So if you can messure the WDR in dB for fixed cameras (60dB, 120 dB) and for PTZ you use the x (128x), i wanted to know what is the direct relation between them if any?
Subscriber Discussion
What's The Difference Between WDR In PTZs And Fixed Cameras?
MI
Matt Ion
Mar 30, 2015Terms like "128x" in PTZs refer to the zoom factor, not the dynamic range of the image; there is ZERO correlation between the two terms.
At 128x they're probably including digital zoom. A "typical" optical zoom might be something like 20X, which could indicate a lens that ranges between 3mm and 60mm, or from 6mm to 120mm - strictly a ratio of longest to shortest focal length.
UM
Undisclosed Manufacturer #1
Mar 30, 2015Some manufacturers will state their WDR is 128x. Meaning the different between the dark and light areas are 128x compared to a "conventional camera".
"Panasonic Super Dynamic III technology delivers 128x (NTSC) wider dynamic range compared to conventional cameras." https://security.panasonic.com/pss/security/products/pdf/WV-CW970CW960_2A-012CA.pdf
This is falling out of favor, because it is hard to measure vs. a dB rating. Also, the next manufacturer can then make a camera that delivers 129x WDR and is "better performance".
It shouldn't have anything to do with PTZ vs fixed cameras. Just how some manufacturers state their WDR performance.
MI
Matt Ion
Mar 30, 2015Hmm, good to know - I've never seen it expressed that way. Seems particularly silly to use that method for PTZs though, where zoom factor is one of THE relavant specs.
Well in that case the conversion should be fairly simple - dB is a logarithmic scale and in most cases, 3dB equals a doubling or halving of levels, and 10dB is a factor of 10.
Given that, 3dB = 2x, 6dB = 4x, 9dB = 8x, 12dB = 16x, 15dB = 32x, 18dB = 64x, and 21dB = 128x.
JH
John Honovich
Mar 30, 2015In general, WDR ratings should be taken with a grain of salt, as they are self-assigned, whether it is measured in dBs or 'x's.
MI
Matt Ion
Mar 31, 2015Yes, well, nebulous self-defined specs with no industry standardization, let alone oversight, are common in all realms of technology :)
AA
Ahmed Aziz
Mar 31, 2015Even if they are self-assigned, can we be 100% sure that there is no direct correlation between the dB and 'x's ?
JH
John Honovich
Mar 31, 2015Statistically there is a positive correlation overall, but how does that help you when you are trying to compare 2 individual cameras?
Let's say A says they are 130 and B says they are 110. Are you going to say 'odds are A is better' let's go with that?
How do you know A is not simply more aggressive in inflating their self-appointed rating?
MI
Matt Ion
Apr 01, 2015Let's say A says they are 130 and B says they are 110. Are you going to say 'odds are A is better' let's go with that?
A better way to illustrate this might be looking at 'x' as a zoom factor. A PTZ that states 20x optical zoom could be 3-60mm, or 10-200mm... all '20x' tells you is the ratio of widest to tightest shot for that specific camera. This MAY give you an idea of the camera's versatility, and something to partially compare price ranges on.
However, if you're trying to decide whether camera A or camera B will give you the FOV you need, '20x' is largely useless as a spec - for that you need to know the actual focal lengths, or at least one of them.
U
Undisclosed #2
Apr 01, 2015I don't see the correlation. Even though it's true that zoom factor alone doesn't give you all the information you might need, it's not like the manufacturer is hiding the actual focal length range from you. Any camera maker of any reputation will list it on their spec sheet. And once you know the focal length you can verify they are not lying about the zoom factor. Because the focal length yields the zoom factor.
But what is the underlying thing that yields the dynamic range number? Nothing I know of.
Moreover, if you were to buy camera A only knowing that it had 10x more zoom, even if you were disappointed in the actual focal length, it would still have 10x more zoom, right?
But with dynamic range, since different mfrs claim different methods of measurement, you are not guaranteed to get the camera with greater dynamic ranger just because the spec says so. Unlike zoom factor.
MI
Matt Ion
Apr 01, 2015Even though it's true that zoom factor alone doesn't give you all the information you might need, it's not like the manufacturer is hiding the actual focal length range from you. Any camera maker of any reputation will list it on their spec sheet.
That's true; my point was merely that if FOV is the concern, you DO have to look at the focal length spec; the zoom factor alone won't tell you that. Such info IS typically on the spec sheet, but maybe not on the marketing material, whereas zoom factor is usually a large-font, bold-face number plastered on the ad copy.
But what is the underlying thing that yields the dynamic range number? Nothing I know of.
None whatsoever. I used zoom power merely to illustrate a spec that doesn't give you all the information you may need.
Moreover, if you were to buy camera A only knowing that it had 10x more zoom, even if you were disappointed in the actual focal length, it would still have 10x more zoom, right?
Yes, but if that longer zoom range doesn't include the FOV that you need, that extra zoom doesn't really matter, does it? If you need an 80-degree or better FOV, a 10X 3-30mm is going to do the job while a 20X 6-120mm isn't.
U
Undisclosed #2
Apr 01, 2015Simply:
20x always means more focal range than 10x.
120dB sometimes means more dynamic range than 100dB.
AA
Ahmed Aziz
Apr 01, 2015For the sake of arguing if A says they are 120dB and B says the are 128x, can you state on paper only which one is better?
MI
Matt Ion
Apr 01, 2015Mathematically speaking, you should be able to directly correlate 'dB' and 'x' as both are just ratios. As noted in my post above, 3dB = 2x, and so on up the scale.
