AfterDawn: Glossary

Scanline

Scanlines are the horizontal lines on analog TVs. While analog TVs don't have a specific horizontal Resolution, it has a vertical Resolution equal to the number of visible Scanlines, which are considered part of the Active Area of the TV. Additional scanlines are included in the video signal, but they're only present to provide the electron guns in a CRT display time to return to the top of the screen.

NTSC
NTSC video consists of 525 Scanlines, of which 486 are visible, and 480 are included in the Rec.601 standard used for most digital video. The Active Area of NTSC video, with respect to Rec.601 compliant Video Capture is 711x576 within a 720x480 Frame.

PAL
PAL video consists of 625 Scanlines, of which 576 are visible. All 576 Scanlines are included in the Rec.601 standard. The Active Area of PAL video, with respect to Rec.601 compliant Video Capture, is 702x576 within a 720x576 Frame.

Rec.601 Scanlines
For capture purposes, Rec.601 uses a line length longer than either NTSC or PAL, which is why the length (in pixels) of both NTSC and PAL video is less than 720. In the image below the black line in the middle is a Rec.601 line, while the red line above shows the relative length of a PAL Scanline, and the green line below shows a NTSC Scanline.



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Digital Video Fundamentals - Resolution and Aspect Ratio


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