# Image Quality Assessment of Digital Image Capturing Devices for Melanoma Detection
## 3 Results
### Results of Colour Measurements
#### 3.2.2 Colours in the Dermoscopy Image
The \(\Delta E\) colour distance values for calibrated cameras (manual mode setting) is shown in Table 5. Columns five, six and seven present the mean \(\Delta E_{mean}\), minimum \(\Delta E_{min}\) and maximum \(\Delta E_{max}\) on measured skin colours after application of a device calibration. The result shows a significant improvement in colour constancy, where colours are much closer to the range of human eye detection capability. Practical interpretations of \(\Delta E\) colour errors can be found in the works of [PERSON] et al. [48] and [PERSON] et al. [49]. Colour errors in video and printing standards are expected between 5 and 6, between 6 and 10 the quality is still sufficient, and above ten as insufficient [48]. The mean colour error value \(\Delta E_{mean}\) for the iPhone and Huawei P10 camera models fulfil the criteria of [PERSON] et al. [48]; however, results for the Canon EOS M10 and the Samsung S10 exceeded the recommended value of [PERSON] slightly. The parameters of the Fotofinder Medicam 1000s were measured only in a default camera setting, as the manufacturer does not allow any corrections of camera parameters by the user. The \(\Delta E_{mean}\) colour difference values measured from the FotoFinder's Medicam 1000s images in-camera default mode are high. Consequently, the resulting images appear overexposed, and the colours are so visually different from the reference colour that they are evident to the naked eye. Uncorrected images were imported into the Premiere CC Software to monitor them in a vectorscope view. A vectorscope monitor displays the colour values in the image. The angle of the pixel represents the hue, and the distance out from the centre represents the amount of saturation. Pixels at the centre of the vectorscope are grey, and the colour hue starts with red in the top left, and, rotating clockwise, transitions to magenta, to blue, to cyan, to green, to yellow, and, finally, back to red. Figure 10a illustrates reference colours, presented in the vectorscope with dots. Dots of reference colours are aligned precisely on the skin tone line, between the Red (R) colour channel and the Yellow (\(\Upsilon\)) colour channel. Figure 10b show dots presenting colours from the captured image on the Medicam 1000s. The position of dots is now shifted into the yellow section, but on the line. The uncorrected microscopic image of a mole captured on the same camera is presented in Figure 11a. The colour correction was applied to improve the colours on the image, as shown in Figure 11b. The distribution of colours in the corrected image is shifted toward the reference line, as shown in the vectorscope in Figure 11b. Figure 10: Colours are presented in the vectorscope as dots. (**a**) Dots are aligned on the “skin tone line” presenting the reference value of the skin tone colours, and (**b**) dots presenting colours in the image if the reference colours were captured on the Medicam 1000s camera. For essential subjective evaluation, we verified the effectiveness of the camera calibration process on a set of dermoscopy images. We compared images that were captured with the same camera, which works in automatic or manual mode. Dermoscopy images of the same lesion were captured on the Fotofinder Medicam 1000s, Canon EOS M10, and iPhone 7 cameras. The results in Table 5 show that the most optimal result in manual mode with \(\Delta E_{man}=9.1\) was achieved by the iPhone 7 and the Canon M10 \(\Delta E_{man}=11.3\) was the highest measured colour error after calibration was applied. Figure 12 shows examples of dermoscopy images before and after calibration. Figure 12 shows a dermoscopy image captured with a Fotofinder Medicam 1000s, and Figure 12 shows an image after a colour correction performed with a software tool. Figure 12c,e show images captured on the Canon EOS M10 and iPhone 7 in automatic camera mode, and Figure 12d,f show modified images captured after camera calibration.