Here's what's happening:
- During each second of 1080i video, you're seeing 60 frames.
- However, each frame does not contain the whole picture. Bear with me here.
- With 1920 x 1080 resolution on a TV, there are 1,080 rows of pixels going across the screen (those rows are 1,920 pixels long, hence the 1,920 x 1,080 number used to describe the resolution).
- Each frame alternates between flashing an odd row of pixels, which covers 540 – or half – of the 1,080 rows of pixels on a 1080 TV. Once the frame with the odd row of pixels has been flashed, the next frame flashes the remaining 540 even rows of pixels.
- The odd and even frames flash so rapidly – 30 times per second each – that it looks like a complete picture.