I can't get why there are 625 lines in a PAL scanning system. I read R.R.Gulatti's standard book. In that there is a reason like:
"Suppose there are x lines in 1 field. Then for two field its 2x.For 1 field there are 292.5 scanning lines, so for 2 fields there are 2x=292.5*2=585 & 40 other lines ( because of merging effect and all).So 585+40=625."
I searched this on net but I could not find a proper reason for this. Also in Wikipedia there is no satisfactory answer.
I can't understand why there are 625 lines or odd lines in T.V. scanning. There is a sentence that mentions that "Scanning lines are always odd" but there is no reason given.
I got this solution is it right?
If you had an even number of lines then all lines must start at the beginning of the frame. If you have an odd number of lines then you will achieve the same resolution on the screen but the half line (the odd line), split in half with half at the start of the second frame and half at the end of the second frame allows for an extra line period in order to flyback vertically.
This "appears" to the human eye to be a better picture. If you think about the lines, they are all sloping so if you use full lines then for a full line scan the area at the top right and bottom left have no data in for a wider area than with half line second frame scan. The missing data area remains the same but is now split into two parts, immediately before the half line starts and at the end of the first half line.