Industrial cameras are the core components of machine vision systems, widely used in various fields such as industrial production, urban surveying, and grain sorting, especially for quality control, production monitoring, and measurement tasks. Compared with conventional cameras, industrial cameras have the characteristics of being sturdy and durable, and can cope with adverse environmental conditions such as high temperature, high humidity, and dust.
Industrial cameras have different classification forms, which can be divided into CCD cameras and CMOS cameras according to chip types; According to the structural characteristics of sensors, they can be divided into linear array cameras and area array cameras; According to the scanning method, it can be divided into interlaced scanning cameras and progressive scanning cameras; According to the resolution size, it can be divided into regular resolution cameras and high-resolution cameras; According to the output image signal format, it can be divided into analog cameras and digital cameras; According to the output color, it can be divided into black and white cameras and color cameras. Next, Beijing Yingmeizhi editor will briefly introduce the difference between black and white cameras and color cameras.
Black and white cameras and color cameras are easy to understand literally. The images output by black and white cameras are black and white, which are grayscale signal values without color information; The images output by color cameras are colored, and color cameras are divided into true color cameras and pseudo color cameras.
Both CCD and CMOS image sensors convert photons into electrons, where the number of photons is proportional to the number of electrons. For each pixel, counting its number of electrons forms a grayscale image that reflects the intensity of light. In other words, CCD and CMOS image sensors are "color blind" and do not have the ability to distinguish colors, only forming black and white images.
monochrome camera
When light shines on the photosensitive chip, the photon signal will be converted into an electronic signal. As the number of photons is proportional to the number of electrons, counting the number of electrons can form a black and white image that reflects the strength of light. After being processed by the microprocessor inside the camera, the output is a digital image. In black and white cameras, the color information of light is not preserved. As shown in Figure 1, left: black and white mode.
True color camera
CCD and CMOS image sensors cannot distinguish colors and can only sense the strength of the signal. In this case, in order to capture color images, a prism can be used to divide the light into optical primary colors (RGB), and then three photosensitive chips can be used to sense the intensity separately, and then combined together. As shown in Figure 1: Triprism mode.
True color cameras capture images with good quality and no loss of details, but such cameras have complex structures and require specialized lenses, which are generally expensive.
Pseudo color camera
Considering price factors, Kodak's Bayer proposed an inexpensive compromise solution (pseudo color camera): using only one image sensor to solve color recognition. His approach is to set up a filter in front of the image sensor, which is covered with filter points and corresponds one-to-one with the pixels in the lower layer. As shown in Figure 3 (right), the arrangement of filter points on the Bayer filter is regular: 2 red dots, 2 blue dots, and 4 green dots are distributed around each green dot. Due to the human eye being the most sensitive to green, green is twice as red and blue. Due to the fact that each filter point can only pass through one color among red, green, and blue, all pixels should have information about these three colors when outputting. The two filtered color component values are compensated for through interpolation in the later algorithm processing. As shown on the right of Figure 1: Bayer filter mode.
summary
The significant advantage of pseudocolor cameras is that they can save costs, and the vast majority of color cameras on the current market use this technology. However, black and white cameras capture photons of all wavelengths, while pseudocolor cameras only accept photons from the three RGB bands and perform a de mosaic neighborhood averaging operation, resulting in weaker luminous flux and detail performance compared to black and white cameras.
Comparing the imaging performance of color cameras and black and white cameras in the same environment, we can draw the following conclusion: in industrial applications, if we want to process images related to color, then we need to use color cameras; If not, it is best to choose a black and white camera because at the same resolution, the accuracy of a black and white camera is higher than that of a color camera.
