Digital or Optical zoom for Security Cameras

Digital or Optical zoom for Security Cameras

When shopping for security dome cameras with zoom capabilities, the question I ask myself is which is more important; digital or optical zoom?  When speaking of surveillance cameras you want to get “close” to a subject from a fixed camera position. The zoom control on your digital camera will let you get “close” enough to capture that bigger image. It will also let you zoom out to include a wide angle of view. 

What is optical zoom?

Optical zoom is a true zoom lens, which is physically extend to magnify your subject. A motor controls the lens movement. 

What is digital zoom?

Digital zoom is simply some in-camera image processing, basically decreasing the apparent angle of view of a digital photographic or video image. To make the cropped area bigger, digital zoom makes up, or interpolates, pixels to add to the image, which may give less than satisfactory results.

Zoom meaning the ability to make something distant appear closer. Basically it’s a ratio of the longest and shortest focal length.
A 17mm (Wide) to 50mm (Tele) lens would be roughly 3x zoom. (50/17 = 2.94)
However a 70mm (Wide) - 200mm (Tele) lens would also be a roughly 3x zoom. (200/70 = 2.86) 

Summary:
1. Optical zoom uses lenses to zoom in on the image before the sensor captures it.
2. Digital zoom uses the processor to magnify the image after the sensor captures it.
3. Optical zoom preserves the crispness and detail of the image while digital zoom tends to interpolate a lot of the data.
4. Cameras with optical zoom are generally more expensive and bigger than cameras that only have digital zoom.
5. Constant adjusting of the zoom level in a camera with optical zoom might drain the battery a little bit faster.

360 degrees of protection with the dome security camera

360 degrees of protection with the dome security camera

Pan/Tilt/Zoom cameras or PTZ cameras or 360degree cameras remain critical parts of many surveillance systems, especially in large security operations. Because of this it is important to understand and consider the key elements in selecting and using PTZ cameras.

In this guide we cover the basics of PTZ cameras and their selection, including:

• Pan/tilt/zoom basic terms
• Zoom ratios explained
• Using angle of view instead of zoom rating
• E-flip examined
• Available PTZ resolutions and their advantages/disadvantages
• Form factor selection (speeddomes, mini PTZs, positioners)
• Integrated IR PTZs
• PTZ lens issues
• Actual versus effective PPF
• Presets and tours
• Common applications

Pan/Tilt/Zoom Camera Basics

PTZs combine a camera with a motorized mechanism which allows it to move in multiple directions. These movements are referred to as:

• Pan: Left/right horizontal movement
• Tilt: Up/down vertical movement
• Zoom: Near and far 

This example demonstrates each of these movements:

Note that the extent to which cameras may be moved varies. Some models may be limited to 340° panning, some may tilt above horizontal, and zoom levels may vary from only slight magnification to extremely long distance. These specs depend on the type of PTZ (detailed below) and individual manufacturer/model.

E-Flip

Many PTZs include a feature called "E-flip" which automatically rotates the camera 180° when the operator is following a subject directly beneath it. This is a more intuitive control method than models which do not include E-flip, as the user must manually rotate the camera to follow the subject as they pass below.

This example shows the camera flipping as it is tilted down to 0° and beyond, while only the down tilt control is pressed.

Zoom Ratio

Manufacturers most often advertise PTZs using their optical zoom ratio, e.g., 18x, 26x, 36x, etc. This ratio is formed simply by dividing the camera's maximum focal length by its minimum, such as:

Use View Angle Instead

However, using only zoom ratio as an indicator of PTZ zoom performance misses some key details. Since lenses have differing wide/telephoto focal lengths, two cameras with the same ratio may have very different fields of view.

For example, looking at the specs of two 18x zoom cameras, we can see that one has a telephoto angle of view ~30% narrower (and thus higher PPF) than the other due to varying lens specs. But the reverse is also true, with the camera on the right having a wider possible angle of view, which may be more useful in some applications.

Users must beware of these issues when selecting PTZs and choose based on their required areas of interest. 

