Effectiv Pixels vs TV Lines

[gster 0]

Hi everyone

 

Can anyone properly explain to me how effective pixels relates to TV Lines and if TV Lines can be calculated using effective pixels?

 

Every camera manufacturer seems to prefer a slightly different method of stating resolution such as:

 

Resolution: 410K (i.e. 410,000 pixels?)

Effective (or Active) Pixels: 752 x 582 (i.e. 437,664 pixels?)

 

Are all these figures basically different ways of stating the same thing or do they actually mean different things?

 

Thanking you all in advance

 

Cheers

 

Gster

[Jasper 0]

That is the same thing I was trying to figure out in the beginning. You need to look at the specs for each camera to get an idea. Alot of them will have an estimate of the horz x vertical.

 

TVL

This is a measure of the resolution of a video device. Higher number is higher resolution. 380 TVL is considered medium resolution. 480 TVL or greater is considered high resolution.

 

What resolution would you like to capture at?

[rory 0]

See if you can read anything out of this article

http://www.dpreview.com/learn/?/Glossary/Camera_System/Effective_Pixels_01.htm

 

I know though alot of Bullet cameras claim 480TVL, the active pixels are less than that found in a Box camera with 480TVL from a brand such as GE. You can notice it when you put them side by side, it makes a huge difference. If you want to see them let me know, Ill post them here, same store, 2 different cameras claiming 480TVL. Ill have to wait until daylight now though.

 

Once again, you get what you pay for

 

Effective Pixels

By Vincent Bockaert

 

Effective Number of Pixels

 

A distinction should be made between the number of pixels in a digital image and the number of sensor pixel measurements that were used to produce that image. In conventional sensors, each pixel has one photodiode which corresponds with one pixel in the image. A conventional sensor in for instance a 5 megapixel camera which outputs 2,560 x 1,920 images has an equal number of "effective" pixels, 4.9 million to be precise. Additional pixels surrounding the effective area are used for demosaicing the edge pixels, to determine "what black is", etc. Sometimes not even all sensor pixels are used. A classical example was Sony's DSC-F505V which effectively used only 2.6 megapixel (1,856 x 1,392) out of the 3.34 megapixel available on the sensor. This was because Sony fitted the then new 3.34 sensor into the body of the previous model. As the sensor was slightly larger, the lens was not able to cover the whole sensor.

 

 

So the total number of pixels on the sensor is larger than the effective number of pixels used to create the output image. Often this higher number is preferred to specify the resolution of the camera for marketing purposes.

 

Interpolated Number of Sensor Pixels

 

Normally, each pixel in the image is based on the measurement in one pixel location. For instance, a 5 megapixel image is based on 5 million pixel measurements, give and take the use of some pixels surrounding the effective area. Sometimes a camera with, for instance, a 3 megapixel sensor, is able to create 6 megapixel images. Here, the camera calculates, or interpolates, 6 million pixels of information based on the measurement of 3 million effective pixels on sensor. When shooting in JPEG mode, this in-camera enlargement is of better quality than those performed on your computer because it is done before JPEG compression is applied. Enlarging JPEG images on your computer also makes the undesirable JPEG compression artifacts more visible. However, the quality difference is marginal and you are basically dealing with a slower 3 megapixel camera which fills up your memory cards twice as fast—not a good trade-off. It is similar to what happens when you use a digital zoom. Interpolation cannot create detail you did not capture.

 

Fujifilm's Super CCD Sensors

 

Normally sensor pixels are square. Fujifilm's Super CCD sensors have octagonal pixels, as shown in this diagram. Therefore, the distance "d2" between the centers of two octagonal pixels is smaller than the distance "d1" between two conventional square pixels, resulting in larger (better) pixels.

 

 

However, the information has to be converted to a digital image with square pixels. From the diagram you can see that, for a 4 x 4 area of 16 square pixels, only 8 octagonal pixel measurements were used: 2 red pixels, 2 blue pixels, and 4 green pixels (1 full, 4 half, and 4 quarter green pixels). In other words, 6 megapixel Super CCD images are based on the measurement by only 3 million effective pixels, similar to the above interpolated example, but with the advantage of larger pixels. In practice the resulting image quality is equivalent to about 4 megapixel. The drawback is that you have to deal with double the file size (leading to more storage and slower processing), while enjoying a quality improvement equivalent to only 33% more pixels.

[Jasper 0]

That's why I like your advice because I can spend weeks researching and because of your experience with so many products you know what is good.

 

If I was to buy that 420TVL bullet CVC-325WPSW you recommended would that compare to some of the cheaper 480TVL cameras you have seen?

 

If I was to go up to 520TVL BW would that be overkill if recording at 640x480 on a Geovison using MPEG-4?

 

If a 480TVL or 520TVL camera would make a difference in overall quality do you know of any bullet cameras with IR that you could recommend or is the CVC-325WPSW good enough?

 

Thanks

[Jasper 0]

Wrong place to post that question. Also realized that bullet camera is 380TVL not 420. Anyway, oops.

[rory 0]

Thanks man

 

Okay, Quality between a 480 and 420 will depend on the brand name and products you are looking at. 420TVL BW can look alot crisper sometimes than 480 TVL Color as it is in monochrome only and does not need to produce color, basically.

 

Some will argue that all cameras are Color from the start, and then a BW camera basically cuts out the chromo which then produces a monochrome image.

 

Also, not all 420TVL BW cameras will give the same quality image, for example Provideo has a cheaper BW 420TVL Bullet, but ive used it and it sucks compared to the CVC-325 BW Bullet camera's quality.

 

BW cameras go as high as 600TVL.

 

No thats not overkill, heck Im viewing and recording 480TVL cameras in 720x480 mode and it makes a huge difference from even 640x480 mode.

