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STANDARDS


EMVA 1288 to characterise


measurements. Terefore, release 4.0 will have two documents: ‘Release 4.0 general’ and ‘Release 4.0 linear’ – the latter as a direct successor of release 3.1.


multimodal sensors


Prof Dr Bernd Jähne, chair of EMVA 1288 and senior professor at HCI, Heidelberg University, gives a preview of release 4.0 of the EMVA standard 1288


T


he standard 1288 of the European Machine Vision Association (EMVA) is well established and used


worldwide for objective characterisation of the quality parameters for industrial cameras. Shortly, the current version, 3.1, will be replaced by release 4.0. Te new release has become necessary


because of the progress being made in image sensor technology. In the past, monochrome and colour sensors dominated the market for cameras, whereas, now, multimodal image sensors are entering the market. Tese include sensors with an extended spectral range, especially into the shortwave infrared (SWIR); multispectral sensors with more than three colour channels; polarisation sensors and time-of- flight sensors. Two other trends are of importance:


high dynamic range image sensors with a non-linear characteristic curve, and pre- processing within the camera to optimise image quality.


Release 3.1: linear characteristic curve and no pre-processing Release 3.1 of standard 1288 can only be applied to cameras with a linear characteristic curve. Furthermore, no pre- processing was possible, which changes the temporal noise, except for simple operations such as binning or time delayed integration (TDI). Tese prerequisites resulted in a simple linear camera model with just three unknown model parameters: temporal dark noise, quantum efficiency and system gain. Tese parameters can be determined


from an irradiation series measuring the linear characteristic curve and the photon transfer curve (temporal noise variance versus mean of the digital camera signal). Further application-oriented parameters


describing the quality of the camera, such as the absolute sensitivity threshold, the saturation capacity, the dynamic range and the signal-to-noise ratio (SNR) can be computed from these measurements.


New in release 4.0: abandonment of a model For a camera with a non-linear characteristic curve, the linear model of release 3.1 cannot be applied. However, a non-linear camera or a camera with pre- processing can be characterised without any model. Tis is thanks to the general system theoretical approach of the standard 1288.


‘Te new release has become necessary because of the progress being made in image sensors’


Te input signal – the number of photons


hitting a pixel during the exposure time – is known by absolute radiometric calibration. Te digital output signal and its temporal variance can be measured directly. From both, the characteristic curve and the output SNR are known. Te input SNR, which determines the


signal quality, is computed from the output SNR and the slope of the characteristic curve. Ten everything needed is known to compute the application-oriented quality parameters as with the linear model. What’s even more important is that the same measurements as with release 3.1 can be performed. Depending on the properties of the camera, either a linear model or none can be used for the evaluation of the


30 IMAGING AND MACHINE VISION EUROPE VISION YEARBOOK 2020/21


In co-operation with several member companies, EMVA has prepared an education programme with an optional certification as an EMVA 1288 expert. The first courses are already scheduled: in collaboration with Aeon, online training, on 3 and 4 November and 1 to 3 December (www. aeon.de/training_emva1288.html); and with Framos, online, on 19 and 20 May 2021 . (www.framos.com/en/company/events/ trainings/).


Comprehensive extensions In order to cope with modern image sensors, release 4.0 includes many extensions. Te most important are: • Extended wavelength range from UV to SWIR;


• Raw data of any image modality can be characterised according to the standard;


• Characterisation of the polarisation angle and degree of polarisation of a polarisation image sensor;


• Extended characterisation of non- uniformities: split in row, column and pixel non-uniformities;


• Optionally, cameras with lenses or illumination by a given exit pupil can be measured. In this way it is possible to also measure image sensors with micro lenses that are shifted towards the edge of the sensor;


• Better measure for the linearity of the characteristic curve;


• Te double-logarithmic SNR plot will be extended with measurements of the non-uniformity at all intensity steps (important for non-linear cameras).


Release 4.0 takes into consideration the rapid progress of imaging sensors. It will be possible to characterise a much wider spectrum of cameras and sensors using the standard: UV and SWIR-sensitive; multispectral; polarisation; intensified, such as EMCCDs; multilinear; and high dynamic range. Also, cameras with lenses and pre-


processing to enhance the image quality can be characterised. Despite the diversity, the quality of cameras can still be described with a minimum set of application-oriented quality parameters. Release 4.0 will be published this autumn. O


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