The answers usually provide a good initial guidance and will point in one of these two directions:

Network (IP) Cameras

IP-Cam

Industrial (MV) Cameras

IP-Cam

Decision #1: Network or Industrial Camera?

Cameras for image processing systems are categorized either as industrial/machine vision (MV) or network/IP (Internet Protocol) cameras.

Network cameras record videos. They are frequently used in classical surveillance applications and in combination with industrial cameras.
Some of their typical characteristics:

  • often placed within robust housings designed to be resistant to jolts and harsh weather, making them suited for use indoors or out.

  • a variety of functions such as day/night modes and special infrared filters deliver outstanding image quality even under extremely poor lighting and weather conditions.

  • they compress the images they record. This reduces the volume of data to such a degree that it can be stored in the camera. By connecting to a network, a theoretically unlimited number of users can also access the camera.

Industrial cameras, by contrast,

  • send the images as uncompressed (‚raw‘) data directly to the PC; The PC is then responsible for processing the relatively large volume of data. The benefit of this method is that no image information is lost.

  • Industrial cameras comprise two technologies: area and line scan cameras. They capture images differently, which is relevant to the type of vision application.

Excursion: How Area and Line Scan Cameras Capture Images

An image is composed of a specific number of lines.

Area scan cameras are outfitted with a rectangular sensor featuring numerous lines of pixels that are exposed at the same time. The image data is thus recorded in one single step, and is also processed in the same way.



applications for areascan cameras

Area scan cameras are typically used in a variey of industrial applications, in the medical and life sciences, in traffic and transportation, or in security and surveillance, often as a supplement to network cameras.

Line scan cameras by contrast use one sensor comprised of just 1, 2 or 3 lines of pixels. The image data is captured line for line, with the individual lines then reconstituted into an entire image during the processing stage. The question of whether an area or line scan camera should be used is a question of your applications and its requirements.

applications for linescan cameras

Line scan cameras are used universally when products must be inspected as they pass by on conveyor belts — at times at extremely fast speeds. Typical industries include printing, sorting and packaging, food and beverage, and all kinds of surface inspection applications.

applications for network cameras

Network cameras are used for a variety of surveillance tasks, from process controls in shipping lines and packing systems to building and traffic surveillance systems. They are typically used in places like banks, casinos, company campuses and public buildings, as well as in logistics and transportation centers such as harbors or freight centers.




Decision #2: Monochrome or Color Camera?

A relatively simple decision and one that is usually answered by what your application is all about: the image you require. Do you need it in color to evaluate the results, or is black and white sufficient? If color isn‘t mandatory, then a monochrome camera is typically the better choice as they are more sensitive and deliver more detailed images. For many applications, for example in intelligent traffic systems, a combination of b/w and color cameras are also frequently used to satisfy the specific national legal requirements for evidence-grade images.

Decision #3: Sensor Types, Shutter Techniques, Frame Rates

This step involves picking a suitable sensor, built either around CMOS or CCD sensor technology, and choosing the type of shutter technique: global or rolling shutter. The next consideration is of the frame rate, meaning the number of images that a camera must deliver per second to handle its task seamlessly.

Sensor Types

Excursion: CCD or CMOS?

The fundamental difference between the two sensor technologies is in their technical structure.

In CMOS chips, the electronics to convert the light (and specifically: the photons) into electronic signals (electrons) are integrated directly into the surface of the sensor. This makes them especially quick since they can read the image data more rapidly and allow the user to address the image range flexibly. CMOS sensors are heavily used in the consumer market, such as in SLR cameras.

CCD sensors use the entire sensor surface to capture the light, with no conversion electronics placed on the sensor‘s surface. This leaves more space for pixels on the surface, which in turn means more light is captured. Sensors of this type are thus extra light-sensitive, a major benefit in low-light applications like astronomy. CCD sensors deliver outstanding image quality in slower applications, although their architecture and the way in which they transport and process image data has increasingly brought them to the limits of their speed.

