What is time-delay integration?

When imaging fast-moving objects, it is a challenge to capture an image with a sufficient signal level while maintaining minimal motion blur or image smear. Designed to solve this issue, Time-Delay Integration (T⁣D⁣I⁣) is a specialized readout mode optimized to image fast-moving objects with increased sensitivity compared to traditional snapshot imaging.

While T⁣D⁣I⁣ C⁣C⁣D⁣s⁣ have existed since the 1970s, Nüvü Camēras’ is the first manufacturer to integrate this technology to the E⁣M⁣C⁣C⁣D⁣, which features significantly lower noise and faster readout rates.


T⁣D⁣I⁣ allows capturing images of moving objects at very high speeds or in low light levels. In typical C⁣C⁣D⁣s⁣, charges are accumulated on the sensor during exposure and the whole frame is transferred and read out at once to make the image available. However, if the object moves during exposure, the signal is spread out over multiple pixels which creates blurring. Even in cameras adapted for scanning applications, such as line-scan C⁣C⁣D⁣s⁣, this means exposure time must be short to preserve image quality. As such, a line-scan C⁣C⁣D⁣ needs high light levels to be able to capture sufficient signal for a high-quality image quickly enough to avoid blurring.

T⁣D⁣I⁣ overcomes the limitation on illumination levels by shifting the image on the sensor as it is being integrated, to follow the movement of the target. On C⁣C⁣D⁣s⁣, signal charges on each line of the sensor are transferred vertically to the readout area. T⁣D⁣I⁣ synchronizes this transfer with the movement of the object; this mitigates blurring since signal charges on the sensor follow the target object. As a result, the effective exposure time of the target lasts as long it is in the field of view of the camera. The more vertical lines the C⁣C⁣D⁣ sensor has, the longer the effective integration.

time-delay integration schematics


For the T⁣D⁣I⁣ technique to be successfully implemented, the signal charges must be transferred in the same direction and at the same relative speed as those of the object to be imaged. This is often handled by the use of external triggering for the camera synchronized with the movement of the object.

Due to the synchronized transfer of lines across the whole sensor, in T⁣D⁣I⁣ mode the time-base of the imaging is referenced to the line rate rather than to the frame rate. Hence, the exposure time is set as the exposure time per line, and the external trigger input controls the read-out of single lines of the ribbon. In essence, the image output by a T⁣D⁣I⁣ camera has a fixed horizontal size but an unlimited vertical size. The effective exposure time for the image is equal to the number of vertical pixel lines of the C⁣C⁣D⁣ times the exposure time per line. It’s also relevant to note that there is no downtime between frames in T⁣D⁣I⁣ mode.