Tech post – Why 1080p might actually be 1080i

By | 31st July 2017

Some 1080p devices such as camcorders might not send true 1080p signals via HDMI or HD-SDI. Instead they could send a 1080i signal containing progressive scan images. This is called 1080PsF (progressive segmented frame) but may not be labelled as such.

The reason for using this method of delivering progressive scan images is to maintain compatibility with earlier equipment designed to work with interlaced signals.

When a camera is set to 1080p it’s not always clear just by looking in the menu that the output from the  HD-SDI or HDMI connector may actually be sending 1080Psf.

Panasonic describe 1080PsF output in the manual of one of their cameras as follows –

In this case 1080/25p (over 50i) means the same thing as 1080/25PsF.

1080p and 1080i with computers and tablets

Many computers and tablets have HDMI outputs. When set to 1920x1080p these tend to be true progressive scan 1080p. This will usually work with a TV or computer screen but may not send a valid signal to a vision mixer, such as a Blackmagic Television Studio that might only be capable of handling 1080i signal.

If you have the right video card drivers with more advanced control of the HDMI output then you may be able to force the HDMI output of a computer to be true 1080i. Otherwise you may need to route the computer signal through a scaler to convert it to 1080i.

Tablets such as iPads differ in their capabilities. Older iPads may be limited to lower resolutions. Newer units will send 1080p but not 1080i. There are workarounds available using either a scaler or an Apple TV device and Airplay Mirroring. Just be aware that the older Apple TV devices are no longer supported.

Mixing 1080i and 1080p might not work

Some vision mixers include a scaler on every input. That means you can hook up any mixture of 720p, 1080i and 1080p – perhaps even 4k signals without a problem. However, there are some current devices that won’t work unless all the inputs are the same.

Blackmagic Web Presenter

The Blackmagic Design Web Presenter has both HDMI and HD-SDI. It will take any signal up to 4k and provides clean switching between the two inputs provided that the signals for both inputs are the same.

If you inadvertently connect 1080p and 1080PsF then the device will not provide a clean switch or mix. You may see a dip to black or other glitches.

Be aware that some devices will do a digital handshake to auto detect what signal the connected display is capable of receiving and adjust its own output to match. While this is helpful with a display it may not work with a vision mixer. Again a scaler may be needed to ensure compatibility.

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