Photographers will always have the artistic license to claim that motion blur was their intention. But machine vision use cases such as imaging-based automatic inspection, quality control and code reading in factory automation and logistics require ultimate sharpness of any acquired images.
It’s not a question whether there is motion or not; there is only the question about the speed (v) of the motion and the challenge of capturing an image with the sharpness required.
A pixel blur less than or equal to one pixel is the best approach to freezing motion. You can achieve this by reducing the exposure time (tE), either by controlling the camera’s shutter, the strobe duration of a flash or both. See Equation 1:
where tE is the necessary exposure time to achieve one pixel of blur for a given size of the field of view (FOV) and number of pixels (NP). FOV and NP are both in the direction of motion of the object’s speed of motion (v), see Figure 1.
Let’s establish an example:
Plugging these values into Equation 1 gives you:
It’s now up to you to find a way to generate a light pulse (strobe) with a tE equal to or less than 3.µs. Keep in mind some applications may require a shorter exposure time due to a higher speed of the moving object.
At TI, we started brainstorming a design to nail down a specification and ended up with a documented hardware sample. At the top of our wish list was the ability to drive light-emitting diodes (LEDs) with strobe durations down to 1 µs. The LEDs had to be driven with a programmable closed-loop controlled constant current. We also wanted some nice-to-have features, like support for high frame rates, a wide input-voltage range and a trigger interface. We ended up with the LED Lighting Control Reference Design for Machine Vision, shown in Figure 2.
The LED-lighting control reference design features:
The reference design is divided into sub-blocks representing the different functions. We implemented some uncommon approaches to achieve this complete feature set, which I discuss in this post.
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