Over the years, the CMOS technology has progressed so far that it is now suitable for almost any image processing applications. CMOS sensors offer

  • strong value for the performance
  • high image rates
  • high resolution
  • low power consumption
  • strong quantum efficiency

which helped them gain a foothold in areas previously dominated by CCD sensors. One especially strong selling point of today’s generation of CMOS sensors is their high image rates without deterioration in image quality.

The trend on the sensor market is increasingly pointed toward CMOS technology, especially after Sony, one of the biggest CCD sensor manufacturers, announced the discontinuation of its CCD sensor production.

CMOS and CCD sensor
CMOS area scan sensor and CCD sensor

Shutter Techniques

One simple, but crucial requirement here: the shutter must match the application. The shutter protects the sensor within the camera against incoming light, opening only at the moment of exposure. The selected exposure time provides the right 'dose' of light and determines how long the shutter remains open. The difference between the global and the rolling shutter variants is in the way they handle exposure to light.

Excursion: How Global and Rolling Shutter Work

The global shutter opens to allow the light to strike the entire sensor surface all at once. Depending on the frame rate a moving object is thus exposed in a rapid succession. Global shutter is the optimal choice for applications where very fast moving objects must be captured, such as in the traffic and transportation fields, in logistics and in inspections of printed materials.

gobal shutter scheme global shutter example

The rolling shutter exposes the image line-by-line. Depending on the selected exposure time, distortions can occur when objects move during the exposure process - the so-called rolling shutter effect. However, there‘s no need to abandon the possibility of a rolling shutter just because your application involves moving objects. In many cases, the effect can be circumvented through proper configuration of the exposure times and the use of an external flash.


rolling shutter scheme
For the rolling shutter, the exposure time does not begin and end simultaneously, but rather for each individual row respectively:
The graphic shows the staggered exposure of the individual rows on the photo.

Learn more about these shutter techniques in our white paper„Global Shutter, Rolling Shutter — Functionality and Characteristics of Two Exposure Techniques“.

Frame Rate

Used synonymously with ‚frames per second‘ or ‚fps‘, or ‘line rate‘ or ‚line frequency‘, respectively, for line scan cameras. The frame rate describes the number of images that the sensor can capture and transmit per second.


application example for fast frame rate requirement
For fast-moving applications like inspections of printed images, with newspapers moving at high speeds past the camera inspection point, the cameras must be able to ‚shoot‘ in milliseconds.

The higher the frame rate, the quicker the sensor.
=> The quicker the sensor, the more images it captures per second.
=> The more images, the higher the data volumes.


application example for low framerate
This is a far cry from some microscopic inspections used in medicine and industry, which typically require only low frame rates.
areascan cameras offering different framerates
For area scan cameras these volumes can vary greatly depending on the interface and whether a low rate of 10 fps or a high (fast) speed of 340 fps is being used. Just which frame rates are possible or even necessary depends on what the cameras in the image processing system must record.

Decision #4:
Resolution, Sensor and Pixel Sizes

Resolution

There’s a strong relationship between these three factors (as explained earlier in this article).

Looking up your camera’s specs you read „2048x1088“. What exactly does that tell you? It describes the number of pixels per line, in this case 2048 pixels for the horizontal lines and 1088 pixels in the vertical lines. Multiplied together, the numbers indicate a resolution of 2,228,224 pixels, or 2.2 megapixels (million pixels, or ‚MP‘ for short).

To determine which resolution you require for your application, doing some simple maths will help instantly:


Resolution = (Object Size) / (Size of the detail to be inspected)

Excursion: How to Determine the Required Resolution

how to determne the required resolution

Let’ say you need to capture a precision image of the eye color of a roughly 2m tall person standing at a specific point:

resolution=height/eye detail = 2m/1mm = 2,000 pxl in x and y= 4mp

To clearly recognize the 1 mm large detail, you need a resolution of 4 megapixels.

