[Japan successfully developed projection optical compensation technology to transform the wall into a display screen] Technology introduction

The optical compensation technology that can use patterned walls as a projector screen has been successfully developed by the research team of Japan's National Institute of Informatics Assistant Sato IMARI and Tokyo University lecturer Yoichi Sato. When projecting an image with a projector on a patterned wall, the pattern on the wall usually appears in the image, but if this new technology is used, the influence of the pattern can be eliminated, which can be reduced compared with the original method. The saturation phenomenon of brightness such as 'bleaching' and 'whitening' and the decrease of contrast. If this technology is applied to a projector, there is no need to prepare a special screen or wall. The research team said that in the future, it can also be used with small portable projectors to use the walls and desktops around them as screens.
　　 The trial-produced system can only compensate for pictures. This system consists of an LCD projector and a digital camera. A personal computer is used for compensation. The pre-correction to read the screen characteristics takes about 30-40 minutes, and the compensation of a picture takes a few seconds to tens of seconds. The team said that to achieve the requirement of processing 30 images per second when playing images, it can be achieved through a dedicated image processing circuit.

Figure 1: Screen with patterns
Figure 2: Without compensation, the screen pattern appears in the projected image

Figure 3: After compensation, the screen pattern on the projected image is not easy to see; compared with the image without compensation (Figure 2), there is almost no change in contrast, and the part without image on the screen is faintly visible The same water drop pattern as Figure 2


Figure 5: Screen with black and white stripes


　　 Generally, in order to eliminate the influence of the pattern on the screen, in order to keep the original RGB value of the projected image consistent with the RGB value of the image projected on the screen, the input image of the projector needs to be compensated. For example, when the local reflectance is reduced due to patterns, it is necessary to increase the brightness of the input image for the low-brightness pattern part, or reduce the brightness of the input image for the non-pattern part to compensate. In addition, in terms of color, either only project the compensation color to the patterned part to eliminate the pattern, or project the same color as the pattern to compensate for all parts without the pattern.
　　 But when using this method, if the brightness of the input image of the projector exceeds the output brightness limit of the projector, the parts of the original image with gradual brightness will all become white, and the phenomenon of 'whitening' will appear. The same is true for colors. For example, when the color value of red in the input image of the projector exceeds the limit that the projector can output, it seems that the red is insufficient, and the phenomenon of 'discoloration' occurs. To compensate for such low image quality by reducing the brightness of parts other than the pattern, you will face the problem of low overall image contrast.
　　 In this method, in order to correct the influence of the screen pattern while maintaining contrast, the characteristics of human vision in color gamut and brightness are used. Human vision has such characteristics, such as 'it is difficult to identify changes in brightness in high-brightness parts or low-brightness partsand many more. Therefore, when the projected image is combined with the pattern on the wall, even if there is a brightness difference or whitening phenomenon, sometimes the user will not feel it. In addition, under the premise of considering human visual characteristics, by only compensating part of the screen instead of the entire screen, it is possible to display images that make the user feel coordinated. By introducing the above method, compared with the original method, the high contrast after compensation can be maintained. However, this method is still more difficult to compensate for screens with black and white stripes or to brighten the overall darkened walls.
　　 Part of the results published this time has been published through papers. The paper has been selected as the best paper of the IEEE International Workshop on Projector Camera Systems (ProCams2006) held in June 2006, and also selected as the outstanding paper of the International Forum on Image Recognition (MIRU2006) held in July of the same year. paper.