Xinsheng IntelligentWritings50 questions about industrial cameras (1)

1: What is the cause of the frame loss problem of industrial cameras?

There are often some machine vision engineers who think that industrial cameras with USB interfaces will cause frame loss. Generally speaking, the frame loss of industrial cameras has nothing to do with the transmission interface used by the industrial camera, whether it is USB, 1394, GigE, or CameraLink. Poorly designed drivers or industrial camera hardware is the real cause of frame loss: the reason why a poorly designed industrial camera loses frames is that the data channel is blocked and cannot be processed in time, so when a new image comes in, The previous image may be forced to be discarded, or the new image may be forced to be discarded. To solve this problem, designers need to make precise design for each link of driver and industrial camera hardware data transmission.

2: What are the input and output interfaces of industrial cameras?

In machine vision inspection technology, the input and output interfaces of industrial cameras include Camera Link, IEEE 1394, USB2.0, Ethernet, and USB3.0;

3: Knowing the length, width, height and required measurement accuracy of the object to be measured, how to choose a CCD camera and an industrial lens, and what should be paid attention to when choosing the above devices?

The first thing to do is to choose the right lens. The selection of lenses should follow the following principles:

1). What is the chip size of the matching camera;

2). What is the interface type of the camera, C interface, CS interface or other interface;

3). The working distance of the lens;

4). The angle of view of the lens;

5). Lens spectral characteristics;

6). Lens distortion rate;

7). The size of the mechanical structure of the lens;

When choosing a CCD camera, you should consider the following aspects:

1). Type of photosensitive chip; CCD or CMOS

2). Video features; including point frequency and line frequency.

3). Signal output interface;

4). The working mode of the camera: continuous, trigger, control, asynchronous reset, long time integration.

5). Video parameter adjustment and control method: Manual, RS232.

At the same time, when choosing a CCD, it should be noted that l inch = 16mm instead of 25.4mm.

4: What is the difference between a CCD camera and a CMOS camera?

1. Imaging process

The principle of photoelectric conversion between CCD and CMOS image sensor is the same. The main difference between them is that the readout process of the signal is different; because the CCD has only one (or a few) output nodes to read out uniformly, the consistency of its signal output is very good; In the CMOS chip, each pixel has its own signal amplifier, which performs charge-voltage conversion, and the consistency of its signal output is poor. However, in order to read out the entire image signal, the CCD requires a wide signal bandwidth of the output amplifier. In a CMOS chip, the bandwidth requirement of the amplifier in each pixel is low, which greatly reduces the power consumption of the chip. This is the CMOS chip. The main reason for lower power consumption than CCD. Despite the reduced power consumption, the inconsistency of the multi-million amplifiers results in higher stationary noise, again an inherent disadvantage of CMOS over CCD.

2. Integration

From the point of view of manufacturing process, the circuits and devices in CCD are integrated in semiconductor single crystal material manufacturers, and the process is relatively complicated. Only a few manufacturers in the world can produce CCD wafers, such as DALSA, SONY, Panasonic, etc. The CCD can only output analog electrical signals, which requires subsequent processing by address decoders, analog converters, and image signal processors. It also needs to provide three groups of power synchronous clock control circuits with different voltages, so the integration level is very low. CMOS is integrated on a single material called metal oxide. This process is the same as the process of producing tens of thousands of semiconductor integrated circuits such as computer chips and storage devices. Therefore, the cost of sound field CMOS is much lower than that of CCD. . At the same time, the CMOS chip can integrate the image signal amplifier, signal reading circuit, A/D conversion circuit, image signal processor and controller into one chip. Only one chip can realize all the basic functions of the camera, and the integration is very high. The high, chip-scale camera concept was born from this. With the continuous development of CMOS imaging technology, more and more companies can provide high-quality CMOS imaging chips, including: Micron, CMOSIS, Cypress, etc.

3. Speed

CCD adopts photosensitive output one by one, which can only be output according to the specified program, and the speed is relatively slow. CMOS has multiple charge-voltage converters and row-column switch control, and the readout speed is much faster. At present, most high-speed cameras above 500fps are CMOS cameras. In addition, the address strobe switch of CMOS can be randomly sampled to realize sub-window output, and higher speed can be obtained when only the sub-window image is output.

