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Optical and visual metrics
Published in Pablo Artal, Handbook of Visual Optics, 2017
The term performance is used to cover all aspects of an imaging system on its ability to perform a specific task. We talk about optical performance to refer to the efficacy or achievement with which the optical system produces good images. The term image quality is used in a more restrictive sense to describe the fineness of detail that can be resolved in the image or the similarity between the image and their corresponding object. On the other hand, visual performance is defined by the speed and accuracy of processing visual information (CIE 2011), that is, by how well a visual task, for example, spatial vision, can be performed by a subject.
Borate Phosphors for Neutron Radiography
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
To a first approximation, the “image quality” can be described in terms of the “signal-to-noise ratio of the image (S/N)”. This will improve with the exposure time. There are three factors that contribute to the noise level; i) the stochastic processes going on during the detection itself (shot noise), ii) that from the readout process (readout noise) and iii) from background effects as dark current or random effects from background radiation (dark noise). These factors will differ from system to system. Which factor becomes decisive also likewise depends on the specific system.
Noise Removal Techniques in Medical Images
Published in Siddhartha Bhattacharyya, Anirban Mukherjee, Indrajit Pan, Paramartha Dutta, Arup Kumar Bhaumik, Hybrid Intelligent Techniques for Pattern Analysis and Understanding, 2017
Noise represents redundant information which degrades the image quality. The type of noise present in the image plays an important role in the denoising process of the image and hence the image quality improves after denoising. Medical images are often corrupted by various types of noise during its acquisition or transmission process. The noises such as Gaussian noise, speckle noise, Poisson noise, and salt-and-pepper noise are the most common noises that corrupt medical images.
Control-based event-driven bandwidth allocation scheme for video-surveillance systems
Published in Cyber-Physical Systems, 2022
Gautham Nayak Seetanadi, Karl-Erik Årzen, Martina Maggio
The cameras in the network are adaptive in nature and regulate their bandwidth utilisation by encoding the captured images. Images captured directly by the camera are large in size and unsuitable for direct transmission. The size of images after encoding them is dependent on the encoding technique used and the amount of compression decided by the quality factor. Image quality denotes the amount of information retained in the image after encoding with a higher quality generally leading to a clearer image but with a large frame size. The resulting frame size is also dependent on the artefacts in the images captured, arising due to lighting, movement, nature among others [3–5], leading to variation in sizes for images encoded with the same quality factor.
Influence of floating-ring-electrode on large-aperture liquid crystal lens
Published in Liquid Crystals, 2018
Che-Ju Hsu, Jyun-Jia Jhang, Jia-Cih Jhang, Chi-Yen Huang
The image performance of the 125 μm-thick 2-FREE LALC lens was observed using the setup described as follows. Three different objects, namely, dice, cat doll, and dog doll, were placed behind the 2-FREE LALC lens at distances of 16, 19, and 97 cm, respectively. A CCD camera with lens module was placed in front of and close to the LALC lens cell to capture the formed images of the object. A polariser with a transmission axis parallel to the rubbed direction of the LALC lens cell was attached on the CCD camera. When the FREE LALC lens is addressed at 10 V, the focal length of the FREE lens is 18.5 cm. this setup captures the clear image of the dog doll situated 97 cm behind the lens [Figure 9(a)]. As the applied voltage is switched to 22 V, the focal length of the FREE LALC lens is tuned to 17.5 cm, and the clear image of the cat doll situated 19 cm behind the lens was captured [Figure 9(b)]. The observed results indicate that the 2-FREE LALC lens still preserved well lens function at low voltages, even though the flat phase profile appears in the AH centre. By regulating the voltage to 40 V, the focal length of the FREE lens further decreases to 16.5 cm. The clear image on the dice situated 16 cm behind the lens was captured [Figure 9(c)]. A slight focus shift (approximately 2 cm) of the 2-FREE LALC lens makes the camera lens module achieve wide focus range (approximately 81 cm), indicating the high adaptability of the FREE LALC lens in an optical system. Notably, the image quality is affected by many conditions, such as scattering of the cell, colour dispersion of the LC material, ambient light, positions of the object, and quality of the used camera lens module.
Generation of enhanced information image using curvelet-transform-based image fusion for improving situation awareness of observer during surveillance
Published in International Journal of Image and Data Fusion, 2019
The visual analysis of the resultant fused images is a subjective evaluation method. For further validation of the results after subjective evaluation, statistical analysis of the fused images is also carried out. The statistical analysis of fused images is an objective evaluation method to assess fused image quality. For carrying out statistical analysis, image quality evaluation metrics like standard deviation, entropy, peak signal-to-noise ratio and correlation are calculated. Each image quality evaluation metric is used to check the fused image quality in terms of its sharpness, information fidelity and losses (if any). The results of various image quality parameters are discussed below.