Ignore Digital Zoom

Some PTZ models include digital zoom in addition to optical, even in some cases  multiplying the two to create a deceptive "total zoom" figure, such as this camera:

However, digital zoom is a "fake" zoom, not providing additional details, only enlarging pixels captured and these specs should effectively be ignored in favor of angle of view as discussed above.

Resolutions Available

PTZs are now available in varying HD resolutions, as well as standard definition. Historically, zoom lenses for megapixel cameras were not available, though in the past few years, 1080p PTZs with 36x zoom have become readily available.

Note that HD is not necessarily preferable in PTZ applications, due to flaws in long focal length megapixel lenses, detailed later in this report.

PTZ Form Factors

There are three typical types of PTZ camera in use today, with different strengths and weaknesses, overviewed in this chart and detailed below:

Speeddome

The most common type of PTZ in use is the speeddome, which packages the camera/lens and pan/tilt mechanism in a dome form factor, typically 8-10" in diameter.

Speeddomes have several advantages:

• Pre-packaged: Due to their construction, speeddomes typically require less work to mount than positioning systems (below), and may be mounted in a variety of locations. Wall, pendant, recessed ceiling, and other mounts are all readily available.
• Integrated IR available: Several manufacturers now offer speeddomes with integrated IR (detailed further below), which greatly improves their usefulness in low light, as speeddomes historically have used relatively high F-Stop lenses, poor in dark scenes.
• Fast PTZ speeds: Speeddomes are the fastest movable cameras available. Speeds over 300º per second are not uncommon, and over 400º per second is not unheard of. This allows tracking of faster-moving subjects, and shorter movement times when switching between presets, often a fraction of a second.
• Pan/tilt range: Speeddomes typically feature full 360º pan range, without stops, and 180º tilt range with e-flip, to allow trailing of subjects as they move beneath the camera. Many cameras have extended tilt beyond 90º, with some offering up to 15º of up-tilt, above the horizon. Up-tilt previously required a pan/tilt positioner.
• Less wind loading: Compared to pan/tilt positioning systems, reviewed below, speeddomes do not have as many issues in strong winds, which may cause vibration in pan/tilt cameras.

Mini PTZ

Mini PTZ domes are a relatively recent development, with several manufacturers now offering models. These smaller PTZs have two key advantages:

• Low cost: Mini PTZs are must less expensive than full size speeddomes, often ~$300 USD or less, compared to $800-2000 for a speeddome.
• Small size: These models are much smaller than typical speeddomes, close to the size of a typical fixed dome camera (5-6" diameter) and much smaller in height.

However, there are disadvantages to mini PTZs as well:

• Limited zoom: Mini PTZs are typically limited to low optical zoom ratios such as 3x, though some may be found up to ~10x. Compared to other PTZs, often 30x or more, this is very low.
• Limited positioning range: Mini PTZs typically do not include full 360° panning, nor e-flip found in speeddomes.
• Slow pan/tilt speed: Panning speed of a mini PTZ is typically very low, 30-90 degrees per second, a fraction of speeddome panning speed.

Pan/Tilt Positioners

Pan/tilt positioners are the oldest type of movable camera system, available prior to integrated PTZ speeddomes. These systems historically consisted of separate componentes which were manually integrated: the positioner itself, a separate camera, and zoom lens. 

However, some manufacturers now offer pre-packaged IP positioning systems, such as the Axis Q86/Q87 and Pelco Esprit.

The key advantage to pan/tilt positioners is flexibility. Users may choose from multiple cameras and zoom lenses, instead of being limited to available speeddome options. This is useful when extremely long-range zoom lenses are required, as lenses over 100x zoom are available.

Positioners were previously the only option when infrared illuminators were desired in a PTZ camera. However, speeddomes with integrated IR have now largely caught up, offering long range infrared.

