Xinsheng IntelligentWritingsIndustrial Camera 50 Questions (2)

11: What is the meaning of pixel depth in industrial cameras?

The digital signal output by the digital camera, that is, the gray value of the pixel, has a special number of bits, which is called the pixel depth. The orientation of this value is usually 8-16bit for black and white cameras. The pixel depth defines the number of gray levels from dark to light. For example, for an 8bit camera 0 means full dark and 255 means full light. A number between 0 and 25 represents a certain brightness index. 10bit data has 1024 gray levels and 12bit has 4096 gray levels. For each application we have to carefully consider whether very fine grayscales are required. Rising from 8bit to 10bit or 12bit can indeed enhance the measurement accuracy, but it also reduces the speed of the system and increases the difficulty of system integration (the cables increase, the size becomes larger), so we must choose carefully.

12: What interfaces do industrial cameras have?

The interface refers to the interface between the camera and the lens. Commonly used lens interfaces are C, CS, and F.

13: How are industrial cameras classified?

1. According to the chip structure classification: CCD camera & CMOS camera

2. According to the sensor structure: area scan camera & line scan camera

3. According to the output mode classification: analog camera & digital camera

4. Color Camera & Monochrome Camera

14: What is the difference between industrial cameras and ordinary digital cameras?

1. The shutter time of industrial cameras is very short, which can clearly capture fast-moving objects, while ordinary cameras capture fast-moving objects very blurred;

2. The image sensor of an industrial camera is scanned progressively, while the image sensor of an ordinary camera is scanned interlaced, or even scanned every three lines;

3. The shooting speed of industrial cameras is much higher than that of ordinary cameras; industrial cameras can take ten to hundreds of pictures per second, while ordinary cameras can only take 2-3 pictures;

4. The output of industrial cameras is raw data, and its spectral range is often relatively wide, which is more suitable for high-quality image processing algorithms, and is widely used in machine vision systems. And the pictures taken by ordinary cameras, its spectral range is only suitable for human vision, and after MPEG compression, the image quality is also poor;

15: How to choose a line scan camera?

1. Calculation resolution: Divide the width by the minimum detection accuracy to obtain the pixels required for each line.

2. Detection accuracy: The actual detection accuracy is obtained by dividing the width by the pixels.

3. Number of scanning lines: The number of scanning lines per second is obtained by dividing the length of the movement speed per second by the precision.

An example of selecting a line scan camera based on the above calculation results is as follows:

For example, the width is 1600mm, the precision is 1mm, and the motion speed is 22000mm/s. Camera: 1600/1=1600 pixels, at least 2000 pixels, selected as 2k camera, 1600/2048=0.8, and actual accuracy of 22000mm/0.8mm=27.5KHz should be selected The camera is a 2048 pixel 28kHz camera

16: What are the characteristics of line scan cameras?

1. Line scan sensors used in line scan cameras usually have only one row of photosensitive units (a few color line scan sensors use three rows of photosensitive units)

2. The line scan camera only captures one line of images at a time;

3. The line scan camera only outputs one line of images at a time;

4. Compared with traditional area scan cameras, area scan captures several lines of images each time and outputs them in frames.

17: Why use line scan cameras in machine vision inspection?

1. Line scan cameras have higher resolution; line scan cameras are generally 1024, 2048, 4096, 8012 pixels per row; while general area scan cameras are only 640, 768, 1280, and area scans larger than 2048 are rare .

2. The acquisition speed of line scan cameras is faster; the acquisition speed of different types of line scan cameras ranges from 5,000 lines per second to 60,000 lines per second. Users can choose a few lines or every dozen lines to form a frame of image for processing once. So high frame rates can be achieved.

3. The line scan camera can continuously collect and process without interruption; the line scan camera can continuously collect objects that move in a straight line (linear guides, paper, fabric, printed matter, objects on conveyor belts, etc.).

