In order to plot the PTC, we need to find the corresponding standard deviation values (i.e., noise) for each value of the mean signal in the image S m e a n. Now, the averaged image S m e a n contains the whole dynamic range of the signal values produced by a sensor. We took K = 64 images (matrices S 1 … S K of size N × M pixels) of such a gradient input scene, and averaged the images to reduce temporal noise, producing the matrix S m e a n of size N × M pixels. Table 1: Parameters of the simulated CMOS sensor (taken from the manufacturer’s specifications). The measurements were conducted at room temperature ( + 25 ∘C) if not stated otherwise. For the numerical model, the uniform image was used that corresponds to the light signal of the LEDs. The measurements were performed for monochromatic light with wavelength λ = 0.55 μ m ( we assume for the same of simplicty that the light is monochromatic, and therefore we need the spectral response of the sensor at one wavelength λ = 0.55 μ m). For example, in case of estimation of the radiometric function, the flat field for the hardware sensor was generated by an array of LEDs. The methods and procedures of the measurement were the same for the hardware and the simulated photosensor. The paper addresses the issue of the lack of comprehensive high-level photosensor models that enable engineers to simulate realistic effects of noise on the images obtained from solid-state photosensors. Experimental results that confirm the validity of the numerical model are provided. Procedures for characterisation from both light and dark noises are described. An example of the simulated CMOS photosensor and a comparison with a custom-made CMOS hardware sensor is presented. The formulated model can be used to create synthetic images for testing and validation of image processing algorithms in the presence of realistic images noise. The model also includes voltage-to-voltage, voltage-to-electrons, and analogue-to-digital converter non-linearities. The model includes photo-response non-uniformity, photon shot noise, dark current Fixed Pattern Noise, dark current shot noise, offset Fixed Pattern Noise, source follower noise, sense node reset noise, and quantisation noise. A high-level model of CCD and CMOS photosensors based on a literature review is formulated in this paper. In many applications, such as development and testing of image processing algorithms, it is often necessary to simulate images containing realistic noise from solid-state photosensors.
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