What does 60 fields per second mean compared to 60 frames per second or 30 frames per second?

Question

i am looking to but a camcorder and upon reading reviews i do not know what 60 field per second mean

anyine know what it mans?

thanks tom =]

Answer 1

Tom,

60 frames per a second actually means 60 fields per a second.  60 fields automatically converts to 30 frames when viewed on your television.  In effect, 60 fields is the same as 30 frames which is why you often see this: 60i/30p when discussing frame rates.

Television video was originally developed to display at 30 frames per a second.  Television cameras originally recorded at the same 30fs rate.  Each of the 30 frames were progressive and carried every line of television pixels; which became known as 30p.

The problem is that at the time this was developed, radio technology was not broadband.  Radio technology was still being explored, so the full 30p could not be sent from the broadcasting station to you television fast enough to make it work properly.  Each of the 30p frames had too much data for the early broadcasting systems.

Sony came to the rescue by helping RCA and several companies develop interlacing video.  This allowed each of the 30p frames to be broken into to interlacing fields.  Every two fields are paired - with one odd (all the odd lines in the frame) and one even (all the even lines in the frame).  This allows all of the pixels of one frame to be broken into two similar sets of data.  30 frames became 60 fields.

Television cameras would record at 30p and the broadcast station or truck would break that signal down to 60 interlaced fields per a second or 60i.  60i can be broadcast more easily and much faster.   Your television recombines the 60 interlaced fields a second to create the 30fps video you see.  Soon Sony developed cameras that recorded directly to 60i which allowed broadcast companies to save time and money by skipping the breakdown step of converting 30p to 60i.  Sony even creates interlaced television which also skips the recombining step in the television.

The reason television is going all digital is to eliminate this conversion, or if it is needed, the conversion is automatically done behind the scenes without the need for human intervention.  Most camcorders come out of the box at the 60i settings.  Many camcorders will now allow the user to change this setting to meet their needs.  All of the newer HD televisions will accept and display signals from all of the common frame rates, 60i, 30p, and even 24p without the need for any converting of the signal before it reaches the TV.

Sony still uses interlaced technology not only because it is faster, but also because it shows movement very similar to the way the human eyes views movement.  The only problem with interlaced video is that there is no single solid frame.  This causes problems if one needs to work with singe frames or freeze frame video for analysis (such as sports reviews or evidence needs).  Full progressive 30 frame video is used for these situations.

* Now that you know all this, understand that 60i is not the same as 60p - in other words, 60 fields is not the same as 60 frames.  60 interlaced frames is used to create the standard 30p television video.  60 progressive frames is a high speed setting used to record high speed movement.  The movement is seen at half speed when viewed at 30fps.

Answer 2

NTSC displays 30 pictures (frames) per second*.  Each frame of the TV picture is made up of 2 interlaced fields - one has the odd numbered lines, the other has the even numbered ones.  60 fields/sec is the same as 30 frames/sec.  

* 29.97 to be accurate!