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Wednesday, August 12, 2009

Resolution and Pixels and Frame Rates OH MY!!!

There is a lot of confusion about all the different image sizes, frame rates, resolution etc. To be honest it has been very confusing to me. So I went on a small quest to discover the real answers. Much of what I found was on some tech forums where they were discussing the in's and out's of video. Also key points come from John Honovich as well with

Differences between capture, display and storage resolution.

Resolution can be very confusing because there are several different applications of it. In this article you will find our best attempt to explain the differences in as much of a non-technical manner as possible.

First to identify a few terms to help guide us. With the advent of high definition TV a new term has developed referring to the old TV format has standard definition. That terminology has seemed to creep into video security as well. A camera could be referred to has standard definition which basically means it is not a megapixel camera. However a camera may be called a High Resolution camera but it is still a standard definition camera. Now an analog camera or IP camera for that matter could be 380 TV lines of resolution and it would be called a low res camera. However, a camera with 540 TV lines would be called a high res camera. However they could both be considered standard definition cameras because they are not megapixel cameras or HDTV cameras. We will explain more about megapixel and IP in a moment.

In CCTV Video Security Systems the main differences of resolution are capture, display and storage resolution.

Capture or Camera resolutions for analog cameras

When reading a security camera specification sheet, you will see two sets of numbers rating the sensor of the camera. One lists the number of pixels (768 H X 494 V) for the sensor and the other rates the horizontal resolution (TVL) of the camera.

Effective pixels = 768 (Horizontal) X 494 (Vertical)
Horizontal resolution = 540 TV lines

The difference between the two is pixel aspect ratio and picture aspect ratio. The pixel aspect ratio has to do with the actual number of pixels that sensor is able to capture. The picture aspect ratio is based on what the NTSC standard for analog signals (composite video) has been designed to process. The numbers are different but using the math behind it you can calculate how the two relate. We will avoid the math for this discussion.

Since analog standard definition security cameras do not have square pixels there are two types of picture aspect ratio. There is storage aspect ratio and display aspect ratio.

Storage Aspect Ratio

The storage aspect ratio is the digital size of the image as it is stored on digital media. For instance the highest stored resolution using composite video (which is what comes from an analog camera) is 720x480. That is the same as a standard definition DVD movie.

When storing video on an analog security DVR you have several resolution options. The typical Settings available for storage are CIF, 2CIF and 4CIF.

CIF352 x 240
2CIF704 x 240
4CIF704 x 480

Display Aspect Ratio

The display aspect ratio can only be displayed as what is referred to as a 4:3 aspect ratio which is the NTSC standard. This limits the number of lines of data that can actually be displayed. This explains why a 768 horizontal sensor when displayed on a 4:3 aspect monitor will result in only 540 TV lines of resolution. (note: a standard definition movie on a dvd could be in 4:3 or 16:9 format but the pixel size would still be 720x480 for storage purposes.)

Newer standards for TV have introduced High Definition TV with an aspect ration of 16:9 which allows for a greater number of lines of resolution to be displayed. Newer technology of cameras are now able to capture higher resolutions which will now allow for storing and displaying these higher resolutions.

Standard Resolution IP Cameras

Standard resolution IP cameras can produce the same resolutions options as shown above for DVR storage and the video data can be stored on a HDD using any PC that the camera software is installed on. They can usually also do full D1 resolution which is 720 x 480. Standard resolution IP Cameras can also capture 30fps. Typically they are setup to run at lower resolutions and frame rates to help with bandwidth and storage of the data.

Megapixel resolution IP Cameras

Just a note about megapixel IP cameras. Megapixel cameras can capture video at much higher resolutions but are not necessarily the same as High Definition as in HDTV. HDTV has a very specific set of resolutions available. 720p HDTV is 1280 x 720 and 1080p HDTV is 1920 x 1080. HDTV also operates at 30fps.

A megapixel camera that is 1.3 megapixels has a resolution of 1280 x 1024. From there the megapixels go up. 2, 3, 5, and on up to 16mp. However they are not able to capture images at 30 fps. They typically are only capturing 3 to 7 fps. Megapixel cameras can display higher than HDTV resolutions on PC monitors that support higher resolutions.

Take a look at the chart below to see how some of the more common resolutions compare.

Other Resolutions Compared

Designation H x V
CIF -------- 352 x 240
2CIF ------- 704 x 240
4CIF ------- 704 x 480
D1 --------- 720 x 480
720p HDTV -------- 1280 x 720
1.3MP ------ 1280 x 1024
2MP -------- 1600 x 1200
1080p HDTV ------- 1920 x 1080
3MP --------- 2048 x 1536
5MP --------- 2592 x 1944
11MP --------- 4000 x 2656
16MP --------- 4872 x 3248

Well I hope that clears things up at least a little bit. If you have any further qustions feel free to post a comment or two!!

By Peter Brissette
Sales Manager
GSP America

Click here to learn more about Megapixel security cameras


Dr Bob said...

Good post - it's always good to hear how a messy topic can be cleaned up and explained clearly once you gather all the facts together. Thanks for putting all the numbers in one place.
Dr Bob (Bosch)

San Diego Roofing said...

Typically they are setup to run at lower resolutions and frame rates to help with bandwidth and storage of the data.

Unknown said...

Yes you are correct about using lower settings to help with storage and bandwidth.

That is one of the biggest challenges for using higher resolution and megapixel cameras. You must take those factors into consideration in order to make sure your system is going to give you what your expecting.

wrought iron gates texas said...

It is a informative and helpful tips as many of us don't know what the product or even hesitate to discuss but here we have learned that thing's are not hard enough now and we can learn it and make a good selection while going for any kind of CCTV or Camera when we want to install it and what are the various option we have.