The PoC project FRAME has explored the possibility of developing and commercializing an optical imaging instrument with the unique ability to acquire and store several images simultaneously on a single camera detector. This new concept, which is named Frequency Recognition Algorithm for Multiple Exposures (FRAME), employs an "image-coding" strategy, where each exposure is given a unique illumination pattern. Thanks to this novel coding approach, the camera sensor may be exposed to light several times before readout is necessary – a completely new feature within the field of optical imaging. All images are stored on-chip simultaneously and can be, then, individually accessed through a post-processing decoding procedure, where each exposure is “unlocked” from its unique structural code.
The originality of the FRAME concept, is that the technique relies on the characteristics of the illumination rather than on the characteristics of the camera. Thus, four light pulses characterized by a specific modulated intensity pattern are created and illuminate the sample one after another. The length of the pulse define the exposure time and the time delay between each pulse defines the frequency at which the images are recorded.
The ability for a single detector to acquire a number of images simultaneously opens up for a variety of new measurement schemes. However, in this project, the concept has been used for high-speed videography. By using femtosecond laser pulses it has been demonstrated in 2017 that FRAME can produce series of images at a frame rate never ever reached before. However the instrument that has been developed in the PoC project uses inexpensive white LEDs instead of advanced laser systems. The compact system, allowed to record series of 4 images within a few microseconds.
Currently, expensive (~100 000 Euros) high-speed cameras can reach equivalent speeds, but at the cost of image pixel resolution. Here the proposed setup is 20% the cost of a modern high speed camera and has the potential to easily reach better performance in terms of frame rate, by using new LEDs illumination pulses within a few hundreds of nanoseconds. A prototype instrument has been created through the PoC project at LaVision GmbH, and the system has been tested to image the early liquid injection from a real world automotive injector. Series of 4 images where obtained at the rate of 200 kHz.
