Geometric Distortion Correction from Novacam

Geometric distortion exists when the spatial relationship between the pixels in the image do not equate to the spatial relationships between corresponding points in the scene. The amount of distortion will vary for different imaging devices, but some distortion will always exist due to imperfection in optical design and configuration.
Novacam’s Geometric Distortion Correction software can be used in many applications including microscopy, panoramic cameras, machine vision metrology, and many others. Correction algorithms are implemented in C/C++ and are currently used on PC and DSP platforms for moderate frame rates. To increase the processing speed, they can be programmed into FPGAs. Geometric correction is performed in two steps: calibration and application of the correction.


Geometric Distortion Correction from Novacam

The Correction Table Builder
The Correction Table Builder is used during the imaging system calibration phase. Calibration is done for each unit. The builder uses an image obtained from a dot-phantom surface (a grid of equally spaced points) to create the position correction table. Depending on the application, an additional image obtained from a uniformly lighted surface can be used to improve the correction.
Intensity Correction
An intensity correction module can be used in order to provide a uniform light sensibility over the entire imaging system’s field of view.
Framing
A framing module can be used to format the output images: region of interest, resolution and pixel depth, etc.


The sample or reconstructed dot-phantom images are shown before and after application of Novacam's correction modules.


Calibration
Calibration must be performed before the first usage of the imaging system or every time it is suspected that its distortion characteristics have changed. During the calibration step, an image of a phantom covering the system's field view is acquired. The Correction Table Builder is then used to compare the distribution of calibration dots on the image with their theoretical position and to generate a table of polynomial correction coefficients.
Applying the correction
Application of the correction table is done in real time for each acquired image. Novacam's Geometric Distortion Correction software provides correction of any spatial distortion over the entire imaging system’s field of view. Processing time and resources are minimal, since most processing has been done during the calibration phase, and the correction is performed using the ready data tables created with the Correction Table Builder.


Calibration and image acquisition process
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