Television Standards Committee” – features 29.97 interlaced frames of video per second, with each frame containing 480 lines of vertical resolution. The addition of chrominance data on a 3.579545 MHz subcarrier replaced an older version of NTSC, which held onto compatibility with older black-and-white TV receivers.
At roughly 59.94Hz refresh frequency, a near flicker-free picture is displayed due to NTSC interlacing even-numbered scanlines in even-numbered fields, and odd-numbered scanlines in odd-numbered fields. Live TV broadcasts from decades ago were possible thanks to the ability to sync the power cycle and refresh rate. Capturing a frame of video to a film cell was easy with the synchronization of a film projector. Wave interference, which would show on screen as rolling bars, is prevented by matching up the refresh rate to the power source.
NTSC uses a chrominance subcarrier for color, with a frequency that needs to be kept in sync by the transmission of a colorburst signal before the line of video begins. Such colorburst has 8-10 modules of the subcarrier.
Conversion between NTSC with PAL or SECAM poses a challenge because the frame rate is different from each other. Video conversion equipment must estimate what’s in the intermediate frames that brings about artifacts. It’s easy for an expert to be able to spot a video that’s been converted from NTSC.
A total bandwidth of 6 MHz is what a transmitted NTSC TV channel takes up. In order to avoid interference between video and audio signals of adjacent channels, a guard band takes up the lowest 250 kHz of the channel, with the video signal being transmitted above the lower bound of the channel between 500 kHz and 5.45 MHz.
The sidebands of the video carrier are 4.2 MHz wide each, with only 750 kHz of the lower sideband being transmitted, as opposed to the whole upper sideband being transmitted. Above the video carrier is the color subcarrier, which is transmitted 3.579545 MHz above. The audio signal occupies the top 250 kHz of the channel, which permits compatibility with FM radio station audio signals between 88 and 108 MHz of the band. 4.5 MHz above the video carrier is the main audio carrier.
NTSC video is not exactly praised by video experts, who have nicknamed the acronym of the format to stand for “Never The Same Color”. The reasons for this are valid. First of all, The editing process of the video is made complicated due to the interlaced picture. Secondly, the color balance is often lost by the time the viewer sees the picture because of the degradation of the picture through radio interference. Lastly, NTSC’s 525 line resolution provides a poor quality image.
Short for Sequentiel Couleur avec Mémoire, which, translated from French, means “sequential color with memory”, SECAM was introduced back in 1967 in France where it is still in use today. Many Eastern European countries have also adopted SECAM.
Many believe that the French developed such a format on purpose to be incompatible with other formats as a means of protecting their TV equipment manufacturers. For this reason, Americans formulated a different meaning for the acronym, and dubbed SECAM as “System Essentially Contrary to the American Method”. Political reasons have also been believed to be part of the reason that Eastern European countries adopted SECAM as a means of preventing televisions from broadcasting anything outside the Iron Curtain.
SECAM is an analog TV format that encodes chrominance data through the use of frequency modulation. Lines of color data are stored through its memory, which avoids color artifacts.
Like the development and introduction of PAL, SECAM was developed as a means of countering the issues found with NTSC. The mechanism used with SECAM, however, differs from that used with PAL. The vertical color resolution is half of that of NTSC and PAL because of the alternate line transmission of the R-Y and B-Y data.
Three variants of SECAM exist today:
✓ French SECAM – in use in France and former French colonies
✓ MESECAM – in use in Middle East nations
✓ D-SECAM – used in Eastern European countries and Commonwealth of Independent States
It wasn’t easy to edit analog SECAM in its native form. For this reason, post-production was first done in PAL, then coded into SECAM.