Electronics > Projects, Designs, and Technical Stuff
Why modern analog cameras still using TVL(Television-Line) as a spec?
zajusako:
Hi all.
I understand this value is from old line-scan cameras/TVs, so why modern CCD/CMOS based analog CCTV cameras still using TVL? And why don't that value equal the vertical pixel count?
Thank you.
tooki:
"Lines of resolution" is the granularity in the horizontal.
For example. NTSC is 525 scan lines, of which historically around 485 are actually visible (due to overscan), which is why we chose 480 in digital standards for SD.
The number of scan lines is fixed, as it is a fundamental characteristic of the analog signal format. So when we look at a stated spec like a standard VHS VCR having about 300 lines of resolution, it means that in each scan line, the VCR can resolve down to about 300 lines. But the key thing to remember is that it's analog, so there are no pixels. It's a continuous value within each line. Whether this signal originated in a vidicron tube or a CCD, the analog signal is still this analog signal.
dmills:
TV Lines is also a very useful measure when you look at a whole camera system, in particular with a modern HD or 4k chain, the glass on the front can be a significant limiting factor (particularly as you crank the iris open in low light conditions).
Just because my sensor can manage 3840 pixels or whatever does NOT mean that I can resolve that by the time the prism block & lens have done their thing.
Regards, Dan.
tuzakeyiwe:
--- Quote from: dmills on February 17, 2019, 09:38:33 pm ---TV Lines is also a very useful measure when you look at a whole camera system, in particular with a modern HD or 4k chain, the glass on the front can be a significant limiting factor (particularly as you crank the iris open in low light conditions).
Just because my sensor can manage 3840 pixels or whatever does NOT mean that I can resolve that by the time the prism block & lens have done their thing.
Regards, Dan.
--- End quote ---
CCTV camera bodies also have that spec, and this is a mystery for me for a long time...
videobruce:
The Chinese CCTV industry appears to use the resolution of the actual sensor, not what the final video output actually is. Which is why these grossly inflated numbers (typical marketing lies) come from. Mostly noticeable with old school analog cameras calming up to 800 lines when the NTSC limit is 480 (more or less as stated).
One look at these so-called hi-res cameras on a high res display (1080p or even a 720) clearly shows that is a lie.
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