1080p, 1080i, 720p, and other HD video topics

*Q1. What are 1080p, 1080i, 720p?*

A. To be completely accurate, display resolutions should include a framerate and display mode. Progressive video shows a complete picture (frame) each cycle. Interlaced video shows only the odd lines (one field) in one cycle, and the even lines (the other field) in the next cycle. This allows an apparently smooth motion but with half the required data rate.

Deinterlacing is some method of turning an interlaced signal into a progressive one. Fields may be combined into a complete frame, fields may be thrown out, or new lines can be interpolated between existing lines. Different methods of deinterlacing are used depending on the source, the output, and the desired frame rate.

The commonly discussed resolutions and rates are:
720p60: 1280x720 progressive, showing every line 60 times a second creating smooth video-like motion
1080i60: 1920x1080 interlaced, showing every other line 60 times a second creating smooth video-like motion
1080p30: 1920x1080 progressive, showing every line 30 times a second creating less smooth film-like motion
1080p24: 1920x1080 progressive, showing every line 24 times a second creating a less-smooth very film-like motion
1080p60: 1920x1080 progressive, showing every line 60 times a second creating a very smooth and complete picture; does not commonly exist

1080p60 would require twice the data rate of 1080i60, 1080p30, or 720p60. Eventually broadcast systems may be upgraded to allow this. Most people mean 1080p30 when they say 1080p. Almost all HD TV broadcasts are either 1080i60 or 720p60. Blu-ray discs are usually 720p60 or 1080p24, but might also by 1080i60. Consumer HD camcorders are usually 1080i60, but may have a 1080p30 or 1080p24 mode. 1080p60 camcorders are just appearing, but require special handling because of the extremely high data rate. Also, their footage could not be put onto a Blu-ray discs at its native resolution and rate, since Blu-ray does not support 1080p60.

*Q2. What is "Full HD"?*

A. Full HD is a marketing term that is useless; it implies that 1080p is "better" than anything else, without specifying whether it means 1080p30, 1080p60, or 1080p24. Also, what resolution and rate is "better" depends on the usage. Progressive video at 30 complete frames each second looks clean and film-like, but lacks the smooth motion that some want when viewing video. 1080i60 has the smoothness and realism of motion of video, but may show combing artifacts if not properly handled. 720p60 has both a clean picture and smooth, realistic motion but uses a smaller frame size. 1080p60 would be "best" if it existed, but there are very few consumer products that can film or display it. HD TV and Blu-ray do not support 1080p60. To say that some format is "more HD" or "full HD" is an inaccurate and useless oversimplification. Even 720x480 is considered HD if it is progressive (480p).

iMovie users may encounter the term "full" when importing video. Since iMovie transcodes most input formats to an appropriate format for editing, it gives the users the option to change the frame size at the same time to save on disk space. A full size import preserves the original dimensions of the video.

*Q3. But isn't my TV 1080p60?*

A. Yes, but it is doing a "bob" deinterlace, and creating a 1080p60 video from 1080i60 by interpolating the missing lines. Or it may be creating 1080p60 video from 1080p30 by interpolating frames between the existing ones. The same process is used to create a "120Hz" motion. None of the created information is actually in the source signal.

*Q4. Is progressive video better? Should I always deinterlace?*

A. No, it depends on the source and the usage. For some applications interlaced video at 60 fields per second (i60) looks best. For other applications progressive video at 30 frames per second (p30) looks best. Generally speaking the motion of i60 will look more realistic and video-like. Generally p30 or p24 will look less smooth, but more like film. The desired appearance and application determines the choice of frame rate and display mode.

This is the 1st version of this tip. It was submitted on Apr 24, 2010 by Jeremy Hansen.