Explanation Needed...VFR and Fields vs. Frames

[DMcCann]

I am trying to understand HD filmmaking a little better... 3 questions...

1 - Does 1080x720 mean lines of resolution or dpi (dots per inch)?

2- When shooting @ 60fps, more information is collected per frame, correct? Then why not shoot all footage at 60fps if there is more information and better quality?

3- Does anyone have a good explanation for the differences between frames and fields? If we are recording at 24fps, does that mean that there are 60 fields recorded per frame?

Generic questions, but sometimes a basic refresher can be very useful as this digital world can sometimes be a little overwhelming. Anything helps, thanx

[Filmbuff28]

1. 1080 and 720 refer to the horizontal lines of resolution, as opposed to the vertical line count which is usually 1280 for 720 and 1440 or 1920 for 1080.

2. When someone shoots at 60fps they do not increase the amount of information per frame. The amount per second, yes but not the amount per frame. A frame is a frame not matter what rate it is shot at. There is no difference in quality between a frame from 60fps or a frame at 2fps as long as the format does not change. I'm not sure if that is what you meant to say in the question but just in case. And the reason why most people don't record in 60fps is because most people are looking to achieve a certain "look", usual a "film look" which means 24fps, just like the movies. 30fps looks "digital" and ca be used for a "tv" look. 60fps is usually used to have more frames per second, like what is seen sometimes on football in particular the slow motion replays. But remember as mentioned above that a frame shot at 2fps, 24fps, 60fps, whatever, will yield the same amount of info and quality as any other frame so long as they are shot in the same format.

3. This last one is a bit tougher to explain with text but I will try. first, a frame is a complete and independent image much like a photo. It can stand alone on its own. A field is a piece of a frame kinda. If you shoot in 60i there are not actual frames every 1/60th of a second, half of a frame is recorded (every odd line lets say) and then the next 1/60th of a second the second half of the frame is recorded this time the even lines. But when 60i footage is imported, say to final cut, those odd and even frames are put together in a 30fps timeline. The lines can be easily noticed during any movement in the frame, in particular fast movement. Like a ball bouncing, you will probably be able to see both combined fields and the ball will look split up like a shredder went to work on it. It's complicated and I hope someone can explain it better but that's what I got and I hope it helps some of you.

At least number one was easy! Feel free to fill any gaps or reconstruct if I have been misinformed.

JP

[John Froton]

1 - Does 1080x720 mean lines of resolution or dpi (dots per inch)?

Neither. 1920x1080 and 1280x720 are frame sizes measured by pixels (width by height) 1080 and 720 refers to the vertical pixel resolution of those screen sizes.


2- When shooting @ 60fps, more information is collected per frame, correct? Then why not shoot all footage at 60fps if there is more information and better quality?

Shooting more frames per second does not increase the resolution of each frame (example 1280x720) but rather changes the temporal feel by adding more frames per second. The image quality will not improve but the sense of motion will become smoother. At 60 fps video looks much more like smooth video than cinematic film with it's slower framerate of 24 fps.


3- Does anyone have a good explanation for the differences between frames and fields? If we are recording at 24fps, does that mean that there are 60 fields recorded per frame?

Fields are just the way that the NTSC video signal handles and displays frames. It would be great if NTSC could show you a complete picture for every frame grabbed as a still picture, but it can't. It divides the image into many scan lines and then throws the EVEN scan lines into one field and the ODD scan lines into a second field. This way it can get away with displaying only 50% of the image at any given moment in order conserve in bandwidth and display data. Every frame in NTSC video is made up of 2 fields, one field is all of the ODD scan lines and the other field is all of the EVEN scan lines.

Progressive video is video that is scanned and/or reconstituted into full frames and it yields much better looking video than video with fields (interlaced video)

I hope this helps ;)

[David Jimerson]

To be clear, the PAL standard is interlaced, too, at 50 fields per second.