# Image Quality Assessment of Digital Image Capturing Devices for Melanoma Detection
## 1 Introduction  
Melanoma is a malignant tumour that arises from melanocytes and involves primarily the skin. Melanomas are usually heavily pigmented but can also be amelanotic. Even small melanomas may tend to metastas, leading to a relatively unfavourable prognosis, and account for 90% of skin cancer deaths [1]. Dermoscopy was added to the clinical examination in the nineties as a noninvasive tool to improve diagnostic ability [2]. Dermoscopy, or dermatoscopy, uses a handheld microscope called a dermoscope or dermoscope, that is equipped with a magnification lens and a light source. It facilitates visualisation of subsurface skin structures otherwise not visible to the unaided eye [3]. Today, dermoscopy is an integrative part of the clinical examination, adding significantly to the early detection of skin cancer [2]. Total body photography (TBP) and dermoscopy make it possible to detect a melanoma very early in its evolution, while decreasing the number of unnecessary biopsies and improving recognition of atypical lesions [4, 5]. In skin imaging, capturing colour accurately isa necessary [6]. Colours for melanin range from black and brown to grey and blue, depending on the location of the melanin within the skin layers, in terms of depth [3]. Even a hard-to-detect hue difference could make a significant difference in melanoma diagnosis [7]. Photographs are invaluable in dermatologic diagnostics, management, research, teaching, and documentation tools [8; 9]. Dermatologists specialised in skin cancer use TBP and dermoscopy routinely for melanoma detection [10; 11]. However, the use of technological aids for melanoma detection by dermatologists in general practice and primary care physicians has been slow, due to cost and inconvenience [4]. This is changing due to the mobile revolution, as smartphone-based digital cameras and dermoscopes enter the professional market [4; 12]. Because of the difference in technologies, different imaging devices can produce different results [8; 9]. The proliferation of dermatologic imaging has evolved without the benefit of dermatology specific Digital Imaging and Communications in Medicine (DICOM) standards as exist for other medical specialities. The lack of standards for dermatologic imaging undermines the quality and usefulness of skin lesion imaging [4; 8; 9]. In both the medical and public realms, all will benefit from the development of three categories of standards that help to ensure quality (spatial resolution, colour accuracy, clarity of focus), privacy, and interoperability [4]. Therefore, considering the rapid improvements in digital imaging technologies and ubiquity of digital imaging in our society, it is of the utmost importance to standardise the use of digital imaging in dermatology [9]. In our study, we focus on measurement of the most significant image quality parameters, including sharpness, spatial resolution and colour reproduction, recommended as assessment measures for clinical expertise [8; 13; 14]. The standardised quantitative image measurements methods were applied for the image quality parameters analysis. We analysed data measured from images captured with different smartphones or high-resolution cameras used by dermatologists, to compare them with the results of a state-of-the-art digital dermoscopy system. Spatial resolution and image sharpness are some of the basic and frequently discussed characteristics of digital imaging devices. An imaging system can distinguish fine details of an image. For conventional digital cameras, standards such as ISO 12233 exist [15], which define a reference target and an evaluation method used for measuring both sharpness and resolution. The spatial frequency response (SFR), analogous to the modulation transfer function (MTF) of an optical imaging system, is one of the measurements for analysis of spatial resolution defined in ISO 12233. Resolution and image sharpness are important and frequently discussed features of a digital dermoscopy system, and can be measured [7; 8; 9; 10; 11; 16; 17].