Camera Selection – How Can I Find the Right Camera for My Image Processing System?

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 casings 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.

• 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.
• are typically used in a variety 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.

• 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.
• 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.

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.

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.

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

• strong value for the performance
• high frame 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 frame rates without deterioration in image quality.

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.

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.

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)

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

Resolution = Height/(Eye detail) = (2,000 mm)/(1 mm) = 2,000 px in x and y = 4 MP

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

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.

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.

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.

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.