Exposure is the process by which an image sensor senses light. During the exposure process, photons are collected by CMOS Sensor and converted into charge. And after the exposure, the CMOS Sensor removes the charge out in a certain way.
The difference between global exposure and roller shutter exposure
The three elements that affect exposure are: aperture, shutter and sensitivity.
Aperture: Aperture is a light hole formed by overlapping small blades located inside the lens;
Sensitivity: also called ISO value, refers to the degree of sensitivity of the camera’s photosensitive element to light;
Shutter: The shutter is the device used by the camera to control the time of light hitting the photoreceptor.
There are two common ways of electronic shutter: global shutter and rolling shutter. Global shutter is realized by exposing the whole picture at the same time.
It is usually used in CMOS sensor line by line exposure.
At the beginning of exposure, the sensor will scan line by line and expose line by line until all pixels of the photoreceptor component are exposed, with a certain time difference between each line.
By exposing the whole scene at the same time.
At the beginning of the exposure, the Sensor starts collecting light at all pixels, and then at the end of the exposure, the light collection circuit is cut off. The sensor then reads out a complete image.
Global exposure and shutter exposure
The more common exposure methods of industrial cameras are global exposure and roller shutter exposure. In fact, they are named after the two shutter shutter and global shutter. What is the difference between them?
Let’s start with the simpler global exposure. That is, when the aperture is opened, the entire image chip is exposed at the same time. Therefore, the exposure time is related to the switching speed of the machinery. Since it is related to mechanical motion, there is a theoretical minimum exposure time, so the advantages and disadvantages are very obvious:
Advantage: All pixels are exposed at the same time
Disadvantages: Exposure time is limited, there is a minimum exposure time, can shoot moving objects
Rolling curtain exposure
The way of exposure of the rolling curtain may be related to the concept of the rolling curtain. The length of exposure time of the rolling curtain depends entirely on the opening size of the rolling curtain and the speed of movement of the rolling curtain. That is to say, the faster the rolling curtain moves, the smaller the distance between the rolling curtain, the smaller the exposure time of the sensor. Therefore, the shutter exposure method can have a smaller exposure time.
Advantages: Smaller exposure time
Disadvantages: line by line exposure, jelly effect, not suitable for shooting moving objects.
< Roller shutter exposure >
The jelly effect
When the industrial camera is shaking, or the photographed object is in high speed motion, the progressive scanning speed is not enough, the shooting results may appear “tilt”, “sway” or “partial exposure” and other situations, this phenomenon due to the different exposure time of the picture up and down and produce misalignment, is defined as the jelly effect.
Distortions due to the Jelly Effect
What kind of exposure does the SONY FCB-EV9500L use?
Which exposure method is used by SONY FCB-EV9500L? The FCB-EV9500L camera movement module has a 1/1.8-inch STARVIS™ CMOS Sensor, which is obviously a roll-shutter exposure. The AR anti-reflection coating minimizes the re-image/double image phenomenon, and can capture images without losing key information even in night and dark environments. With super anti-shake function; It can suppress the phenomenon of jelly effect distortion that reduces the image.