Understanding IP Camera Specifications, What’s Important

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spec-illustrationIP Camera manufacturers provide product specification sheets that help you select the right camera for your IP security and surveillance system. But, which specifications are important?  They include such things as resolution, minimum light sensitivity, lens, WDR, signal to noise, etc.  This article reviews the important camera specs, and how to avoid being fooled by specsmanship (from the marketing department).

 

The importance of each of the camera specifications depends on your objective and application for your IP camera system.  For example, if you want to use the camera outdoors where it can get dark, then the low light specification is important. If you are only using the IP camera indoors, you may be more interested in the how wide a viewing angle you can achieve.  Here is a review of the important specifications.

Resolution

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This is an important specification.  In the old days it was measured in TV lines, and they used a TV test pattern to analyze the resolution.  Today resolution is usually defined by the total number of pixels in the sensor or the horizontal and vertical pixels.  Marketing people also use the term “HD” and “720p” or “1080p”, and most recently “4K”.  It can be very confusing.  Here’s what each of the terms mean:

 

Megapixel Camera:  This is a general term used for any camera that has over 1 million pixels in the sensor. There are many cameras that have over 1 megapixel resolution.  For example, there are 2.0, 3.0, 5, 8, 10 and higher megapixel cameras. The pixels are organized in a matrix of horizontal and vertical pixels.  The relationship between the horizontal and vertical pixels is called the aspect ratio.   The aspect ratio (vertical to horizontal ratio) is usually 4:3 or 9:16 (wide).  For example a 1.2 Megapixel sensor on the Sony SNC-EM600 camera has 1280 horizontal pixels and 1024 vertical pixels.  The aspect ratio is 1280/1024 which is 1.24 or close to the 4/3 ratio (1.3).  The 2 megapixel Samsung SND-6084 dome camera has 1920 x 1080 pixels, and the aspect ratio is closer to 16:9.  The latest sensors (especially the ones that claim 4K resolution) have different aspect ratios that are similar to the very wide formats used in the cinema market.

HD Camera:  This is more of a marketing term and is defined as either a 720p or 1080p type HD camera.  This specification comes from the video broadcast market rather than the security market and can be totally confusing.  Back in the old days, TV had only 525 horizontal scan lines per frame.  This is not the actual resolution, but rather physical scans of an electron beam on a CRT (Cathode Ray Tube). The total number of horizontal lines in a frame was made up of two fields (262.5 lines per field). The fields were interlaced, so we wouldn’t see the flicker.

Today 720p refers to 720 horizontal lines. The “p” indicates that the lines are progressive rather than interlaced.  There is only one scan per frame that includes 720 lines rather than 525 lines. The 1080p HD camera has at least 1080 horizontal lines.

720p cameras usually have a sensor with at least 1.0 megapixels. Pixel resolution is 1280 x 1024 (like the Sony SNC-EM600 1.3 megapixel camera), or it can be 1280 x 800 (like the Axis M3004 1.0 megapixel camera).

1080p cameras have at least a 2 megapixel sensor, and it is considered to be the higher resolution “HD camera”.  To confuse us, some manufacturers call their 3 megapixel or 5 megapixel camera “1080P” as well.

4K Camera:  This usually refers to a camera with over 8 Megapixels of resolution.  It has approximately 4,000 horizontal pixels. There is some difference between the definitions from the television industry and the security market.  The number of vertical and horizontal pixels and the aspect ratio are defined differently. For example Sony announced that their new (coming soon) camera has a chip with 4096 H × 2160 V pixels which runs at up to 60 fps and conforms to the Digital Cinema Initiative. Axis announced a camera with 3840 x 2160 which runs at up to 30 fps (which is called Ultra HD).  The marketing people call all these cameras “4K”.

 

Other Things that Affect Resolution:

The resolution of a camera is defined not only by the sensor, but also the lens and the electronic circuits. We sometimes see megapixel IP cameras selling for under $200.  Be careful.  You do get what you pay for.  The sensor may have the megapixels, but the lens may be plastic, and the result is a very low quality image. For more about IP Camera Resolution take a look at our blog article.

