01-18-2012 10:54 AM
I need to output a D-PAL video signal from PXI-5421,I have checked the documents and papers about PAL video signal,I also output a Standard PAL from NI Video generator and observed the signal on oscilloscope and VideoMaster，but I was confused on something：
1，PAL is Phase Alternate by line,as see in Rec. ITU-R BT.470-6 , you can see the Phase of chrominance subcarrier burst is alternate by line, but when I capture the signal from NI Video generator,I saw the Phase of chrominance subcarrier burst is same each two line on one field, as A A B B A A B B.let’s say that one frame have 625 line(two fields), the first field (1-312 line) is odd line and second field (313-615 line) is even line, in my understanding, in order to Alternate Phase by line, all of the Phase of chrominance subcarrier burst of first field must be A, and all of the Phase of chrominance subcarrier burst of second field must be B,so when it is show on the monitor, it shows A B A B A B, that’s real Phase Alternate by line,am I right?
2, How to output Eu *sin 2n fsc ? take color bars 100-75 for example, one line have 1280 points (20MS/s update rate),so I generate Eu = 0.493（B-Y）and subcarrier sine wave in 4433618.75Hz,it also have 1280 points, so I multiply sine wave and Eu directly by multiply function in Array form,in this way it is easy to understand the equation fsc= 283.7156 fH and the “4 frames & 8 fields repeated ”,but the result seems not correct, the phase of each color bar is not equal to the Colored vector illustration , but if I use sine wave start with 0 phase to multiply each color bar, then the result is very close to the Colored vector illustration, but how to understand “4 frame & 8 field repeated ” in this way?
As far as now, the signal I output is in wrong color bar and the odd line and even line flash quickly(5 times a second),see the picture below.The signal from NI video generator and my program. I will post my output waveform later.
I am appreciate for your time!
Solved! Go to Solution.
01-23-2012 09:36 AM
I get the point finally,the point is that the pahse between the chrominance subcarrier burst and Eu（or Ev）is relative,no asolutive.This post is colsed.
Thanks for your time!
01-23-2012 10:00 AM
1. The fact that a PAL frame has an odd number of lines, and because the subcarrier frequency is offset by 1/4 line to avoid vertical dot patterns artifacts, all adds up to the fact that eight complete fields (or 4 complete frames) are required to repeat a specific sample position. Explanation details found in "Video Demystified" book by "Keith Jack".
2. Difference in D-PAL and B/G-PAL only relates to the video bandwidth, audio carrier frequency and difference in I/F carrier frequencies, so for baseband video the NI Analog Video Generator can be used in Standard PAL mode.
Senior PSE, NI Multimedia products