## 5 Discussion  
By introducing a beam-splitter and an LCD panel into the system, complexity is increased. The compensation stability is greater or lesser, depending on the specification of each optical unit. The light is decreased about 50% by the beam-splitter and will be further decreased by the LCD and the OST-HMD. The light throughput of the system will be less than 10%. However, although we achieved light compensation using an HMD, the extra structure makes miniaturization harder. In further studies, we are considering using a stereo scene camera and simulating the on-axis image from that input instead of using a beam-splitter. In this study, we ignored the focus problem and forced the user perspective camera to focus on the monitor and the OST-HMD. This is one of the major reasons for the blurring of the artifact observed in Figure 10, although the artifact has been reduced from that of the existing methods [13] by using the OST-HMD to compensate colors for individual pixels. This problem needs to be better addressed to use our system in a real-life application. When seen through the LCD panel, there are some diffraction effects from the pixel grid, which is inherently caused by the property of the LCD panel used (bbs bild-und Ichitsysteme GmbH. [[http://www.bbs-bildsysteme.com/](http://www.bbs-bildsysteme.com/)]([http://www.bbs-bildsysteme.com/](http://www.bbs-bildsysteme.com/))) and might be improved by decreasing the resolution of the LCD since that does not affect the results of our method. Due to the focus problem, we can only subtract light uniformly for an entire image because pixel-wise alignment cannot be made between the LCD and the other devices. The uniform amount of light to be subtracted is decided by computing the histogram of needs percentage for the three colors of all pixels and selecting the needs percentage of the highest bin in the histogram. Although we compensated the over- or under-subtracted areas with the OST-HMD, errors may remain. Figure 11a visualizes the need for subtraction with intensity. Figure 11b,c visualize the errors that are computed as the difference between the resulting image and the target image. When \(t=33\), which is the highest needs percentage corresponding to the bright area in Figure 11a, we can get a contrast enhanced image as shown in Figure 11e, but there are errors in the green channel, on the flower area. This is likely because these pixels require a very small value for the green channel and the zero-input effect mentioned in Section 3.3.3 prevented that channel from reaching zero. When \(t=100\), with the positive compensation by the OST-HMD and color calibration, the result still had a fair contrast but lost some of the details compared to the result obtained with \(t=33\) (the yellowish part on the leaves). This indicates that a good transmittance selection policy may reduce the number of error pixels. By making it possible to calibrate and compensate for incoming light and making the image in the user's FoV reach a target image, the proposed technology can be combined with other compensation  
Figure 11: **(a)** Bright pixels are ones that need subtraction; (b) error pixels when \(t=33\), color stands for the corresponding color channel; (c) error pixels when \(t=100\); (d) simulation of \(\mathbf{I}_{T}\); (e) Simulation of \(\mathbf{I}_{U}\) when \(t=33\); and (f) Simulation of \(\mathbf{I}_{U}\) when \(t=100\). methods for CVD or even other augmented reality applications using OST-HMD where arriving light control is necessary. Conceptualization, X.M. ; methodology, Y.T., Z.Z., M.T., K.G., K.K., I.F. and X.M. ; software, Y.T. ; validation, K.K. and X.M. ; formal analysis, Y.T. ; investigation, Y.T. and K.K. ; resources, X.M. ; data curation, Y.T. ; writing--original draft preparation, Y.T. and Z.Z. ; writing--review and editing, X.M. ; visualization, I.F. ; supervision, M.T. and X.M. ; project administration, X.M. ; funding acquisition, X.M. All authors have read and agreed to the published version of the manuscript.