There are two key drawbacks to positioners:

• PTZ speed: Positioners often have low pan/tilt speeds, due to the weight and balance of cameras mounted on them. Increasing speeds could lead to increased vibration and "bounce" as cameras started and stopped moving, making tracking more difficult.
• Wind loading: Due to their increased profile, positioning systems in exposed areas may suffer from vibration due to wind, which is reduced or not present when using speeddomes.

Integrated IR Speeddomes

One recent advance in PTZ speeddomes is the addition of integrated IR, previously mainly found in positioners only. Many manufacturers now offer integrated IR speeddomes, such as Bosch, Dahua, Hikvision, and Samsung.

Integrated IR speeddomes have outperformed non-IR models in our tests at all ranges, with illumination at 450' and beyond. For example, the comparison below shows a 1080p IR PTZ versus a non-IR model at ~485' distance, with the subject clearly displayed in the IR model. The non-IR PTZ displays only noise, no usable image.

PTZ Lens Issues

When planning PTZ camera use, users should be aware that PTZ and other long focal length lenses do not resolve images the same as shorter focal length lenses, resulting in a reduction in practical details delivered. Because of this, when calculating needed PPF using PTZ cameras, users should expect a ~50% or higher reduction in delivered details.

For example, the image below shows a subject at ~420' using a 1080p camera, in an 87 PPF scene. However, details delivered are similar to ~35-40 PPF, less than half of actual.

Note that SD PTZs do not suffer typically suffer from these effects. For example, the VGA PTZ below displays a better image than the 1080p model at the same range, despite its much lower actual PPF.

PTZ Presets and Tours

In order to make PTZ operation easier, these cameras include the option to define predetermined positions, called "presets", which may be used to quickly move the camera to a specific position. For example, the clip below shows several presets covering a parking lot, quickly called in succession using a VMS.

In addition to presets, PTZs include tours (also called patterns) which move the camera automatically on a preset time schedule (typically every 3-10 seconds). Tours in current cameras most often call presets in a specific order (called a preset tour).

However, in the past, tours were typically defined by recording an operator manually moving the camera. This style of tour has generally fallen out of favor, though, as it becomes more difficult to spot small objects in motion as the camera is moving, and the constant PTZ movement precludes the use of camera-side video motion detection, which may be used in preset tours.

Most Common PTZ Applications

For the most part, PTZ usage is dropping in favor of fixed megapixel cameras, but there are still applications in which they are frequently used.

• Live monitoring operations: In systems with surveillance operators, PTZs are still often used, as they allow the user to more closely inspect and follow subjects than is possible with fixed cameras. Live monitoring is most often used in larger, higher security systerms, such as airports, critical infrastructure, city surveillance, etc., though many large retailers also employ PTZs and operators.
• Large areas: In very large areas, PTZs on preset patterns are still sometimes used instead of fixed megapixel cameras due to the higher details they may deliver at long range. For example, the image below compares 4K and 5MP cameras against HD and SD PTZs, with even the lowest resolution PTZ delivering details of the subject at this range:

What is IP camera ?

Network IP Cameras have been around for at over a decade now. Only recently have cabling installers began to pay attention to the technology because surveillance cameras have traditionally run on separate coaxial cable. Around 10 years ago, the first digital IP camera connected directly to a data network which changed the future of the surveillance camera industry.

During the early stages, the technology was not as professional as analog cameras. Most cameras were seen as ‘web cameras’, which were used to view objects or events over the internet or a LAN.

Today IP network cameras meet the same requirements and specifications as analog counterparts and in many areas surpass analog camera performance and features . Forecasts show that the network IP camera market share is growing at a much faster rate than its analog competitor and has surpassed the analog camera in market share.

An IP Camera is a networked digital video camera that transmits data over a Fast Ethernet link. IP Cameras (also called “network cameras”) are most often used for IP surveillance, a digitized and networked version of closed-circuit television (CCTV).

Benefits of IP camera over analog technology include:

• Remote administration from any location.
• Digital zoom.
• The ability to easily send images and video anywhere with an Internet connection.
• Progressive scanning, which enables better quality images extracted from the video, especially for moving targets.
• Adjustable frame rates and resolution to meet specific needs.
• Two-way communication.
• The ability to send alerts if suspicious activity is detected.
• Lower cabling requirements.
• Support for intelligent video.

