Explain TV Lines

Could someone explain to me what TV Lines mean when it comes to a camera? I was looking at various specification and came across how many TV Lines a camera has. A quick google search shows it’s also appears to be referred to as the lines of horizontal resolution. Based on that definition it says it’s essentially the number of columns in a picture.

I was looking at one camera that’s popular over in the US for outside broadcasts now - the Sony HDC-4300L which has 2000 horizontal lines at the center in 4K. Does that mean there are 2000 lines on either side of the center? Because that is significantly less than the 3840x2160 that’s expected in UHD.

I’ve seen it in other manufacturers for regular HD listing 1000 TV lines.

TV lines is basically terminology from the analogue days which has stuck around, when cameras and CRT's scanned a frame a line at a time.

Vertical lines are the number of lines which make up the picture from top to bottom, which in the digital world directly translates to the number of pixels vertically. For example full HD is 1080 lines.

Horizontal lines is slightly more complicated as they aren't really a thing, just terminology the camera manufacturers have come up with to express the horizontal bandwidth of a camera in the same way they express the vertical resolution, as if they were lines scanned from top to bottom. In the digital world this is the number of pixels horizontally.

Regarding the 'at the center' terminology, I'm afraid I'm not exactly sure what that means. Using your interpretation, if that does mean there is 2000 lines either side of the center, then its horizontal resolution would be 4000 pixels, higher than the output resolution for UHD. I'm not sure your interpretation is right however.

AIUI tv lines in horizontal terms are defined by the number of vertical black lines you could see on a white background at the limit of your system. To resolve 2000 black lines against white at the limit you'd need ~ 4000 pixels (4000 pixels alternating between white and black would let you resolve 2000 vertical lines)

This is obviously a gross simplification ignoring the fact that TV is based on samples, that you have to consider the MTF of your lens and optical sensor system etc. - but as a rule of thumb your TVL resolution is around half your horizontal sample count in an ideal system (assuming equal resolution 3-chip cameras) I think.

AIUI camera manufacturers quote the equivalent full-width resolution that you'd achieve for the performance of given areas - so if the centre of the camera sensor is quoted as 2000 TVL that's the effective resolution of the system at the sensor (if scaled to the full width), however chances are the performance at the edges of the sensor is reduced, so will have a lower TVL spec. It's effectively a way of saying that the centre is theoretically about as good as possible, but the edges degrade a bit.

Annoyingly this definition is at odds with the vertical line count figure - which is the total number of horizontal scanning lines.

Thanks. Sounds like it’s one of those things that has stuck around.

They say every days a school day and this certainly hits the mark there. I never knew about the digital version of TV lines. Thank you