about test pattern generator: short green line in test pattern

I believe the NTSC loaded by the clocked video output is 487 lines interlaced. Perhaps the short green line (7 pixels before the bottom?) is related to that

You cannot generate 487i with the Altera TPG but there is a workaround suggested in the user guide:

"The Test Pattern Generator cannot produce interlaced streams of pixel data with an

odd frame height. To create interlaced video streams where F0 fields are one line

higher than F1 fields, Altera recommends feeding Test Pattern Generator progressive

video output into the Interlacer MegaCore function."