Apparatus and method for high dynamic range imaging using spatially varying exposures
First Claim
1. A system for high dynamic range imaging comprising:
- an image sensor comprising an array of light-sensing elements, the image sensor sensing an image of a scene and providing corresponding pixel values representing light intensities impinging on respective ones of the light-sensing elements, the image sensor providing a saturated pixel value when the intensity of light impinging on a corresponding one of the light-sensing elements is greater than a first threshold level and providing a blackened pixel value when the intensity of light impinging on a corresponding one of the light-sensing elements is below a second threshold level, the image sensor having a low dynamic range relative to the range of intensities of the image of the scene;
a mask interposed between the scene and the array of light-sensing elements of the image sensor, the mask having a multiplicity of light-transmitting cells that attenuate the intensity of scene light transmitted through the mask on to the light-sensing elements, wherein the light-transmitting cells are configured so that the intensity of scene light transmitted on to the light sensing elements is attenuated by brightness level amounts that vary spatially across the array of light-sensing elements, and whereby the scene is exposed to the light sensing elements in a spatially varying manner, each of the light-sensing elements having a corresponding exposure value indicative of the transparency of the cells through which light impinging on the light-sensing element passes, the transparency of each of the cells of the mask being alterable by applying a respective exposure control signal to the mask;
a mask controller coupled to the image sensor for receiving the pixel values provided thereby and for computing, and applying to the mask, exposure control signals for minimizing the number of saturated pixel values and blackened pixel values from the image sensor, and providing exposure values corresponding to the applied exposure control signals; and
an image processor coupled to the image sensor for receiving the pixel values provided thereby, the image processor comprising a normalizer for mapping the pixel values by a function of the exposure values to derive corresponding normalized pixel values.
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Abstract
Apparatus and methods are provided for obtaining high dynamic range images using a low dynamic range image sensor. The scene is exposed to the image sensor in a spatially varying manner. A variable-transmittance mask, which is interposed between the scene and the image sensor, imposes a spatially varying attenuation on the scene light incident on the image sensor. The mask includes light transmitting cells whose transmittance is controlled by application of suitable control signals. The mask is configured to generate a spatially varying light attenuation pattern across the image sensor. The image frame sensed by the image sensor is normalized with respect to the spatially varying light attenuation pattern. The normalized image data can be interpolated to account for image sensor pixels that are either under or over exposed to enhance the dynamic range of the image sensor.
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Citations
48 Claims
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1. A system for high dynamic range imaging comprising:
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an image sensor comprising an array of light-sensing elements, the image sensor sensing an image of a scene and providing corresponding pixel values representing light intensities impinging on respective ones of the light-sensing elements, the image sensor providing a saturated pixel value when the intensity of light impinging on a corresponding one of the light-sensing elements is greater than a first threshold level and providing a blackened pixel value when the intensity of light impinging on a corresponding one of the light-sensing elements is below a second threshold level, the image sensor having a low dynamic range relative to the range of intensities of the image of the scene;
a mask interposed between the scene and the array of light-sensing elements of the image sensor, the mask having a multiplicity of light-transmitting cells that attenuate the intensity of scene light transmitted through the mask on to the light-sensing elements, wherein the light-transmitting cells are configured so that the intensity of scene light transmitted on to the light sensing elements is attenuated by brightness level amounts that vary spatially across the array of light-sensing elements, and whereby the scene is exposed to the light sensing elements in a spatially varying manner, each of the light-sensing elements having a corresponding exposure value indicative of the transparency of the cells through which light impinging on the light-sensing element passes, the transparency of each of the cells of the mask being alterable by applying a respective exposure control signal to the mask;
a mask controller coupled to the image sensor for receiving the pixel values provided thereby and for computing, and applying to the mask, exposure control signals for minimizing the number of saturated pixel values and blackened pixel values from the image sensor, and providing exposure values corresponding to the applied exposure control signals; and
an image processor coupled to the image sensor for receiving the pixel values provided thereby, the image processor comprising a normalizer for mapping the pixel values by a function of the exposure values to derive corresponding normalized pixel values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27)
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28. A method for high dynamic range imaging comprising the steps of:
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exposing an image sensor to light from a scene to sense an image frame, a wherein the image sensor comprises an array of light sensing elements;
interposing a mask between the scene and the array of light-sensing elements of the image sensor, the mask having a multiplicity of light-transmitting cells that attenuate the intensity of scene light transmitted through the mask on to the light-sensing elements, the transparency of each of the cells of the mask being alterable by applying a respective exposure control signal to the mask;
applying exposure control signals to the light-transmitting cells so that the intensity of scene light transmitted on to the light sensing elements is attenuated by brightness level amounts that vary spatially across the array of light-sensing elements, and whereby the scene is exposed to the light sensing elements in a spatially varying manner, each of the light-sensing elements having a corresponding exposure value indicative of the transparency of the cells through which light impinging on the light-sensing element passes, the image sensor sensing the spatially varying exposure image and providing corresponding pixel values representing light intensities impinging on respective ones of the light-sensing elements, the image sensor providing a saturated pixel value when the intensity of light impinging on a corresponding one of the light-sensing elements is greater than a first threshold level and providing a blackened pixel value when the intensity of the light impinging on a corresponding one of the light-sensing elements is below a second threshold level, the image sensor having a low dynamic range relative to the range of light intensities of the image of the scene; and
normalizing the pixel values provided by the image sensor with respect to the spatially varying exposure of the scene by the light-sensing elements to derive corresponding normalized pixel values. - View Dependent Claims (24, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43)
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44. A method for high dynamic range imaging comprising the steps of:
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exposing a frame of photographic film to an image of a scene through a mask having a multiplicity of light transmitting cells controlling the exposures of respective regions of the film to light from the scene, each of the respective regions of the film having a corresponding exposure value indicative of the transparency of the masked cell through which light impinging on the region passes;
storing the exposure values corresponding to the respective regions of the film;
processing the film to develop a masked image contained thereon or on a print thereof;
scanning the processed film or a print thereof with an image scanner to derive pixel values corresponding to the respective regions of the film or a print thereof; and
normalizing the pixel values from the scanner using the stored exposure values to derive normalized pixel values. - View Dependent Claims (45, 46, 47, 48)
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Specification