What are Readout Modes in Image Sensors?

Explain Sensor Readout Modes?

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- GoPhotonics

Nov 7, 2023

Readout modes are methods used to obtain data from a sensor by recording the emitted photons. Image sensors are crucial components of contemporary electronics and are employed in a wide range of applications to detect and quantify physical properties including temperature, light, pressure, and more. Image sensors have multiple readout modes, each with their own specific characteristics. It is important to choose the proper readout mode for a particular sensor in order to receive precise results. ITR (Integrate Then Read), IWR (Integrate While Read), and IMRO (Internal Multi-Row Readout) are the most important readout modes employed in sensors.

Integrate Then Read out mode

Integrate Then Readout (ITR) mode, is a type of readout mode used in some sensors, especially those that measure continuous physical quantities. In this mode, the sensor integrates light for a predetermined amount of time, then periodically reads out the charge that has accumulated, which is the integrated value. This reduces read noise but, if the scene is not perfectly motionless, this can also cause motion blur. This can be useful in situations where the measurement rate is slow or when the measurement has a low signal-to-noise ratio.

The integration is typically performed using an analog-to-digital converter (ADC) that samples the sensor signal at regular intervals and combines the samples to create a digital value. In most cases, the integration time and sample rate are configurable, which allows the user to decide the measurement precision and measurement speed.

The integrated value can then be obtained from the sensor by periodically polling it or by utilizing an interrupt mechanism to alert the sensor that a new value is available. 

In ITR mode, the signal of frame N integrated in the input stage is read out after the end of the integration time of frame N and the integration of the signal of frame N+1 starts after all the signals of frame N have been read out.

Advantages of ITR

Compared to other readout modes, the ITR method has a number of benefits. First, by integrating the measurement over time, it can increase the signal-to-noise ratio, enabling the sensor to pick up weaker signals. Second, since the integrated value can be delivered at a slower rate than the raw measurement, it can lower the measurement rate needed by the sensor. Finally, ITR mode can be useful in applications where the measurement rate is slow, such as scientific experiments or remote sensing.

Integrate While Readout mode

Integrate While Readout (IWR) mode is a type of readout mode used in sensors to measure continuous physical quantities. In this method, the physical quantity is continuously integrated by the sensor, which outputs the integrated value simultaneously. This results in less motion blur but higher read noise and is frequently employed in situations involving high light levels or powerful signals such as high-speed imaging, motion detection, and industrial control applications.

In IWR mode, the signal of frame N integrated in the input stage is read out during the integration time of frame N+1. 

Advantages of IWR

Integrate While Readout mode has several advantages over other readout modes. First, it provides real-time output of the integrated measurement, allowing the sensor to continuously monitor the physical quantity. Second, it can reduce the memory requirements of the sensor, as the integrated value does not need to be stored in an internal memory. Finally, Integrate While Read out mode can be useful in applications where the measurement rate is fast, such as high-speed imaging or motion detection.

Internal Multi-Row Readout mode 

Internal Multi-Row Readout (IMRO) mode refers to the sensor's readout architecture. It is found on high-end digital cameras when the image sensor reads out multiple rows of pixels simultaneously. This speeds up the data flow, cuts down on the amount of time it takes to take an image, and is used to improve image quality. As a result, there may be reduced image noise, a greater dynamic range, and higher frame rates.

Advantages of IMRO

One of the key advantages of IMRO is that it delivers improved image quality with less noise and improved color accuracy. Another advantage is the increased speed it provides. The faster readout speed allows for faster frame rates. 


The readout mode used will depend on the specific requirements of the application and the capabilities of the sensor and system. Different readout modes in sensors serve different purposes and are useful in different applications. When choosing a readout mode, it is important to consider the requirements of the application, such as measurement accuracy, measurement rate, and data transmission rate. ITR is commonly used in a variety of applications, including scientific experiments, remote sensing, and industrial inspection. IWR is employed in applications, including high-speed imaging, motion detection, and industrial control. IMRO is used for capturing fast-moving subjects.