Detailed explanation of frame rate related knowledge of industrial camera parameters：

Industrial cameras are one of the important components of machine vision systems, and they play a very important role in machine vision systems. Industrial cameras have been widely used in industrial production line online inspection, intelligent transportation, machine vision, scientific research, military science, aerospace and many other fields.

The main parameters of industrial cameras include: resolution, frame rate, pixels, pixel size, spectral response characteristics, etc. Let's explain the related knowledge of industrial camera frame rate：

Frame rate (Frame rate) is a measure used to measure the number of displayed frames. The so-called measurement unit is the number of frames per second (Frames per Second), referred to as FPS or "Hertz" (Hz).　　

Due to the special physiological structure of the human eye, if the frame rate of the image being viewed is higher than 16fps, it will be considered to be coherent. This phenomenon is called persistence of vision. This is why the movie film is shot frame by frame and then played quickly.

The number of frames per second (fps) or frame rate indicates the number of times the graphics processor can update per second while processing a field. High frame rate can get smoother and more realistic animation. Generally 30fps is acceptable, but increasing the performance to 60fps can significantly improve the sense of interaction and realism, but generally speaking, it is not easy to notice a significant improvement in fluency when it exceeds 75fps. If the frame rate exceeds the screen refresh rate, it will only waste graphics processing power, because the monitor cannot be updated at such a fast speed, so the frame rate exceeding the refresh rate is wasted.

Maximum frame rate (Frame Rate)/Line Rate: the rate at which the camera collects and transmits images. For area scan cameras, it is generally the number of frames collected per second (Frames/Sec.), and for line scan cameras, it is collected per second. The number of rows (Hz).

The relationship between camera frame rate and exposure time：

Someone asked why when we use industrial cameras, after increasing the camera's exposure time, the camera's frame rate drops, and the drop is severe. What is the relationship between the camera's frame rate and exposure? If you want to get a fixed How to set frame rate and camera exposure time? So I wrote this article, answered my friend’s question, and also used Sentech camera to do related tests. The frame rate and exposure time are the same as described in this article. The detailed principle is shown below:

Exposure and Sensor Readout

The image acquisition process on the camera consists of two distinct parts. The first part is exposure. After the exposure is completed, the second part of the Readout process is to read the data from the sensor's register and transmit it (Readout process).

Regarding the image acquisition process, there are two common methods of camera operation: "non-overlapped" exposure and "overlapped" exposure. In the non-overlapped ("non-overlapped") mode, in each image acquisition cycle, the camera must complete the entire exposure/readout process before the next image acquisition starts. As shown in Figure 1.

Fig.1 Non-overlapped Exposure

Although the "non-overlapped" mode is suitable for many situations, it is not the most effective way. In order to increase the frame rate of the camera, it is allowed to read out and transmit the image data obtained in the previous frame when the next frame of image starts to be exposed. The way the camera "overlapped" exposure is shown in Figure 2.

From Figure 2 we can see that the camera read out the data and the exposure of the next frame begins to overlap. At the same time, the camera performs two operations, resulting in the same unit time in the "overlapped" exposure mode More pictures can be collected, that is, the frame rate of the camera is higher.

Fig.2 overlapped Exposure

From the above two figures, we can know that under the "non-overlapped" exposure mode and the "overlapped" exposure mode, there is a relationship between the period of a frame of image: In the "overlapped" exposure mode: FramePeriod ≤Exposure Time + ReadoutTime

In "non-overlapped" exposure mode: FramePeriod> Exposure Time + Readout Time

Take STC-A202A as an example：

It can be seen from the Spec that its Pixel Frequency is: 36.8181MHz, so the time of 1Clock is 1/36.8181Mhz = 27.3836ns, then we look at the camera's Timing chart, first look at HorizontalTiming, as shown in Figure 2:

2 Horizontal Timing

From Figure 2, the information we can read from it is 1 CLK=27.1605 nseconds, which is similar to the time we calculated from the Pixel Frequency obtained from the spec. Scanning 1Horizontal requires 1920CLK, that is, 1H =27.1605*1920 =52148.16ns=52.14816us

Next, look at the camera Vertical Timing as shown in Figure 3:

Figure 3 Vertical Timing

From Figure 3, the information we can read is 1H=52.1482useconds, which is the same as the time of horizontal Scanning calculated by Figure 2. In one frame of image, 1252H needs to be scanned, where Effective Pixels is 1220H, which is 1 In the frame image, the effective Pixels Read out time is 1220*52.1482 =63620.804us =63.620804ms, a VD signal, the time used is: 1252*52.1482=67793.5464us =67.7935464ms. According to our previous theory, the time of one frame of image in one cycletime is: Frame Period = Exposure Time + Readout Time

And we know that the frame rate of STC-A202A is 15fps, that is, 1 Frame Period = 1/15 = 66.7ms.

So in the "non-overlapped" exposure mode, ExposureTime = Frame Period – Readout Time =66.7ms -63.6ms =3.1ms. In this mode, if the exposure time exceeds 3.1ms, the frame rate will be higher than the standard frame rate 15fps is low.

If the Readout Time of 1 camera is 66.7ms, that is, the data transmission time is A, A=66.7ms, the exposure time is B, B=5ms, then the time of one frame of image is C, then C=A+B=66.7ms + 5ms = 71.7ms, then the frame rate of this camera: 1000/71.7 = 13.94FPS, then the frame rate of this camera is 13.94.

Note: In general, if the frame rate of our camera is 15fps, it means that the time of the camera's ReadOut data is 1000ms/15 = 66.7ms