24p v. 1080i

[JZASMM]

What are the major differences between shooting on a camera that supports 24p versus one that supports 1080i? Are there major differences in quality, etc?

 

[David Mullen ASC]

You have to separate capture mode from recording format. You can shoot 24P and record it to 24P/720, 24P/1080 or 60P/720 or 60i/1080. So I'm not sure what your question is.

Are you asking about 24P versus 60i photography? Or recording the 24P capture to 60i versus 24P or 60P?

 

[JZASMM]

I guess I want to know the difference between 24p and 60i photography... sorry, I don't really understand anything dealing with HD that well.

 

[element80]

There are two key differences. The first is interlaced vs progressive, and the second is the frame rate. Interlaced video (what the i stands for) divides each frame into two fields. One field of pixels in odd-numbered rows, and one of those in even. During playback of 60i footage, the monitor scans each field one at a time, sixty times per second. Progressive (what the p stands for) on the other hand, keeps each frame together, and scans each line of the frame in order, rather than breaking it into two fields. The frame rate tells how many frames the video has per second. With interlaced footage, you divide the number by 2 to get the frame rate, so 60i footage is 30 fps. 30 fps is the frame rate for NTSC video (the standard in the US). 24 fps is the frame rate of film. 24p is a video format created to better emulate the look of film because it has the same frame rate, and the progressive scanning looks more like film than interlacing.

 

[David Mullen ASC]

24P means the camera captures images as whole video frames, 24 times a second.

60i means that the camera captures images as fields containing every other line of video, two fields to make up a frame, 60 times per second (hence why 60i is also known as 30 frames per second, because there are two fields for every frame of video. But that's not the same thing as 30P, which means capturing 30 whole frames per second.)

When two fields are combined, since each was shot sequentially, one after the other, any moving object occupies a different spot in each field, so when two fields are combined, the whole frame shows a toothcomb effect along the edge of the movement.

With a film camera, the shutter is a spinning disk with a slice cut out to allow light to pass through, and usually it is a half-circle (180 degrees out of 360) so the shutter is open only 50% of the time. So at 24 fps, the shutter is closed for half of 1/24th of a second, so the exposure time is 1/48th of a second. The low frame rate of 24 fps, combined with the shutter being closed half the time, gives motion that unique strobey look we associate with film.

 

[JZASMM]

Thanks.

 

[Filmosity]

Also, you may want to know what 1080 and 720 refer to. Those numbers indicate how many horizontal lines are drawn on the screen. When you see 1080i, that means there are 1080 lines on the screen, but they're drawn on there in an interlaced mode. 1080p refers to the same thing, except all the lines are drawn in one sweep, or in progressive scan mode.

So, the number refers to the number of lines that make up the frame, and the letter denotes the scan mode (interlaced or progressive).