Understanding the exposure-time effect on speckle contrast measurement for laser projection with rotating diffuser
- 33 Downloads
To evaluate the influence of observer’s exposure time over speckle noise of laser displays, we developed the high-speed measurement method which can measure speckle contrast over a wide range of exposure time without adjusting the brightness of laser displays in our previous work. We attempted to observe the exposure-time effect in speckle contrast for several commercially available laser displays using this method. However, their speckle contrasts were nearly constant at various exposure times in our experiments, although it is a more reasonable argument that the speckle contrast of laser display equipped with a temporally-averaging speckle-reduction device is dependent on the exposure time. Since we assumed that the temporal averaging factors of their laser displays were underestimated, we prototyped a speckle-reduction device using an intentionally slow-rotating diffused plate and measured the speckle contrast for a laser projection applying this device in this work. The speckle contrast was increased at the lower linear velocity of the diffused plate than 3.8 mm/s when the exposure time was fixed at the human response time. And, the speckle contrast was increased in the region of short exposure time when the linear velocity was fixed at 0.12, 0.47 and 1.9 mm/s. By analyzing the cross-correlation and the speckle average grain size, we confirmed that this phenomenon was caused by the exposure-time effect. In addition, we verified the relationship between the linear velocity, the exposure time and the temporal averaging factor by comparing the measurement results with theoretical fitting function.
KeywordsSpeckle contrast Exposure time Laser Speckle-reduction device Diffused plate Linear velocity
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
- 2.Fukui, T., Ito, K., Suzuki, K., Tokita, H., Furukawa, Y., Kubota, S.: Effective calibration method for absolute speckle contrast measurement. In: 1st Laser display conf. dig. tech. pap. LDC8-3, laser display conference, Yokohama: (2012)Google Scholar
- 4.Fukui, T., Suzuki, K., Kubota, S.: speckle contrast measurement in arbitrary observation distance. In: Proc. IDW’13, PRJ4-1, 1251–1254, Sapporo (2013)Google Scholar
- 6.Fukui, T., Suzuki, K., Kubota, S.: Speckle measurement of laser display by means of simulating to human eye perception. In: Proc. IDW’14, PRJ3-2, 1094–1097, Niigata: (2014)Google Scholar
- 7.The Illuminating Engineering Institute of Japan: Hikari No Keisoku Manual (Light Measurement Manual), p. 404. Nihon Riko Shuppankai, Tokyo (1990) (in Japanese)Google Scholar
- 9.Suzuki, K., Kubota, S.: Understanding the exposure-time effect on speckle contrast measurement for laser projection with rotating diffuser. In: 7th Laser display and lighting conf. dig. tech. pap. LDCp9-11, laser display and lighting conference, Yokohama (2018)Google Scholar
- 10.Xu, M., Shi, Y., Tang, G., Liu, J., Chen, X.: Speckle characterization in laser projector display. World academy of science, engineering and technology. Int. J. Math. Comput. Phys. Electri. Comput. Eng. 6(3), 261–264 (2012)Google Scholar
- 12.Kuwata, M., Sasagawa, T., Kojima, K., Michimori, A., Sugiura, H., Hirano, Y., Endo, T.: Reducing speckle in laser displays with moving screen system. J. Image Inform. Telev. Eng. 65(2), 224–228 (2011) [in Japanese]Google Scholar
- 15.Goodman, J.W.: Speckle phenomena in optics. Roberts & Company, Colorado (2007)Google Scholar
- 16.Kinoshita, J., Takamori, A., Yamamoto, K., Kuroda, K., Suzuki, K.: Image resolution of raster-scan laser mobile projectors considering color speckle effects. In: 7th laser display and lighting conf. dig. tech. pap. LDC6-2, laser display and lighting conference, Yokohama (2018)Google Scholar