EMVA 1288 compliant interpolation algorithm By Jörg Kunze, Basler
B
asler has invented an interpolation algorithm, called the Virtual Pixel Interpolation, which creates values
of virtual pixels at given positions and with a common given size, thereby fulfilling all EMVA 1288 requirements for real pixels. Tis allows an easy replacement of old CCD cameras with new CMOS cameras, without changing the optical setup or soſtware of the application. Te availability of many CCD image sensors
is limited in time and volume. Te latest CMOS image sensors offer high pixel count and great image quality, but they are oſten not one-to-one replacements for CCDs, because the pixels are generally smaller. Tis means replacing a CCD camera with a CMOS model could require costly changes in application optics and soſtware. Basler’s virtual pixel interpolation serves as a
technological base for a one-to-one replacement of a CCD camera by a CMOS camera sensor. It creates images consisting of virtual pixels of the same size as the replaced CCD image sensor, complying with EMVA 1288.
The virtual pixel
interpolation algorithm runs well even on a small 8-bit controller and enables real- time application
To emulate a CCD sensor image with 5.6μm pixels using an image taken by a new CMOS sensor with smaller pixels of 3.6μm, for example, basically requires creating an image with lower resolution. Sub-sampling and binning lower the image
sensor resolution, but both methods only work for integer factors in horizontal and vertical resolution. Tis isn’t normally the case for the ratio between CCD and CMOS pixel sizes. Interpolation is a well-known technique to change the resolution of camera images; nearest-neighbour, (bi-) linear, and (bi-) cubic interpolation are oſten used. However, interpolated images frequently raise concerns in the machine vision community, because state-of-the-art interpolations can create pixels of different sizes and gain factors. Aſter one year of research, Basler identified
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The new camera image in Fig. 4c matches the ICX618 image in Fig. 4b well, whereas the IMX287 image in Fig. 4a clearly differs in field of view. The same findings hold true when zooming into the details. Also, the histogram of IMX287 in Fig. 4g is clearly different from the original ICX618 histogram in Fig. 4h, whereas the ICX618 Replacement Sensor shows a perfect match in Fig. 4i.
an efficient computable solution. Te virtual pixel interpolation algorithm runs well even on a small 8-bit controller and enables real-time application. Tis is mandatory for machine vision applications. A two-dimensional virtual pixel
interpolation has been tested on the ICX618 CCD raw image series for different resolutions. An EMVA 1288 report has been created for each resolution. All of the EMVA 1288 reports contained plausible results that were exactly as expected for a CCD image sensor with the respective pixel size. All QE values are exactly as expected within a small error bar and equal the original ICX618 QE value for the used wavelength. Te Basler AcA640-121gm is the first
CCD replacement camera incorporating this technology. Further 1:1 CCD replacement camera models are expected in the near future. Te camera has been directly compared to two conventional Basler Ace cameras, one containing an original ICX618 CCD and the other containing an IMX287 CMOS. Te latter has been proposed by Sony as successor for the ICX618. All three cameras have been tested in an optical lab using identical lenses and target scenes at different lighting conditions and different wavelengths. Te replacement is cost-efficient and easy;
no further changes in application optics, mechanics, or soſtware are expected. Tis saves cost in development, production and logistics for re-designs of vision machines.
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