4. The line scan camera has a simpler and more reasonable structure. Compared with area scan cameras, line scan cameras do not waste resolution to capture useless data.

18: What is a smart industrial camera?

An intelligent industrial camera is not a simple camera, but a highly integrated miniature machine vision system. It integrates image acquisition, processing and communication functions into a single camera, thus providing a multi-functional, modular, high-reliability, and easy-to-implement machine vision solution. An intelligent industrial camera is generally composed of an image acquisition unit, an image processing unit, an image processing software, and a network communication device. Due to the application of the latest DSP, FPGA and large-capacity storage technologies, its intelligence has been continuously improved, which can meet the application requirements of various machine vision.

19: What are the main parameters of CCD chip and CMOS chip?

The two main types of photoelectric sensor chips used in machine vision are CCD chips and CMOS chips. abbreviation. Whether it is CCD or CMOS, their function is to convert optical signals into electrical signals (voltage/current) through the photoelectric effect, and store them to obtain images. The main parameters of CCD chip and CMOS chip are:

1. Pixel size

Pixel size refers to the actual physical size of each pixel on the chip pixel array. The usual sizes include 14um, 10um, 9um, 7um, 6.45um, 3.75um, etc. The size of the pixel reflects the responsiveness of the chip to light to some extent. The larger the size of the pixel, the more photons it can receive, and the greater the number of charges generated under the same lighting conditions and exposure time. For low-light imaging, pixel size is an indication of chip sensitivity.

2. Sensitivity

Sensitivity is one of the important parameters of the chip, and it has two physical meanings. One refers to the photoelectric conversion capability of an optical device, which has the same meaning as the responsivity. That is, the sensitivity of the chip refers to the output signal voltage (current) per unit of exposure within a certain spectral range, and the unit can be nanoamps/lux, nA/Lux, volts/watt (V/W), and volts/lux (V/Lux) , Volts/lumen (V/lm). The other refers to the ground radiation power (or illuminance) that the device can sense, which has the same meaning as the detection rate. Units can be expressed in watts (W) or lux (Lux).

3. Bad Pixels

Due to the limitations of the manufacturing process, for a sensor with several million pixels, it is almost impossible for all pixels to be good. The number of dead pixels refers to the dead pixels in the chip (pixels that cannot be effectively imaged or corresponding The number of pixels whose inconsistency is greater than the allowable range of the parameter), and the number of replacement points is an important parameter to measure the quality of the chip.

4. Spectral response

Spectral response refers to the ability of the chip to respond to light of different wavelengths, which is usually given by the spectral response curve.

20: What is the difference between a line scan camera and an area scan camera?

Line scan CCD industrial cameras are mainly used in image processing in the fields of industry, medical, scientific research and security. In the field of machine vision, line scan industrial cameras are a special kind of vision machine. Compared with area scan industrial cameras, its sensor has only one line of photosensitive elements, thus enabling high scanning frequency and high resolution. A typical field of application for line scan industrial cameras is the inspection of continuous materials such as metals, plastics, paper and fibers. The object to be detected usually moves at a uniform speed, and one or more industrial cameras are used to continuously scan it line by line to achieve uniform detection of its entire surface. The image can be processed line by line, or the area image composed of multiple lines can be processed. In addition, line scan industrial cameras are very suitable for measurement occasions, thanks to the high resolution of the sensor, it can measure accurately down to the micron.

For the area array CCD, it has a wide range of applications, such as the measurement of area, shape, size, position, and even temperature. The advantage of the area array CCD is that it can obtain two-dimensional image information, and the measurement image is intuitive. The disadvantage is that the total number of pixels is large, and the number of pixels per line is generally less than that of the linear array, and the frame rate is limited, while the advantage of the linear array CCD is that the number of one-dimensional pixels can be done a lot, and the total number of pixels is relatively small. Area array CCD industrial cameras are few in number, and the pixel size is relatively flexible, and the number of frames is high, which is especially suitable for the measurement of one-dimensional dynamic targets.