Disadvantages of IP surveillance include greater complexity and bandwidth demands. One alternative for organizations with substantial investment in analog technology is to use a video server to, in effect, turn analog CCTV cameras to IP cameras. A video server is a small standalone server that converts analog signals to a digital format and provides the analog cameras with IP addresses.

Nevertheless, because it offers much more sophisticated capabilities, IP surveillance is increasingly replacing analog CCTV. An industry report from International Data Corporation (IDC) predicts that shipments of IP cameras and related products will increase 75% between 2012 and 2015.

Optical vs Digital Zoom

After reading the title of this article, you might be asking yourself, “Zooming is just zooming, right?”  Is there really a difference between optical and digital zooming?  You may be surprised to learn that yes, there is definitely a difference.

Optical zoom is considered as true zooming.  In other words, the lens optics on the camera itself are used to zoom in on an object.  This is opposed to digital zooming, in which the camera processes an image internally and focuses on a certain portion of that image.  That certain portion is simply enlarged, thus creating a zoom effect.

One such term is zoom.  Pan-tilt-zoom (PTZ) cameras and some fixed cameras have lenses that zoom in on an object.  In other words, it magnifies the object of the video, such as a car in a parking lot, so that it can be seen in much better detail.

Zoom is a very important feature of video camera lenses.  By making the image larger, it is possible to watch intrusions developing from some distance away from the doors to a building.

In a secure parking lot, for example, if someone bypasses the guard shack, a zoom camera mounted on the side of a building over a hundred feet away should be able to capture easily the progression of the automobile as it gets closer to the building.  This gives time for a security guard to respond before the intruder is leaning over his shoulder with a gun pointed to his head.

This may seem to be an extreme example, but it is one of the things that separates zoom cameras from fixed ones.

When comparing the zoom features of a camera lens, it is absolutely critical to understand the difference between digital zoom and optical zoom.

Digital Zoom

Imagine that you are looking at a Rembrandt in a museum, and you want to get closer to a beautiful pastoral scene to see the master’s details of a country hillside.

Since the guard is paying attention, you have to settle for taking a regular picture of the Rembrandt from a safe distance away.  Then, you have the picture developed and you now hold in your hand the photo you took at the museum.

You have an idea.  Now that you have the picture in hand, you decide to get someone to blow up the picture on a copier so that you can see the hillside better.  At least, that’s what you think you’re going to get.

When you blow the picture up to the same size of the full original painting, you are disappointed.  Now, it just looks like a bad case of psoriasis and you have missed an opportunity to bring Rembrandt home with you.

Digital zoom is very similar to this.  It cuts out a section on a distant image, not actually getting you closer to the object but by magnifying the lack of clarity that already exists.  In other words, if you can’t tell what the details are from a distance, you won’t be able to tell what they are by making it seem closer by digitally manipulating the captured picture.

Digital zoom, while not exactly useless, does not actually help very much when you need to focus on an object as if you are standing much closer to it.

Optical Zoom

Put yourself back in the art museum for a moment.  You are standing in front of the Rembrandt and you really want to get closer to it so you can see the finer details of the hillside.  This time, you don’t have a camera.  Instead, the sleepy-faced guard has his head turned, and you jump over the barriers and put your eyes about six inches away from the painting.

Suddenly, all the details of the hillside are shown.  You see the individual blades of grass, the lines on the outer edges which distinguish an object from its background.  You can see it clearly, and your awe of Rembrandt grows to new heights.

Optical zoom is like standing closer to the object.

In our opening example about the car crashing the guard shack, it would be as if the security guard is only a few feet away from the automobile, allowing him to head off the intruder before he reaches the front door.

The value of optical zoom in video surveillance is priceless.  While it is not quite as good as you will see on television cop shows, it is still a great tool for keeping an eye on your property.