# Assessment and Feasibility Study of Lemon Ripening Using X-ray Image of Information Visualization
## 1 Introduction
With the advance of technology, the development of thin-film transistor (TFT) array technology, and the application of flat panel detectors (FPDs), high-resolution X-ray imaging has been quite mature [21; 22]. Multilayered monochrome grayscale images can be created based on the DICOM (Digital Imaging and Communications in Medicine) standard [23; 24], and X-ray image interpretation has been developed from intuitive interpretation to statistical interpretation based on grayscale values [25]. Monochrome is black and white. Tones of a grayscale are based on its bit depth. DICOM grayscale standard is the basis for radiography analyses. The exposure signals from the linear attenuation of the X-ray tube voltage and the absorber's density are received by the flat panel detector, which then produces signals in the form of images. If the outputs are 8-bit grayscale images, the signals are transformed into \(2^{8}\) = 256 monochrome grayscale levels according to their intensities. The images are composed of pixels of values ranged from 0 to 255. The pixel value for pure black is 0. Colors closer to white have higher grayscale pixel values. The grayscale pixel value of pure white is 255. There are systems using bit depths higher than 256 for signal sampling and display, producing 2D array radiographic grayscale images of the target object [26; 27]. Grayscale values corresponding to signal intensities are put in arrays to create grayscale images [28]. Without destroying fruits, the X-ray radiography technology can display density differences inside fruits using grayscale levels to show detailed density changes causedby insect pests, and thus identify healthy fruits and fruits with pest damages and classify them. Densities may vary with water content in fruits, hard tissues of kernels, holes caused by insect pests, hollowness, and corruption, etc. Different densities are represented by different grayscale levels [29; 30]. Currently, radiography has been applied to classification based on quality and disease detection for citrus fruits. Besides citrus fruits, X-ray radiography is extensively used for the sorting of mature lettuce heads [31], and the assessment of the ripening of mangoes [32], and tomatoes [33] based on tomography. Surface defects of fruits are often detected using color-scale analysis and radiography with appearance images of the fruits [34]. Moreover, radiography is also used in fruit quarantine. Fluoroscopy images are captured and analyzed based on color scales to mark the problematic areas [35; 36]. However, hyperspectral imaging and radiography can only be used to perform qualitative analyses for surfaces of citrus fruits. Internal ripening of citrus fruits cannot be analyzed using these methods [36; 37]. This study adopted radiography for non-destructive grayscale X-ray imaging for lemons and then performed quantitative quality analyses and comparisons based on the changes in structures and tissues using data visualization and statistical analyses, aiming to provide scientific-technical references and to expand the scope of applications of radiography.