Device and method for characterization of subjective speckle formation
The invention concerns a device for characterization of subjective speckle formation, especially for quantification of the speckle contrast. The device has a projection surface ( 9 ) and a coherent or partly coherent light source ( 10 ) for projecting of an image onto the projection surface ( 9 ), a detection unit ( 11 ) for generating of speckle images ( 13 ) of the image projected onto the projection surface ( 9 ), as well as a data acquisition and analysis unit ( 12 ) for processing and evaluation of image data.
1. Method for characterization of subjective speckle formation, especially for quantification of the speckle contrast, wherein the method involves the following steps:
projecting of an image onto a projection surface by means of a coherent or partly coherent light source,
generating of speckle images of the projection surface with a detection unit, wherein exposure times (T) of the detection unit are changed in stepwise manner until an optimal exposure time (Topt), at which a speckle contrast (Cspeckle) is reduced to a maximum value,
generating of a plurality of speckle images with the optimal exposure time (Topt) and forming of an average speckle image,
generating of a plurality of images of the projection surface without projected image of the coherent or partly coherent light source with the optimal exposure time (Topt) and forming of an average dark image,
subtracting of the average dark image from the average speckle image for reduction of background illumination noise,
forming of an intensity histogram for analysis of the image quality.
2. Method according to claim 1 , characterized in that an aperture value (f) is adjusted in dependence on speckle sizes (D) occurring in the speckle image and pixel size (P) dependent on the detection unit.
3. Method according to claim 1 or 2 , characterized in that data from the speckle images is processed and evaluated in a data acquisition and analysis unit.
4. An apparatus for characterization of subjective speckle formation, especially for quantification of the speckle contrast, the apparatus comprising:
at least one processor; and
at least one memory including computer program code,
wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to:
project an image onto a projection surface by means of a coherent or partly coherent light source,
generate speckle images of the projection surface with a detection unit, wherein exposure times (T) of the detection unit are changed in stepwise manner until an optimal exposure time (Topt), at which a speckle contrast (Cspeckle) is reduced to a maximum value,
generate a plurality of speckle images with the optimal exposure time (Topt) and forming of an average speckle image,
generate a plurality of images of the projection surface without projected image of the coherent or partly coherent light source with the optimal exposure time (Topt) and forming of an average dark image,
subtract the average dark image from the average speckle image for reduction of background illumination noise, and
form an intensity histogram for analysis of the image quality.
5. The apparatus according to claim 4 , wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to adjust an aperture value (f) in dependence on speckle sizes (D) occurring in the speckle image and pixel size (P) dependent on the detection unit.
6. The apparatus according to claim 4 or claim 5 , wherein data from the speckle images is processed and evaluated in a data acquisition and analysis unit.
7. A non-transitory computer-readable medium encoded with instructions that, when executed in hardware, perform a process for characterization of subjective speckle formation, especially for quantification of the speckle contrast, the process comprising:
projecting an image onto a projection surface by means of a coherent or partly coherent light source,
generating speckle images of the projection surface with a detection unit, wherein exposure times (T) of the detection unit are changed in stepwise manner until an optimal exposure time (Topt), at which a speckle contrast (Cspeckle) is reduced to a maximum value,
generating a plurality of speckle images with the optimal exposure time (Topt) and forming of an average speckle image,
generating a plurality of images of the projection surface without projected image of the coherent or partly coherent light source with the optimal exposure time (Topt) and forming of an average dark image,
subtracting the average dark image from the average speckle image for reduction of background illumination noise, and
forming an intensity histogram for analysis of the image quality.
8. The non-transitory computer-readable medium according to claim 7 , wherein an aperture value (f) is adjusted in dependence on speckle sizes (D) occurring in the speckle image and pixel size (P) dependent on the detection unit.
9. The non-transitory computer-readable medium according to claim 7 or claim 8 , wherein data from the speckle images is processed and evaluated in a data acquisition and analysis unit.