VALIDATION OF SPECTRAL MODEL OF DIGITAL COLOR CAMERA FOR IMAGE PROCESSING IN COLOR-VISION BASED OPTICAL CORRELATION-EXTREME AIRCRAFT NAVIGATION SYSTEM

The spectral mathematical model of a digital color camera as an opto-electronic device was designed in the process of algorithms development for color optical correlation-extreme navigation system of unmanned aerial vehicles. The model includes the relative spectral camera sensitivity for three color channels (“red”, “green” and “blue”) and the photosensitive cell charge accumulation calibration model. Both models were successfully developed and described in the earlier publications. This paper presents integral validation of these components as a mathematical model of the device for the use in optical correlation- extreme navigation systems image processing. The additive error of such model should be less than 15–20% of the dynamic measurement range. During the experiment, a sample of 24 reference objects spectrograms was collected, and their photo was taken by the studied camera under constant lighting conditions. The decoded color coordinates of the “raw” photo information averaged for each object and reduced to the linear scale with the radiometric calibration model were used as the reliable data generated by the camera. The spectrograms processed by the spectral sensitivity model were used as the output values of its mathematical model. The determination coefficient R² was used as a mathematical model quality metric. Its value was equal to 0.98 in the worst case (for the “blue” color channel), and the additive error distribution appeared to be close to normal. Hence the conclusion can be drawn that the model explains data variability under the impact of random factors as reliable as possible with the use of a single independent variable. The average additive error in the unit dynamic range of measurements was equal to 0.014 with a standard deviation of 0.029. Such parameters meet the advanced requirements and prove that the developed mathematical model validation is successful. Applying the developed model makes it possible to correct the color of the current images according to light spectra while the photo is taken or synthesize images of objects in the ready sample photographs of the area. The supplement of the model by spectral characteristics of the atmosphere radiation absorption and scattering gives the possibility to assess the impact of these factors on the imaging process in color optical correlation-extreme navigation systems.
 

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