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System and method for producing an optically sectioned image using both structured and uniform illumination

EP2300983 B1. Filed on June 3, 2009, published on June 5, 2012. view in google patents

A first image data set of the real-world object is received at a processor where the real-world object was illuminated with substantially uniform illumination. A second image data set of the real-world object is received at the processor where the real- world object was illuminated with substantially structured illumination. A high pass filter is applied to the first-image data set to remove out-of-focus content and retrieve high-frequency in-focus content. The local contrast of the second- image data set is determined producing a low resolution local contrast data set. The local contrast provides a low resolution estimate of the in-focus content in the first-image data set. A low pass filter is applied to the estimated low resolution in-focus data set, thus making its frequency information complementary to the high-frequency in-focus data set. The low and high frequency in-focus data sets are combined to produce an optically-sectioned data set of the real-world object.

A first embodiment of the system for producing an optically sectioned image

Fig. 1 is a first embodiment of the system 100 for producing an optically sectioned image. The system 100 includes a source of illumination 105 that illuminates an object 120 to be imaged. The illumination source 105 may be a laser light, diode light, incandescent light or some other light source. For example, the optical source may be a laser beam that is used in microscopy. The object 120 to be imaged may be an in vivo cellular structure or other three-dimensional real-world object. The system also includes a pattern generator 110 that can switch the state of the illumination between uniform illumination and structured illumination. In some embodiments (e.g. Fig 1E) that use a laser illumination source, the structured illumination can be a speckle pattern. In this embodiment, the pattern generator can be a simple diffuser plate switched between a fixed state (thereby generating a fixed speckle pattern) and a rapidly moving state (thereby generating a rapidly randomized speckle pattern to mimic uniform illumination). In other embodiments (e.g. Fig. 1B), there may be more than one source of illumination and a fixed (i.e. non-switching) pattern generator may be associated with a single source. The light is directed along the optical path or paths to the real-world object. In response to the light, the real-world object generates an object signal that is directed to an imaging array 130. The imaging array 130 has a plurality of sensors for sensing the object signal. The imaging array 130 converts the object signal into a plurality of electrical signals. The electrical signals may be either digital signals or analog signals. In the case of an analog signal, the analog signal is converted to a digital signal by passing the object signal through an analog-to-digital converter. The resulting digital data set is processed in processor 140. The digital data set may then be saved for later retrieval or may be directed to a display 150 for viewing.

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A flow chart of the generalized methodology for producing an optically sectioned image using both uniform illumination and struc

Fig. 2 shows a flow chart of the process for producing an optically sectioned data set of an object for display using both uniform illumination and structured illumination. The object is exposed to uniform illumination (or illumination that has been effectively rendered uniform by randomization) and an image of the object is captured using a detector array (200). The object is also exposed to structured illumination (spatially random, patterned, speckled etc.) and an image of the object is captured with a detector array (210). The detector array may be the same or different for both the structured illumination and uniform illumination. Thus, at least two images are produced. The uniform illumination image data set is passed through a high-pass filter to extract the high-frequency component of the uniform illumination data set (220). This high-frequency component represents intrinsically in-focus data because, upon imaging, only in-focus data is highly resolved (i.e. contains high frequencies). The structured illumination data set undergoes contrast extraction (230). The contrast of the structured illumination data set becomes small for object signals that are out-of-focus. The local contrast of the imaged structure thus provides a measure of the degree to which the object is in-focus or contains in-focus elements. Techniques that can be used to measure the local structure contrast include single sideband demodulation and double sideband demodulation and other techniques to measure the local variance of data from the image data set. The local contrast data set provides a low resolution estimate of the proportion of the uniform illumination data set that is in focus. A multiplication of the local contrast data set with the uniform illumination data set thus provides a low resolution estimate of the in-focus image (240). In an alternative embodiment, steps 230 and 240 can be combined into a single step by subtracting the uniform illumination data set from the structured illumination data set and taking the absolute value. The low resolution estimate of the in-focus image is further processed by applying a low pass filter to it that is complementary to the high pass filter applied in step 220, thereby providing a low frequency in-focus data set (250). The high and low frequency data is then combined to form an in-focus data set that contains all frequencies within the bandwidth of the imaging device (260).