AA
Ahmed Aziz
Apr 01, 2015If the relationship you are stating is true, lets say 128x is 21 dB, even if WDR can not be really measured or it cant indicate the true performance of WDR in a camera. You cant really state that 21 dB is a good measure for a camera.
If you are looking for a PTZ camera with 120dB can this be acheived?
U
Undisclosed #2
Apr 01, 2015For digital imaging, dynamic range is typically referred to using 20 log, not 10 log, so 6db=2x, not 3db. Though apparently this is dangerous to just assume:
In connection with video and digital image sensors, decibels generally represent ratios of video voltages or digitized light levels, using 20 log of the ratio...
However, as mentioned above, the 10 log intensity convention prevails more generally in physical optics, including fiber optics, so the terminology can become murky between the conventions of digital photographic technology and physics. Most commonly, quantities called "dynamic range" or "signal-to-noise" (of the camera) would be specified in 20 log dBs, but in related contexts (e.g. attenuation, gain, intensifier SNR, or rejection ratio) the term should be interpreted cautiously, as confusion of the two units can result in very large misunderstandings of the value.
Could some manufacturers be using a different log for db's? Hard to say but looking at the Super Dynamic Range III Panasonic spec sheet (linked above by A ) and comparing the db with their fluff page x's metric yields this:
128x = 52 dB (NTSC), 160x = 54 dB typical (PAL)
In this case ironically, since they list both the x and the db we can tell that they are most likely using 6db=2x, not 3db=2x.
In any event, does the 120db Hikvision really have > 1000x the dynamic range of the 52db Panasonic or is there some fundemental disconnect between the methods used to derive the number. I say the latter...
MI
Matt Ion
Apr 01, 2015For digital imaging, dynamic range is typically referred to using 20 log, not 10 log, so 6db=2x, not 3db.
I kinda wondered about that, as 128x = 21dB seemed awfully low. Still, even at 20 log, 128x only = 42dB, so... not very good, at least if you're simply comparing spec sheets, not even up to the listing for the Samsung "WDR PTZ" I linked elsewhere.
Could some manufacturers be using a different log for db's? Hard to say but looking at the Super Dynamic Range III Panasonic spec sheet (linked above by A ) and comparing the db with their fluff page x's metric yields this:
128x = 52 dB (NTSC), 160x = 54 dB typical (PAL)In this case ironically, since they list both the x and the db we can tell that they are most likely using 6db=2x, not 3db=2x.
This would lead me to question what they're using for a starting point, since by my math (admittedly a bit rusty) a factor of 128 at 20log should be 42dB. Unless I missed a step...
6dB = 2x, 12dB = 4x, 18dB = 8x, 24dB = 16x, 30dB = 32x, 36dB = 64x, 42dB = 128x, 48dB = 256x, 54dB = 512x... and of course, 20dB = 10x and 40dB = 100x.
Granted most of my learning in this was back in my audio engineering days, working with dBV, dBm, dB SPL, etc., but logarithmetic (is that a word?) shouldn't be any different just because we're dealing with video.
But of course, as we've seen, there's no standardized method for measuring this, let alone anything that's enforced within the industry, so it's probably just as likely some marketers are simply pulling these numbers out of their butts.
U
Undisclosed #2
Apr 01, 2015This would lead me to question what they're using for a starting point, since by my math (admittedly a bit rusty) a factor of 128 at 20log should be 42dB. Unless I missed a step...
No, I think your math is right. The problem is that Panasonic's x factor is also a ratio! It's the ratio between the SDIII camera and a 'conventional camera'. Substitute whatever camera your convention requires... ;)
So, IMHO, the x thing is really even less useful than the dB, since it's a further derivation with an additional unknown. I only used it to glean from their NTSC to PAL spec that 2db difference was the difference (in their scale) from 128x to 160x, which (assuming that the dB values have unseen fractional precision), works out to 6db=2x.
MI
Matt Ion
Apr 02, 2015UI
Undisclosed Integrator #3
Apr 01, 2015Ahmed,
I am curious to know: what is the purpose of finding any correlations between both, if any ??? Just for mere personal intelectual curiosity or are you having an actual real project challenge ??
"Measuring how well a camera handles dynamic ranges in a scene is difficult, and the units typically used on product datasheets (such as dB) are NOT a reliable indication of actual WDR performance." to quote what "X" famous manufacturer is explaining in one of its whitepapers.
AA
Ahmed Aziz
Apr 01, 2015The question is for a real situation. I am having project for a critical infrastructure where the customer is only intrested in 120dB WDR. That is easy for the fixed cameras but when you are using a PTZ camera the datasheet measures the WDR in 'x'. Some other system integrators have a datasheet in dB but not in my case. So i thought I should try and get a clearer picture about this issue.
JH
John Honovich
Apr 01, 2015Ahmed,
You should educate your customers about the limitations and risks in depending on manufacturer stated dB ratings.
MI
Matt Ion
Apr 01, 2015As John has already mentioned, this measurement is not a difference in PTZs vs. fixed cameras, but merely a terminology THIS manufacturer has chosen to use. For example, this Samsung PTZ lists WDR range as 52-54dB, whereas this Vivotek claims WDR but doesn't appear to list the WDR range at all.
BG
Bob Germain
Apr 01, 2015Ahmed- where are you located? Hikvision has the DarkFighter PTZ with 120dB WDR in both Std and Integrated IR versions. Contact me at bob.germain@hikvision.com for further details and local contacts.
Bob
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