Sensor and Pixel Size

Fact #1: The easy part first: large sensor and large pixel surfaces can capture more light. Light is the signal used by the sensor to generate and process the image data. So far, so simple. Now stay with us: The greater the available surface, the better the Signal-to-Noise Ratio (SNR), especially for large pixels measuring 3.5 µm or more. A higher SNR translates into better image quality. A SNR of 42 dB would be considered a solid result.

Fact #3: And yet large sensors and a large number of large pixels won‘t achieve much unless the right optics are in place. They can only achieve their full potential when combined with a suitable lens also capable of depicting such high levels of resolution.

Fact #2: A large sensor provides larger space onto which more pixels can fit, which produces a higher resolution. The real benefit here is that the individual pixels are still large enough to ensure a good SNR — unlike on smaller sensors, where there is less space available and thus smaller pixels must be used.

Fact #4: Large sensors are also always more cost intensive, since more space means more silicon.

Decision #5:
Interfaces and
Housing Size

Interface

Interface example

The interface serves as the liaison between the camera and PC, forwarding image data from the hardware (the camera sensor) to the software (the components that process the images). Finding the best interface for your application means finding the optimal balance of performance, costs and reliability by weighing a series of different factors against one another.

factors of interface decisions
Depending on what your application demands, you can select between Camera Link, GigE or USB 3.0 to find the best set of properties to transmit image data from the camera to the PC quickly and securely.

Excursion: Interface Technologies and Standards

GigE Vision, USB3 Vision and CameraLink cameras

GigE Vision, USB3 Vision and Camera Link are modern, widely available technology standards that guarantee the compatibility of the camera interface with standard-conformed components and accessories. Each technology is designed to fulfil a specific set of requirements regarding bandwidth, multi-camera setups, of cable lengths, for example.

FireWire and USB 2.0 are older technologies which, due to their limitations, are not recommended without reservation for modern image processing systems anymore.

Comparsion of different camera interfaces
Comparison of Interfaces

Not sure, which interface technology matches your requirements best?
Check our Interface Advisor for support in making your choice.

Want to explore all the pros and cons of the individual interfaces in detail?
Download our White Paper „Comparison of the Most Common Digital Interface Technologies in Industrial Machine Vision“.

Housing

Directly tied to the choice of interface is the size of the camera housing. It is important in terms of the overall integration into the vision system. In applications where cameras are organized next to one another (known as multi-camera setups) to better record the entire width of a material web, each millimeter of space matters.


Size matters, especially in multi-camera setups.
At Basler for example the portfolio of available models ranges from the 29 mm x 29 mm of the Basler ace to the larger dimensions of individual cameras with very large (line scan) sensors, such as the Basler sprint series.

Decision #6:
Useful Camera Features

All Basler cameras come equipped with a core of helpful features to improve image quality, assess image data more effectively or control processes with greater precision. Check our Features Check List for a comprehensive listing of all features for each camera model.

When designing your image processing system, you will most probably come across these three features:

AOI (Area of Interest)

Allows you to select specific individual areas of interest within the frame, or multiple different AOIs at once. The benefit here is that only those parts of the frame are processed that are of relevance for assessment of the image, thus speeding up the read out of the camera data.

Autofeatures

Basler cameras offer a series of so-called Autofeatures such as, for example, automatic exposure adjustment and automatic gain. By allowing the exposure time and gain parameters to adapt automatically to changing ambient conditions, these two Autofeatures keep the image brightness perpetually constant.

Sequencer

The sequencer is used to read out specific image sequences. This means for example that various AOIs can be programmed and then automatically read out sequentially by the sequencer.

See the Clearing Ahead?

Almost there! After making your way through the jungle of criteria and components, after venturing out into explorations along your path of necessary decisions, you’re just steps away now from the final challenge: the right camera!

Fear no more! Let the Basler Camera Selector help you choose precisely what you need: the perfect area scan, line scan or network camera for your individual requirements.

Check out our Area Scan Camera Selector

 
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