Industrial cameras are core components of machine vision systems, widely used in various fields, especially for production monitoring, measurement tasks, and quality control. Industrial digital cameras are typically more robust and durable than conventional standard digital cameras. This is because they must be able to withstand various complex and changing external influences, such as operating in harsh environments with high temperatures, high humidity, and dust. Industrial cameras can be classified in many ways; the following diagram shows some common classification methods.
Area scan camera and line scan camera
The difference between area scan cameras and line scan cameras lies in their image acquisition methods. Area scan cameras acquire images on a plane basis, directly obtaining complete two-dimensional image information, while line scan cameras acquire images on a line basis. Although these are also two-dimensional graphics, they are longer in length but only a few pixels wide. This is because the sensor of a line scan camera has only one row of photosensitive elements. Although area scan cameras have a larger total number of pixels, the number of pixel units distributed in each row is less than that of line scan cameras. Therefore, the resolution and scanning frequency of area scan cameras are generally lower than those of line scan cameras.
Because the photosensitive elements of a line scan camera are linear, the acquired image information is also linear. To acquire complete image information, scanning motion is often required. This is useful for acquiring images of materials such as metals and fibers moving at a constant speed in a straight line. Linear image sensors are primarily CCDs , although some linear CMOS image sensors have appeared on the market . However, linear CCDs remain the mainstream. Currently, the solution of acquiring images using a trapezoidal CCD combined with scanning motion is widely used, especially when a large field of view and high image resolution are required. Area scan cameras can be used for area, shape, and position measurement, or surface quality inspection. Directly acquiring two-dimensional graphics can reduce the complexity of image processing algorithms to some extent. In practical engineering applications, the choice must be based on the specific engineering requirements.
Black and white cameras and color cameras
Black and white cameras and color cameras are easy to understand: a black and white camera outputs a black and white image, while a color camera outputs a color image.
Let's first look at a simple monochrome camera. When light shines on the image sensor, photon signals are converted into electronic signals. Since the number of photons is proportional to the number of electrons, counting the number of electrons allows us to form a monochrome image that reflects the intensity of light. After processing by the camera's internal microprocessor, the output is a digital image. In a monochrome camera, the color information of light is not preserved.
In reality, CCDs cannot distinguish colors; they can only sense signal strength. In this case, to acquire color images, theoretically, a beam splitter could be used to separate the light into the three primary colors ( RGB ), then three CCDs could be used to sense the strength of each color separately, and finally the results could be combined. This approach is theoretically feasible, but using three CCDs and a beam splitter drastically increases the cost. The best approach is to use only a single CCD to output all color components.
CCD and CMOS
Image sensors are the core components of industrial cameras, and there are two main types: CCD and CMOS .
CMOS (Complementary Metal Oxide Semiconductor) is a semiconductor technology. Each pixel in a CMOS image sensor array consists of three parts: a photodiode, an amplifier, and a readout circuit. However, because each unit outputs independently, the output of each amplifier is not identical. Therefore, CMOS arrays tend to produce images with higher noise and relatively lower image quality, although they can still meet general accuracy requirements. In the field of integrated circuits, CMOS uses the most basic process technology, which is relatively simple and therefore inexpensive, offering advantages such as high photoelectric sensitivity. Its performance parameters are constantly being optimized, and its applications are becoming increasingly widespread. Overall, CMOS offers a relatively high cost-performance ratio.
CCD ( Charge-coupled Device ) is a semiconductor device that converts optical images into digital signals . Tiny photosensitive elements embedded in a CCD are called pixels; the more pixels a CCD contains, the higher its image resolution. CCDs offer excellent image quality, noise reduction, and flexibility in camera design. Although the addition of external circuitry increases system size and complexity, it also allows for greater flexibility in circuit design, maximizing performance in areas of particular interest to CCD cameras. CCDs are well-suited for applications with very high performance requirements but less stringent cost controls, such as astronomy, high-resolution medical X- ray imaging, and other scientific applications requiring long exposures and stringent image noise control.
Currently, CCD still outperforms CMOS in terms of performance . However, with the continuous advancement of CMOS image sensor technology, its inherent advantages of integration, low power consumption, and low cost have led to significant improvements in noise and sensitivity, narrowing the gap with CCD sensors .