 

Minimum Illumination (or Low Light Sensitivity)

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The minimum illumination is the lowest light level that provides a reasonable image from the IP camera. It is measured in lux.  This can be very subjective.  It depends on what you think is an acceptable image.  The low light level image you see is not only dark, but can also be very noisy.

At the low light level the amplifiers are working very hard and there can be circuit noise that affects the video image.  This is called the signal to noise (S/N) ratio.  The better manufacturers also include the relative level of the signal (IRE), which is a measure of how hard the amplifier has to work.  For example a camera that is operating at 30 IRE is receiving 30 percent of the signal from the sensor circuits, while one operating at 50 IRE is receiving 50 % of the signal.  The lower the number, the harder the amplifier has to work to boost the signal so it can be seen.  The noise level can be as high as 20% of the signal so the resulting video can look very noisy when the signal level is very low.

The minimum light level is also affected by the shutter speed, which relates to the frame rate.  The longer the shutter is opened the more light can reach the sensor. The longer the shutter stays open, the lower the frame rate. There are some camera specs that indicate very low minimum illumination (0.0001 lux), but this is measured at a shutter speed of 0.5 sec.  This translates to a maximum frame rate of 2 fps.

The minimum illumination level is also determined by the lens.  The lower the f-number of the lens the more light it will let through.  For more details about this take a look at IP Camera Low Light Sensitivity blog article.

For a more practical guide to how IP cameras perform at low light, take a look at our “IP Camera Low Light Test” which compared a number of IP cameras at low light levels.

 

Lens:

lens-cbcMany IP cameras comes with a lens.  The lens allows you to frame the area that you want to see.  For example, a wide angle lens could be used to view a small room, while a narrow angle lens (with more magnification) can be used to see an area that’s far away.  The lens also can affect some of the other specifications such as minimum illumination, frame rate, and resolution.  If the IP camera doesn’t include a lens, it usually includes a standard type CS (or C) mounting capability, so you can use various third party lenses.

Lens angle:  The lens is measured in mm (millimeter).  The lower the number the wider the viewing angle. A 2 mm lens may have an angle of about 110 degrees, while a 50 mm lens has an angle of about 5.5 degrees.   The angle of the lens depends on the size of the sensor and the distance from the sensor to the lens.  Many manufacturers make it easy and provide both the mm and the angle of the lens in the specification. The right lens angle depends on your application.

Lens light capability:  The f-number of the lens indicates how well the light is transferred through the lens.  A camera with an f-number of f1.2 can pass more light than one that has f2.0 lens.  The f-number will also appear as part of the minimum illumination spec.  The lens angle can affect the f-number, the wider the angle the more light can get in, so the illumination spec is usually measured at the widest lens angle (when a variable lens is included).

Types of Lenses: There are fixed lenses, variable, and zoom lenses.

Fixed lens, as the name implies, has only one mm or angle setting.

Variable lens, can be manually adjusted through a range of angles.

Zoom lens is similar to the variable lens, but it can be controlled remotely. This allows you to adjust the setting of the camera lens from your computer making it very easy to install.

Iris:  Iris control adjusts how much light falls on the sensor.  There are manual iris controls, DC auto iris, and p-iris lenses.  The iris affects the depth of field.  The smaller the iris opening the longer the depth of field. When the scene is very dark the lens iris opens and the field of view is reduced.  This means some areas that are close or far away are not in focus.

Manual iris, is manually adjusted and depends on how much light is expected in the scene. A manual iris lens is usually used with indoor cameras where there is a small light variation.

DC auto Iris lens are usually used with outdoor cameras.  The camera electronics adjusts the iris opening depending on how much light it detects. At night it opens the iris and when there is bright sunlight it closes the iris.