 

If you want color 480 is the highest you need for DVRs right now, though there are some such as Sanyo and Bosch that claim 520 and 540TVL with their cameras, basically it is digitized is all.

 

Only High res Day Night Bullet with an Auto IR Cut Filter that I could recommend is one posted by Spytown previously, the Provideo CVC-7706DNV. Ive never actually used it personally but seen it in action, and others on this forum have used it, Specs are impressive for a Bullet camera.

 

Ofcourse dont expect it to match up with an Extreme CCTV camera, but at what it cost it comes pretty close.

 

Price wise it may be out of your budget, it is EXpensive ... i like to use BW in low light, and color where there is light, myself, as I know I cant afford that camera

[rory 0]

the provideo one is 420TVL, this is it here, same exact model I use:

http://www.ezalarms.com/ezStore123/DTProductZoom.asp?productID=26802

 

Course then I could also point you to the WizKid BW High Res Bullet Camera, not much different in price but higher res and longer warranty

[rory 0]

Also. quality will depend on your DVR and Monitor used.

And an LCD will not provide as clear video as a CRT.

 

Also if you use the Geo DSP output it will be much better quality as it is basically analogue video, but you will need a TV or CCTV Monitor.

 

Rory

[Jasper 0]

I like that WizKid bullet specs of 560TVL, but doesn't have IR and don't want to spend money for an Illuminator. Well maybe a burglar will bring a powerful enough flashlight?

 

I saw those pictures in another thread of the 420TVL bullet camera and I am impressed with the image quality. You said the IR on those were basically useless so maybe I'll try the WizKid?

 

Have you ever used the High-Res WizKid bullet?

If the IR doesn't really work on the other camera than I might as well go for the WizKid or look for another camera that does have IR that will work

[rory 0]

no IR really works on Bullet cameras, except in small spaces like rooms, etc.

Even the provideo I listed wont do anything short of the following,

 

For any IR to work, it needs to reflect off something, Unless you use an IR that Floods the area (UF500).

 

Bullets can be annoying as people can move them.

 

Ill check out the Sanyo Day Night dome and give some feedback on it.

Otherwise the WZ30B5 high res BW Vandal Dome will work. But if you need a wall mount, then the WZ46 is designed for that.

 

They can always add IR if needed.

 

I would suggest motion lighting anyway for security, as well as a decent alarm system, maybe some yard beams.

[Jasper 0]

Yeah, I think the idea of putting in some flood lights with a motion sensor and a timer would be the solution.

 

Do you know if there is a way for me to use the Geovison software to maybe help me in this regard?

 

You must be an all-nighter like me. It will be daylight there pretty soon.

 

Thanks again.

[rory 0]

its just turning daylight now

 

what do you want Geo to do for yah?

 

They have data in and outs for that.

 

I personally use Optex for outdoor beams, etc, you could tie them

into the DVR easily.

 

Or just use Motion Sensor Lights, they are the cheapest solution, like $30. I have a couple clients that use it even in their retal store.

 

Rory

[Jasper 0]

I have not really looked into the full capablities of the Geovison software. The motion floodlights on a timer is the easiest solution the more I think about it.

 

I just need to put a timer for it to come on after hours when the bar is empty. I thought maybe their might be a way to activate the lights through using the Geovision software when the camera detects motion, but who wants to run cable unless they need to, if Geovision is even capable of that feature?

[rory 0]

Relying on DVR motion detection though ..

 

Take a look at the Optex products, they have wired and also wireless.

 

Basically anything you can think of, can be done without a problem, with Geo or Without it.. Ive not used Geo's full capabilities either, maybe scott J can shed some light on it, or someone else.

 

I think we are in the wrong thread though

[Jasper 0]

Sorry about that I keep forgetting, I guess I am tireder than I thought.

 

Thanks for all the information, much appreciated.

[scottj 0]

Jasper,

 

Add a standard alarm system motion sensor to activate the lights and begin recording on the Geo machine. If you rely on just the motion detection in a dark environment from the camera, you may miss out on something. Add a DI/DO board and use one of the contacts to the motion sensor. Very easy to do.

 

scottj

[Thomas 0]

Having played with a resolution testing chart and screwed up my tests.... I can pretty safely say that you could fudge the numbers with ease for resolution.

[Jasper 0]

Thanks I will look into how to hook that up. Very good detterent and lots of nice light for the cameras to say "Smile your on candid camera".

 

As far as resolution is concerned a picture truly is worth a thousand words. That picture I saw of Rory's BW 420TVL camera looked very clear. He has some nice comparison shots.

 

Sample photos like that are very helpful. Specs and reality are sometimes very different.

 

Thanks

[Cooperman 0]

Without wishing to state the obvious, the measure of a cameras resolution is a pretty academic exercise, unless you also take account of the lens fitted.

 

If you fit a rubbish lens on a high resolution camera, it may actually look worse than a medium resolution camera fitted with quality optics.

 

I think the main reason that good quality high res. bullets are so few and far between, is that the mass produced barrel lenses just aren't up to the job.

[Jasper 0]

No go ahead state the obvious. It is not so obvious for a lot of people in this forum, I for one at this point.

 

The people that know the information already can go, oh! I already knew that, the others will go, oh! I did not know that, that's good to know.

 

So, many others are appreciative about what is obvious to others in this forum are not so obvious to others. I wish I could just remember everything I have forgotten that I once knew. Sometimes it’s nice to be reminded of what seems so obvious.

 

Thanks

[scottj 0]

obviously.....

[videobruce 0]

I know this is a older thread, but:

 

Let me understand this correctly; This spec of 'resolution' with a CCTV camera is only based on the number of pixels on the chip, not the actual measured output resolution of the camera??