405-LINE WAVEFORM

This is just an example of the timing. Different books give different figures !

The following discription describes how the video signal line is extracted from a bitmap. You can skip this if you aren't interested how the software works.

In this project we shall attempt to map a bitmap (.BMP, .GIF, whatever) to the relevent picture line. By comparing a bitmap (B) with the interlaced TV picture (A), we can see that bitmap line 1 (L1) is TV line O1, L2 is E2, L3 is O2, L4 is E2, etc. In turn we can campare fig2 (A) with fig1 and get a mapping between the bitmap line and the line number of the 405 line signal :-

Bitmap Line(Fig2B)	TV Screen (Fig2A)	Signal Line (Fig1)
L1	O1	216
L2	E1	14
L3	O2	217
L4	E2	15
L5	O3	218
|	|	|
L377	O189	404
L378	E189	202

We can now describe each signal line in terms of a source bitmap and sync lines :-

WAVEFORM LINE	DESCRIPTION
0..3	Pairs of vertical sync pulses
4..13	Normal sync but with video at black level
14	Line 2 of bitmap
15	Line 4 of bitmap
|	|
201	Line 376 of bitmap
202	First half of bitmap line 378 plus one vertical sync
203..205	Pairs of verical sync pulses
206	One vertical sync foolowed by second half of bitmap line 1
207	Line 3 of bitmap
208	Line 5 of bitmap
|	|
403	Line 375 of bitmap
404	Line 377 of bitmap

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