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Tech Papers

Extended Depth of Focus (EDoF) Tuned in Real-Time

by Razor-Sharp Results - Silicon Software GmbH

Silicon Software in partnership with Optotune, has created an enhanced “Extended Depth of Focus” (EDoF) functionality using a focus tunable lens for real-time operation. From a continuous image acquisition sequence of up to 20 (currently) individual frames with varying focal length, a sharp final image with an expanded range of focus is generated in real-time. At the center of the FPGA-based image processing system, alongside the lens, is a programmable frame grabber equipped with the EDoF application and with a CoaXPress interface. Both companies have successfully presented this system at several events.

The core of the image processing system is the electronic, focus tunable EL-10-30-Ci lens from Optotune, which is mounted in front of the camera and passes through various focal lengths in a step by step fashion by electrically altering the liquid lens’ shape. Prior to this technological combination, calculating the final sharp image in such series of image frames within the time demands of industrial applications was a bottleneck that was very difficult to alleviate. This system, developed together with Silicon Software, enables faster image acquisition at a rate of 20 images in 50 milliseconds and delivers the generated image in real-time together with a depth/index image as well as a contrast image. To achieve this result, the demonstration system is comprised of a monochrome JAI Spark SP-5000M-CXP2 with 2-channel CoaXPress interface that achieves a total bandwidth of 12.5 Gbit/sec at 5-megapixel resolution and a very high frame rate.

The entire system is controlled by Silicon Software’s microEnable 5 marathon VCX-QP frame grabber with a graphically programmable FPGA, which in turn has a 4-channel CoaXPress interface as camera inputs, 2 GB on-board RAM storage as internal image processing storage, and DMA1800 technology, based on PCIe x 4 Gen2 for image transfer to the host-PC storage. In the frame grabber’s FPGA, the image is calculated with the expanded focus range from the image stack it receives. The EDoF application, programmed with the VisualApplets graphical development environment, executes the image calculation and output as well as synchronous control of the Gardasoft TR-CL180 lens controller and the camera. The lens controller dynamically alters the lens focus within milliseconds.

Sharp EDoF Image Calculated

The EDoF application running on the frame grabber’s FPGA controls image acquisition consisting of 20 individual images each, set between 1 to 4 diopters, with an image frequency of 400 fps. The 20 images of varying sizes are first individually geometrically corrected, with minimal latency, along the x- and y axes using bilinear interpolation. The application then calculates the local contrast for every pixel of the image using a high-pass filter. It calculates the point with the highest local contrast from the individual image via looping. The result is the level with the highest contrast and thus the sharpest representation. From all the sharp image points, the image processing system outputs two final images at the end: an index/depth image (depth map) with the index of the image in question with the highest local contrast and the completely sharp image.

This high-speed image processing system using a focus tunable lens is especially well suited for inspection systems with high data throughput, since the frame grabber executes the calculation in a short period of time during image acquisition. Preferred applications are PCB, semiconductor or general electronics inspection, during which the form of the object to be inspected must be calculated and reconstructed, as an example, for the testing of solder joints on circuit board components. Further applications include the inspection of deep objects or fluids, such as those in bottle production or in pharmaceuticals, where foreign particles must be identified at a 100% rate.

“The EDoF system with integrated focus tunable lens can process image stacks up to 50 individual images with deterministic latencies and high speed. The application running on the FPGA directs the lens controller, the camera and the image processing from acquisition to processing to image output”, explained Dr. Klaus-Henning Noffz, Managing Director of Silicon Software.

This video from Optotune demonstrates the image processing system and the final images:

https://youtu.be/-NBXIMhBlUQ

 

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