In the field of Machine Vision, Line Scan cameras are widely adopted in applications that demand high speed, high precision, and large inspection coverage, such as roll-to-roll material processing, high-precision semiconductor manufacturing, and PCB inspection.
Why Do Industrial Line Scan Applications Need HDR?
In real-world applications, engineers often encounter the following challenge:
the object under inspection consists of composite materials with significantly different surface reflectivity.
Due to the large differences in reflectivity between materials—such as the green solder mask and solder pads on a PCB—a single lighting condition cannot properly accommodate both materials at the same time.
If multiple light sources are activated simultaneously, they tend to interfere with each other, making it difficult to achieve lighting conditions that satisfy all inspection requirements.
As a result, the most common workaround is to set up separate inspection stations, each optimized for a specific lighting condition.
However, this approach comes with several major drawbacks:
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Low inspection efficiency
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High hardware cost
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Large factory floor space requirements
These disadvantages significantly reduce the competitiveness of the inspection machine or system.
This is a typical scenario in industrial inspection where Line Scan combined with HDR becomes essential.
The Purpose of HDR (High Dynamic Range)
The purpose of HDR is to preserve complete image detail across highlights, shadows, and mid-tones within a single image.
For industrial inspection, HDR performance directly affects several key factors:
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Whether defects on materials with different reflectivity can be captured without overexposure or underexposure
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Whether edges are sufficiently defined for reliable image processing and software detection
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Whether inspection performance remains stable despite product variation
When two HDR exposure levels are insufficient to fully cover product variability, three, four, or even more intensity levels may be required to achieve robust and stable inspection results.
This is precisely where Line Scan strobe (flash) technology becomes critical.
Why Traditional HDR Does Not Work for Line Scan Cameras
In Area Scan cameras, HDR is typically implemented by capturing multiple images at the same position using different exposure times or lighting intensities, then merging them via software.
However, Line Scan imaging operates fundamentally differently, making traditional HDR methods unsuitable:
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Line Scan images are generated line by line. When the object is in continuous motion, it is impossible to capture multiple exposures at the same physical position.
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The object cannot be stopped to re-capture images under different lighting conditions.
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Capturing different lighting conditions at different encoder positions will compromise geometric accuracy and result in image distortion.
In short, Line Scan HDR must be completed in real time at each encoder position, without affecting line speed or geometric precision.
The Optimal Solution for Line Scan HDR: Strobe Lighting (Strobe HDR)
For industrial Line Scan HDR applications, the most stable and mature solution is:
Under Encoder / Trigger-based scanning, strobe lighting intensity and/or camera exposure time are rapidly switched to capture multiple images with different brightness levels required for HDR. These images are then merged into a single HDR image through real-time software or FPGA-based processing.
Application Example: PCB Inspection
In PCB inspection, the system must simultaneously perform:
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Green solder mask surface inspection
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OCR character inspection
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Solder pad / pad surface inspection
Opticks, in collaboration with German patented technology, utilizes FPGA-based real-time precise strobe timing control. Using a color Line Scan camera (2-line or 3-line) and two lighting fields, the system captures three brightness levels at each encoder position:
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Light Source A
Optimized to provide sufficient brightness for inspecting the green solder mask
(Solder pads are overexposed)
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Light Source B
Optimized to generate sufficient contrast between OCR characters and the green solder mask
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Light Source A + B
Optimized to prevent overexposure on solder pads, clearly revealing surface conditions
- These three images form the base data for Line Scan HDR synthesis. Through FPGA/software-based HDR algorithms, they are merged into a single HDR image.
The following video demonstrates this application in practice.
During high-speed scanning, Opticks’ proprietary Line Scan technology captures three Line Scan images with different brightness levels in real time:
https://youtu.be/AMMLO5AmrTY
When deployed on actual production lines, this technology delivers significant advantages:
✔ No impact on existing production line speed
✔ Multiple inspection tasks completed within a single inspection station, significantly improving efficiency and reducing factory footprint
✔ Reduced optical and system cost — inspection setups that previously required three separate stations can now be consolidated into one
Typical Applications for Line Scan Strobe HDR
Line Scan Strobe HDR is well suited for applications involving complex materials, large reflectivity differences, product variation, and multiple lighting requirements, including:
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Surface defect inspection of heterogeneous composite materials
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Semiconductor packaging and wafer inspection
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PCB / FPC AOI inspection
Conclusion: Line Scan HDR Must Be Solved from the Lighting Level
In industrial vision systems, Line Scan HDR is not merely an image post-processing feature. It is a comprehensive system design that integrates:
Line Scan Camera × Strobe Lighting × FPGA Timing Control × HDR Algorithms
Opticks has successfully deployed this technology in multiple customer systems over many years, with long-term stability consistently validated in real production environments.
Even in high-speed inspection scenarios involving materials with drastically different reflectivity, this solution enables inspection systems to reliably acquire high-quality HDR images and achieve stable, repeatable inspection performance.
Opticks will continue to share in-depth industrial vision technologies and practical implementation insights, helping customers build reliable, scalable, and production-ready automated inspection systems.