vertical resolution

[quickfamily]

Hi,

This is really a capture question but it is such a newbie question I dare not put it in the capture forum.

1) The broadcast standard for PAL is 625 lines of resolution so why does SVCD work at 576 lines? What happens to the extra lines during capturing, do they just get thrown away?

2) Does my video camera (regular Hi-8 composite signal) output at 625 lines or something less than that.

Thanks

Andy

[kinneera]

The other lines are used for non-video data, the most well-known example being closed captioning.

[Anonymous65]

You're confusing "horizontal resolution" and the "number of scan lines".
PAL has 2 fields per frame, 312.5 scanlines per field, or 625 scan lines per frame. There are two fields per frame. PAL also has 25 frames per second. All the above data is set in stone, it is how a PAL TV-set makes or draws the TV picture on the picture tube. So, one PAL frame consists of 625 horizontal lines stacked ontop each other. From top to bottom of the screen there are 625 lines, OR the vertical resolution is 625 pixels. Since many of the lines just are black, or transmit sync signals or other non-image ratated data, the active number of picture lines in PAL is 576. This is why when you capture both fields in PAL the vertical resolution is always 576 pixels, and half of that, 288 in single-field mode, like for VCD captures. If the video is ever going to be displayed on a TV-set, you want to keep these vertical resolutions and not deviate from those numbers. If you do, you will end up with a non-standard PAL signal.

Now, for horizontal resolution. The quality of VCR's, TV monitors and other video devices are often meassured in "horizontal lines of resolution". In a nut shell, it basically means how many vertical black and while lines can you put horizontally (in 1 inch of display). Full PAL video has a resolution of about 500 lines. A VHS VCR can do about 250 lines, about half that of full PAL. Hi-8 might claim 400 lines of resolution. However, it's not so simple to say that the horizontal lines of resolution equals horizontal pixels!!! There are complex forumals for calculating the reslationship. But, VHS VCR has about 350 horizontal pixels, which is about 250 lines of resolution. Yes, I wish it was simpler, but it's not