The "Not-so-Obvious" things to take note for cameras

[ryeporta 0]

Hi all .. I intend for this topic to go beyond the usual specs like:

• TVL / Pixels
  Min Lux
  Lens (3.6mm/6.0mm/etc)
  etc

 

 

Obviously this section not too useful for the "whats-the-cheapest-cam" group of buyers .. but might be(I think) critical for those who require for important/specialised installations .. some questions may be weird though ..

 

FEEL FREE to add on any additional things that u've come across that falls into this category so that future readers can benefit from a one-stop place to learn all the "hidden details" for camera selection.

 

Interlaced vs Progressive Scan

• 
  * Are ALL analog cameras using interlaced scan by default?
  * Are DVR (Analog) Progressive or Interlaced?
  * For network cams .. If it is not specified, will it be safe to assume it uses interlaced scanning?
  

 

Lag in IP Cam

• 
  * What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)
  * Is there anyway to tell from spec sheet if there will b a lag?
  

 

Signal/noise Ratio

• What is a "good" S/N ratio?
  Is S/N ratio critical for IP Cams? I browsed thru few of my brochures but there is no S/R ratio ratings on them?

 

Size of sensor

I understand that size of sensor affects the image quality of the video. It seemed like the specs of most of the reputable brands have the following trend:

- Below 1MP : 1/4"

- 1 to 2MP: 1/3"

- 2 to 3MP: 1/3" or smaller

 

[list=]So can I expect quite a big dip in the image quality for example a 2MP on 1/4" CMOS? Assuming both uses progressive scan

[survtech 0]

Hi all .. I intend for this topic to go beyond the usual specs like:

• TVL / Pixels
  Min Lux
  Lens (3.6mm/6.0mm/etc)
  etc

 

 

Obviously this section not too useful for the "whats-the-cheapest-cam" group of buyers .. but might be(I think) critical for those who require for important/specialised installations .. some questions may be weird though ..

 

FEEL FREE to add on any additional things that u've come across that falls into this category so that future readers can benefit from a one-stop place to learn all the "hidden details" for camera selection.

 

Interlaced vs Progressive Scan

• 
  * Are ALL analog cameras using interlaced scan by default?
  * Are DVR (Analog) Progressive or Interlaced?
  * For network cams .. If it is not specified, will it be safe to assume it uses interlaced scanning?
  

 

Lag in IP Cam

• 
  * What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)
  * Is there anyway to tell from spec sheet if there will b a lag?
  

 

Signal/noise Ratio

• What is a "good" S/N ratio?
  Is S/N ratio critical for IP Cams? I browsed thru few of my brochures but there is no S/R ratio ratings on them?

 

Size of sensor

I understand that size of sensor affects the image quality of the video. It seemed like the specs of most of the reputable brands have the following trend:

- Below 1MP : 1/4"

- 1 to 2MP: 1/3"

- 2 to 3MP: 1/3" or smaller

 

[list=]So can I expect quite a big dip in the image quality for example a 2MP on 1/4" CMOS? Assuming both uses progressive scan

Your answers, in order, are:

* Yes, CCTV analog cameras are all interlaced. Machnine Vision and a few special applications excepted.

* Pretty much all DVRs record in Progressive (non-interlaced) mode.

* Most network cameras are progressive scan.

* Lag (latency) is caused by a number of factors: the largest being the encoding (compression) and decoding (decompression) processes, with smaller amounts caused by the network.

* I don't recall many, if any, cameras listing latency. It also depends on the codec used and settings within the codec.

* 50db is considered "good" S/N

[ryeporta 0]

Your answers, in order, are:

* Yes, CCTV analog cameras are all interlaced. Machnine Vision and a few special applications excepted.

* Pretty much all DVRs record in Progressive (non-interlaced) mode.

* Most network cameras are progressive scan.

* Lag (latency) is caused by a number of factors: the largest being the encoding (compression) and decoding (decompression) processes, with smaller amounts caused by the network.

* I don't recall many, if any, cameras listing latency. It also depends on the codec used and settings within the codec.

* 50db is considered "good" S/N

 

Thanks SurvTech

[Soundy 1]

Interlaced vs Progressive Scan

• 
  * Are ALL analog cameras using interlaced scan by default?
  * Are DVR (Analog) Progressive or Interlaced?
  * For network cams .. If it is not specified, will it be safe to assume it uses interlaced scanning?
  

NTSC and PAL specify interlaced video, so yes, pretty much all analog cameras will use this as well, for compatibility. I have seen a few that had the option to switch to progressive (the Pelco IS90 comes immediately to mind).

 

Network cameras are not beholden to analog specs, so they don't need to use interlaced video... as such, very few will, if any (I've never seen one that specifically stated it was using interlaced scanning).

