[FIFA1966]

If anything between 1280 x 720 and 1920 x 1080 is 720p, then what resolution is 1080i?

[Chris Frost]

That's not quite right.... I presume you mean 1920x1080 is 1080p and not 720p as you wrote.

1080i is 1920x540 for the odd lines + 1920x540 for the even lines. When interlaced together the result is 1920x1080i. So it's half the horizontal resolution of 1080p. It's also half the bandwidth which is why it's the chosen res for Sky and most Freeview/Freesat HD transmissions.

[Nigel Goodwin]

Originally Posted by Chris Frost

That's not quite right.... I presume you mean 1920x1080 is 1080p and not 720p as you wrote.

I presume he means that anything between those two values is 720P?, which is utter nonsense - the resolution of the screen is what it is, it's not either 720P or 1080i/P, which are broadcast resolutions, not TV ones.

Most sets that aren't Full HD are 768 pixels, NOT 720.

1080i is 1920x540 for the odd lines + 1920x540 for the even lines. When interlaced together the result is 1920x1080i. So it's half the horizontal resolution of 1080p. It's also half the bandwidth which is why it's the chosen res for Sky and most Freeview/Freesat HD transmissions.

A highly misleading statement

Depending on the exact compression, and on very fast moving action only, the horizontal resolution 'could' be lower than 1080P, with the theoretical minimum being 540.

In practice the only way to tell the difference is by what the on-screen display tells you - I don't think anyone has ever claimed to be able to tell which is which just from watching it.

[chrisjr]

Originally Posted by Chris Frost

That's not quite right.... I presume you mean 1920x1080 is 1080p and not 720p as you wrote.

1080i is 1920x540 for the odd lines + 1920x540 for the even lines. When interlaced together the result is 1920x1080i. So it's half the horizontal resolution of 1080p. It's also half the bandwidth which is why it's the chosen res for Sky and most Freeview/Freesat HD transmissions.

At the same frame rate and the same number of bits per pixel 1080i and 1080p are identical in terms of the number of bits per second required.

[Gormond]

Originally Posted by chrisjr

At the same frame rate and the same number of bits per pixel 1080i and 1080p are identical in terms of the number of bits per second required.

My understanding is that broadcasting cameras capture at 1080p 25/30 frames per second then when broadcast this is converted to 1080i 50/60 fields per second. If there was no conversion to interlaced the bit rate would be identical, around 1 Gbit/s.

[Nigel Goodwin]

Originally Posted by Gormond

My understanding is that broadcasting cameras capture at 1080p 25/30 frames per second then when broadcast this is converted to 1080i 50/60 fields per second. If there was no conversion to interlaced the bit rate would be identical, around 1 Gbit/s.

You're rather ignoring the fact that both would be compressed

For uncompressed data the bit rate would be identical, for compression it depends entirely on the type and degree of compression used - either 'could' be slightly smaller, but they are unlikely to be identical.

[Gormond]

Originally Posted by Nigel Goodwin

You're rather ignoring the fact that both would be compressed

For uncompressed data the bit rate would be identical, for compression it depends entirely on the type and degree of compression used - either 'could' be slightly smaller, but they are unlikely to be identical.

I wasn't ignoring it but for the purpose of comparison they are the same, as neither are better than the other.

[chrisjr]

Originally Posted by Gormond

My understanding is that broadcasting cameras capture at 1080p 25/30 frames per second then when broadcast this is converted to 1080i 50/60 fields per second. If there was no conversion to interlaced the bit rate would be identical, around 1 Gbit/s.

The bit rate is identical whether you do progressive or interlaced for the same frame rate and bits per pixel.

Do the maths.

1920x1080x25 = 1920x540x50 = 51,840,000 pixels per second. Multiply that by the number of bits per pixel (probably 24) to get the final figure which is around 1Gb/s

The biggest determining factor on the actual transmission bandwidth is not whether it is i or p but how hard you make the encoder work to reduce the bitrate. It is entirely possible to transmit 1080i at a far higher bitrate than 1080p or vice versa. But if both are sourced from a 1920x1080 frame and the number of frames each second is the same then the raw source bitrate is identical.

[Chris Frost]

I think you'll all over-complicating the matter. It was quite a simple question, with one probably unintentional slip.

[grahamlthompson]

Originally Posted by FIFA1966

If anything between 1280 x 720 and 1920 x 1080 is 720p, then what resolution is 1080i?

1280 x 720 progressive is 720p

1440 x 1080 or 1920 x 1080 interlaced is 1080i.

The last number indicating the number of lines the first can vary. 576i has a number of variations with the highest being 720 x 576.


Don't confuse signal resolution with the display resolution you view the video on.