4. Noise

CCD technology has developed earlier and is relatively mature. It uses PN junction or silicon dioxide (SiO2) isolation layer to isolate noise, and the imaging quality has certain advantages over CMOS photoelectric sensors. Due to the high integration of CMOS image sensors, the distance between components and circuits is very close, the interference is serious, and the noise has a great impact on the image quality. In recent years, with the continuous development of CMOS circuit noise reduction technology, good conditions are provided for the production of high-density and high-quality CMOS image sensors.

5: What are the main parameters of industrial cameras?

1. Resolution

2. Speed (frame rate/line rate)

3. Noise

4. Signal to Noise Ratio

5. Dynamic range

6. Pixel depth

7. Spectral response

8. Optical interface

6: How is the resolution of an industrial camera defined?

Resolution is the most basic parameter of the camera, which is determined by the resolution of the chip used by the camera, and is the number of pixels arranged on the target surface of the chip. Usually the resolution of the area scan camera is represented by two numbers, horizontal and vertical resolution, such as: 1920 (H) x 1080 (V). Indicates the number of rows of cells, ie 1080 rows. Now the resolution of the camera usually indicates how many K, such as 1K (1024), 2K (2048), 3K (4096) and so on. When capturing images, the resolution of the camera has a large impact on the image quality. When imaging the same large field of view (scene range), the higher the resolution, the more obvious the display of details.

7: What does the frame rate and line rate of an industrial camera mean?

The frame rate/line rate of the camera indicates the frequency of the camera's acquisition of images. Usually, the area scan camera is indicated by the frame rate, in units of fps (Frame Per second), such as 30fps, which means that the camera can collect up to 30 frames of images in 1 second; The camera usually uses the line frequency as the unit of KHz. For example, 12KHz means that the camera can collect up to 12,000 lines of image data in 1 second. Speed is an important parameter of the camera, and in practical applications it is often necessary to image moving objects. The speed of the camera needs to meet certain requirements in order to image the object clearly and accurately. The frame rate and line frequency of the camera are first affected by the frame rate and line frequency of the chip, and the maximum design speed of the chip is mainly determined by the highest clock that the chip can withstand.

8: What does the noise of industrial cameras mean?

The noise of industrial cameras refers to the signals outside the actual imaging target that are not expected to be collected during the imaging process. According to the European camera test standard EMVA1288, the noise in the defined camera can be generally divided into two categories: one is the statistical fluctuation noise that conforms to the Poisson distribution brought by the effective signal, also called shot noise. ), this noise is the same for any camera, unavoidable, especially deterministic calculation formula. (That is: the square of the noise = the mean of the signal). The second category is the inherent signal-independent noise of the camera itself, which is caused by the image sensor readout circuit, camera signal processing and amplifying circuit, etc. The inherent noise of each camera is different. In addition, for digital cameras, quantization noise will be generated when the video signal is converted to analog, and the higher the quantization bits, the lower the noise.

9: What does the signal-to-noise ratio of an industrial camera mean?

The signal-to-noise ratio of a camera is defined as the ratio of signal to noise in the image (the ratio of the average gray value of the effective signal to the root mean square of the noise), which represents the quality of the image. The higher the signal-to-noise ratio of the image, the better the image quality.

10: What does dynamic range mean in industrial cameras?

The dynamic range of the camera indicates the range of the light signal detected by the camera. The dynamic range can be defined by two methods. One is the optical dynamic range, which refers to the ratio of the maximum light intensity at saturation to the light intensity equivalent to the noise output. It is determined by the characteristics of the chip. Decide. The other is electronic dynamic range, which refers to the ratio between saturation voltage and noise voltage. For a fixed camera, its dynamic range is a fixed value and does not change with changes in external conditions. In terms of linear response, the dynamic range of the camera is defined as the ratio of the saturated exposure to the noise equivalent exposure: dynamic range = full well capacity of the photosensitive element/equivalent noise signal dynamic range can be expressed in terms of multiples, dB or Bit. The larger the dynamic range, the more adaptable the camera is to different light intensities.