Resolution Misconceptions

I keep on finding the claim that progressive scan video necessarily gives a high resolution than interlaced video. For example, take this from

HDTV signals broadcast at 60 Hz, the standard for broadcast television, vary in what scanning format is used. The highest resolution format (1,920 x 1,080) is presented using interlaced scanning while the 1,280 by 720 format uses progressive scanning. Thus, the 1,280 by 720 format presents a complete 921,600 pixels 60 times per second. However, the 1,920 by 1,080 format presents only half of its total resolution every 1/60th of a second (1,036,800 pixels 60 times per second or 2,073,600 pixels 30 times per second). In essence, then, at a 60 Hz refresh rate, the true resolution of the two HDTV formats (what is presented every 1/60th of a second) is very similar.

This is true only in the case of material sourced from a progressive scan video recorder. It is not true with film-sourced movies. These are filmed at 24 frames per second. Progressive scan transmission at 50 hertz involves repeating every single telecined line twice. It’s a bit more complicated in 60 hertz countries since each line is shown 2.5 times. The ‘resolution’ in the sense of the amount of data carried by a progressive scan system is higher than the interlaced version, for sure. But the ‘resolution’ as used in common parlance — the amount of picture detail you see on screen — is, in the case of film sourced material (ie. virtually all movies), identical in the progressive scan and interlaced versions. It’s just that the progressive scan version carries a huge amount of redundancy.

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