P-Iris lenses are similar to the DC auto iris lens, except they add additional intelligence to the lens opening.  When the iris is closed all the way, it can reduce the clarity of the image (when used with megapixel cameras).  It has to do with the pixel size.  A p-iris camera system works with the camera electronics to prevent the iris from closing all the way.  On the other hand, when the view is very dark, the camera tries to open the iris to let in as much light as possible.  As the iris increases the depth of field is reduced.  A p-iris lens prevents the lens from opening all the way and compensates by increasing the camera amplification of the video signal.

Focus:  The focus of the IP camera can be adjusted either by adjusting the lens or by remotely adjusting the distance between the lens and the sensor (back focus).  Lenses can have a fixed focus (that can’t be changed) or manual focus.  “Back focus” is not part of the lens, but is usually listed with the lens specification.  This is a very nice feature that makes installation much easier.  The focus can be adjusted at the computer, instead of at the camera.  Many of the new Sony and Samsung cameras have this feature.

IR Corrected Lenses:  Lenses bend the light to achieve the right focus and magnification.  IR light can bend at a different angle than visible light when the wrong type of glass is used in the lens.  IR corrected lens compensates for the focal difference and provides a much clearer image.  This is most apparent at higher resolution.  If you plan to use a megapixel IP camera system, then make sure you get the IR type lens.

 

Special Applications that Require Specific Capability

Wide Dynamic Range

When you are trying to view an area with challenging lighting conditions it’s best to select a camera that provides good wide dynamic range (WDR).  For example, when you view a lobby with a large window, you will need a camera that either provides back light control or better yet WDR.  Wide dynamic range has been dramatically improved in the latest cameras.   WDR is measured in dB.  The older cameras provided about 50 dB of WDR, and the new Sony and Samsung cameras provide over 120 dB.  In many cases you don’t have to pay more for this capability, you just have to select the right camera.

Frame Rate

I moved this specification to this section because these days frame rates are not critical in most applications.  Most megapixel cameras support reasonably good frame rates.  What is reasonable?  Well, it depends on the application.  In the old days people said you needed at least 30 fps.  That, of course is not true in most applications.

The video is very smooth even at 10 fps.  Take a look at our video “How the Video camera Works” for more details about frame rates and how they have evolved from the old days of TV.  Yes, there are a few applications where you want higher frame rate, such as in gambling casinos, or in special testing situations, where you need to see very fast motion, but in most cases you can save bandwidth and storage by reducing the frame rate.

In certain cases the frame rate has to be reduced.  For example, frame rates tend to be lower in very high resolution cameras (over 3 Megapixel).  The Arecont 10 Megapixel cameras support frame rates up to 7 fps, which isn’t too bad for most applications.  The frame rate can also be affected by very low light situations. By increasing the time that the shutter stays opened, you can improve the low light performance of most cameras. But, be careful.  If you increase the shutter speed to 0.5 seconds, the maximum frame rate is only 2 fps.

Audio

Audio capability can be very important in some applications.  For example, if you would like to connect anintercom to the camera you will need two-way audio. You also will require audio in applications like police interrogation rooms.  In this case you need a camera with audio input capability.  You can also select a camera with a built in microphone, but be careful because it’s always best to have the microphone close to the person talking.

Input and Output (I/O)   

If you plan to release a door lock, you need an output signal to control a relay that can open an electric lock.  If you want to detect that a door has been opened and start recording video, then you will require an IO input connection to the camera.

 

Summary

Understanding the specifications, allows you to select the right camera for your IP camera system.  Before reviewing the specifications, make sure you know your application and objectives.  Sometimes the specs are confusing, so always check with us if you have questions. Camera specifications such as resolution, low light sensitivity and the lens are some of the important factors to consider when selecting your camera.

If you need help understanding the IP camera specifications and selecting the right camera, don’t hesitate to give us a call or send a message.  We have a lot of experience with IP security systems, so I’m sure we can be helpful.  We can be reached at 1-800-431-1658 (in the USA), or 914-944-3425, or use our contact form.