 

Lag in IP Cam

• 
  * What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)
  * Is there anyway to tell from spec sheet if there will b a lag?
  

I've never seen it listed... it really wouldn't be something easily quantified, since as survtech notes, it's dependent on so many different factors, most of them outside the camera itself (network latency, decoding efficiency of the VMS, etc.), and many of them dependent on specific user settings.

[lukater1974 0]

* For network cams .. If it is not specified, will it be safe to assume it uses interlaced scanning?

Actually one of the advantages of IP cams is they have a progressive scan sensor

 

Lag in IP Cam

• 
  * What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)
  This happens especially with cheap cams using (pseudo)H.264 codek in facts this codek in some cases requires a lot of processing power from PC side (read Pentium 4 or 5 processor)
  * Is there anyway to tell from spec sheet if there will b a lag?
  

High quality IP cams don't have this problem since the producer was able to create a lighter codek or a camera that can do the biggest part of the job requiring less work from computer side

 

Size of sensor

I understand that size of sensor affects the image quality of the video. It seemed like the specs of most of the reputable brands have the following trend:

- Below 1MP : 1/4"

- 1 to 2MP: 1/3"

- 2 to 3MP: 1/3" or smaller

 

Actually most of the "reputable brands" use 1/2 C-MOS (or 1/3 ccd)sensor since C-mos sensor (vs ccd) has problems with working under low light conditions so a bigger size of the sensor means a brighter image

[ryeporta 0]

Thanks everyone for your generous sharing

 

So .. I gather that for my question:

"What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)"

 

The likely cause is the will be the codec issue? So it has nothing to do with the processor in the camera itself?

 

New Question 01:

I've got a entry level IP Cam from Vivotek n it lags like 1/2sec! The higher end models that my supplier showed me runs really smooth. I am just curious why the same manufacturer will want to develop diff codec for different range of camera?

 

New Question 02:

Have anyone tried those cheap IP Cams from network products companies like Linksys / D-Link / etc?

What do you feel about those?

[Soundy 1]

Thanks everyone for your generous sharing

 

So .. I gather that for my question:

"What is the cause of the lag in IP Cam? (Actual motion vs actually seeing it on screen)"

 

The likely cause is the will be the codec issue? So it has nothing to do with the processor in the camera itself?

It has a lot to do with the processor. "Codec" stands for "compression/decompression" and simply refers to the method/format/algorithm used to compress the data for transmission, then decompress it for display. That compression is done by whatever processor (DSP, CPU, etc.) is used in the camera. If it's a low-power or poorly-designed processor, then compression will take longer. If it's a poorly-designed or poorly-implemented codec, the compression will take longer (think of an instruction procedure that's 100 pages vs. 2 pages, for example - both might get you to the same point, but one will take a lot longer to complete).

 

New Question 01:

I've got a entry level IP Cam from Vivotek n it lags like 1/2sec! The higher end models that my supplier showed me runs really smooth. I am just curious why the same manufacturer will want to develop diff codec for different range of camera?

Two things: first (and most obvious), the higher-end camera will use a more powerful processor, and thus be able to compress the video faster; second, they may not necessarily be using the same codec - one camera may use MJPEG and the other H.264, for example.

 

Related to that second issue, and as noted above, some codecs are not well-designed, or the version a manufacturer uses may not be well-implemented. An example might be (not saying this is the case with your cameras) that the manufacturer licenses (at a cost) a better, more efficient, more streamlined H.264 codec for their higher-end camera, but uses a less-efficient but FREE open-source version for the cheap camera (combine that with a weaker processor, and yeah, you've got lag).

 

Sometimes the problem can be on the receiving end as well. H.264, for example, doesn't really take a lot of work to compress at the camera end. On the viewing end, however, a crappy codec can take a lot more of the computer's CPU to decode. Classic example was when I was bench-testing two H.264 cameras, one a Panasonic, one a Pelco: watching the 3MP Pelco's display on my older Pentium M laptop was painful in the extreme - slow, clunky, poor refresh, actually caused the laptop's Windows desktop to freeze now and then... the 5MP Panasonic played back cleanly with no stuttering.

[Soundy 1]

BTW, don't get too hung up on "lag time" (aka latency). Except in a very few specific circumstances, it really won't affect anything. Consider that most of the time you'll be more concerned with recorded video, which is "lagged" by design, by hours, days, weeks, even months.

[ryeporta 0]

BTW, don't get too hung up on "lag time" (aka latency). Except in a very few specific circumstances, it really won't affect anything. Consider that most of the time you'll be more concerned with recorded video, which is "lagged" by design, by hours, days, weeks, even months.

 

Thanks for the sharing Soundy