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Grablink Quickpack ColorScan: Image acquisition and pre-processing for RGB line-scan inspection
Grablink Quickpack ColorScan : Image acquisition and pre-processing for RGB line-scan inspection

Quickpack is the Euresys line of products providing the most appropriate image acquisition and a set of hardware accelerated processing functions. This line of products offers, in a quick way, the right solution to a dedicated application. Grablink Quickpack Colorscan acquires high-resolution images from Camera Link RGB line-scan cameras. It provides on its FPGA the image pre-processing functions necessary for color scanning applications. These functions are executed with a much higher speed than on a PC sparing the processing power of the computer. Color document scanning or PCB inspections are then considerably eased and accelerated providing on the fly enhanced images ready for further processing. ColorScan offers scan-delay compensation, shading correction, look-up table transformation and white balance functions.

  • Acquisition from one RGB line-scan Camera Link camera
  • Base configuration up to 60 MHz
        Maximum processing rate: 50 MPixel/s (150 MB/s)

  • Image pre-processing functions accelerated by the FPGA
        Scan-delay compensation
        Shading correction
        Look-up table transformation
        White balance

  • Output formats: RGB 24- and 32-bit packed, RGB 24-bit planar
  • Form factor: 64-bit 66 MHz Desktop PCI
  • System connector: isolated inputs for line and page triggers

Color line-scan acquisition
Grablink Quickpack Colorscan acquires images from one RGB line-scan Camera Link camera. Two kinds of RGB imagers are supported: trilinear and 3-CCD. ColorScan is used with a single Camera Link?compliant camera in a 24-bit RGB Base configuration. The maximum Camera Link clock rate is 60 MHz. The Grablink Quickpack Colorscan processes the data at a maximum rate of 50 MPixel/s (150 MB/s).

Raw acquired image
Raw acquired image
Image pre-processing functions accelerated by the FPGA
Scan-delay compensated image
Scan-delay compensated image
Scan-delay compensation Scan-delay compensation
A trilinear color camera captures the luminance information at three light wavelength ranges from three distinct locations. A gap between these lines analyzed in red, green and blue is resulting due to the sensor geometry and the optical arrangement. The scan-delay compensation offered in Quickpack ColorScan gathers the color information coming from three different locations in order to reconstruct consistent RGB information.

Scan-delay compensated and shading corrected image
Scan-delay compensated and shading corrected image
Shading correction
During an acquisition, shading correction is required to compensate for lighting spatial nonuniformity, lens defects and sensor response defects. This process is carried out through the acquisition of two reference profiles, a white reference profile and a black reference profile, during a calibration phase. Quickpack ColorScan includes a shading correction applied on the fly on each of the three color components. After the calibration phase, the six profiles are compiled into the frame grabber hardware to correct the distortions. This correction is handled applying a multiplicative -- gain -- and an additive -- offset -- correction to each pixel issued in the scanned signal. This processing drastically improves the quality of the acquired images facilitating the application processing.

Look-up table transformer Look-up table transformer
A look-up table (LUT) transformer allows a dynamic transformation of a digital signal according to a pre-defined law. Quickpack ColorScan includes three LUT transformers, modifying each RGB color component after shading correction. The LUT process involves the creation of a mapping table assigning to each input value a programmable output value. The LUT device offers a great flexibility leaving the user free to define its own table contents or providing means to automatically generate LUT contents. The LUT capability included within Grablink Quickpack Colorscan offers the following setup methods: exhaustive definition of the transformation law, parametric shaping of the transformation law through a few intuitive controls, white balance by RGB gain correction implemented as special transformation laws.

Scan-delay compensated, shading corrected and white balanced image
Scan-delay compensated, shading corrected and white balanced image
White balance
Grablink Quickpack Colorscan is able to manage white balance correcting for RGB channel imbalance mainly due to differences in sensitivity of sensors, to the illumination system and due to the optical filter. After calibration, a correcting gain is then individually applied to each color channel to compensate for unbalanced R, G, and B components.


Shutterless cameras
Most high-resolution color line-scan cameras have no electronic shutter capability. Consequently, they have to be operated at a constant cycling rate in order to maintain a constant sensitivity. QuickPack ColorScan implements a unique downweb resampling feature* yielding a defined aspect ratio irrespective of web speed variations. A built-in rate converter accommodates an off-the-shelf motion encoder to control the line acquisition process, enabling any programmable aspect ratio, including perfect square pixels.


*Patent pending


 

 

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