Having obtained permission from BREMA, with whom we hold the joint copyright on the Test Card, Richard Russell at Kingswood has now re-created the 4x3 Test Card with the same re-scanned centre picture as was used in the widescreen Test Card W last year.
This Test Card also has the full range greyscale with pairs of flashing dots as used in Test Card W, and the green chrom/lum delay square in the top streak-box. These new features demanded a new ident letter. G was used for the original Philips electronic standby generator for TCF when that came from a slide-scanner, H was used for a studio line-up chart, I is a nasty letter - too easily confused with the number one, and so J was chosen.
The Test Card fills the full width of the digital active line, and is thus 18 pixels (about 2.5%) wider than the traditional analogue active line. The left and right arrow heads are therefore mirrored about the nominal edge position - just as was done on the original slide! These will not normally be seen, as the analogue blanking will cut off at the tips of the arrow-heads.
The extra white and magenta blocks at the sides are to aid checking the exact blanking position. The inside edges have the same 250ns risetime as the blanking edge should be, and when correctly blanked this will result in a 700mV raised cosine pulse, 423ns wide. (423ns is the 0-100% time of an edge whose 10-90% duration is 250ns.)
A final new feature is the addition of unique top and bottom lines which will immediately show (by their absence) if the signal has been passed through any processing that moves the picture up or down by a line. Line 23 has the Widescreen Signalling data on it, which is coded to specify a 4x3 signal. ("Video Index" has also been coded on line 11, and a range of standard ITS signals are also present in the field blanking.)
By altering a few parameters in his programme, Richard was easily able to create a 525 version of the Test Card. While essentially the same as the 625 version, the colour bars and blocks are the 75% type, as opposed to the 95% variety used on the 625 card. The frequency gratings are different to suit the lower NTSC bandwidth: 1.5, 2.5, 3.0, 3.5, 4.0, & 4.2 MHz. Finally, aside from the obvious "BBC 525 LINES" logo, the edge blanking check pulses have been changed to blocks of I and Q subcarrier. 525 NTSC has a wider active line than 625 PAL, and hence there are insufficient extra samples on the digital signal to sensibly make the blanking check pulses, so they were replaced by this standard NTSC check - 40 IRE units (286mV) of subcarrier at -57° and +33°, sitting on black.