Method and apparatus for producing digital images having extended dynamic ranges
First Claim
1. A method of combining a plurality of differently exposed source images of the same object or scene, the method comprising the steps of:
- a. establishing a response function characterizing the source images in terms of values of a response parameter and exposures producing the values; and
b. based on the response function, combining the source images into a composite image comprising image detail from each of the source images and having a greater range of image detail than any of the source imageswhereinc. the source and composite images each comprise an ordered array of pixels;
d. the pixels of the composite image correspond to the pixels of the source images; and
e. the images are combined by assigning, to each composite-image pixel, a pixel-parameter value representing a weighted average of the pixel parameter of corresponding pixels from the source images obtained by;
i. for each source image, generating a certainty function characterizing a tonal range of greatest image detail; and
ii. for each composite-image pixel, (A) weighing the corresponding pixels from the source images in accordance with the certainty functions, (B) combining the pixel-parameter values of the corresponding source image pixels in accordance with the weighting, and (C) assigning the combined pixel-parameter value to the composite-image pixel.
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Abstract
Different exposures of an electronically represented, pictorial scene are combined into a final image having expanded dynamic range yet still capturing subtle differences in exposure. The final image provides increased shadow, midtone and highlight detail notwithstanding the limited response of the system (electronic or photographic) that produced the component images. The invention features automatic identification of optimally exposed regions (on a pixel-by-pixel basis) from the component images, as well as automatic combination into a final image. The invention may also be used to make a camera, of possibly unknown response function, behave as an array of photometric measurement instruments (e.g., an array of light meters) to within a constant scale factor.
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Citations
16 Claims
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1. A method of combining a plurality of differently exposed source images of the same object or scene, the method comprising the steps of:
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a. establishing a response function characterizing the source images in terms of values of a response parameter and exposures producing the values; and b. based on the response function, combining the source images into a composite image comprising image detail from each of the source images and having a greater range of image detail than any of the source images wherein c. the source and composite images each comprise an ordered array of pixels; d. the pixels of the composite image correspond to the pixels of the source images; and e. the images are combined by assigning, to each composite-image pixel, a pixel-parameter value representing a weighted average of the pixel parameter of corresponding pixels from the source images obtained by; i. for each source image, generating a certainty function characterizing a tonal range of greatest image detail; and ii. for each composite-image pixel, (A) weighing the corresponding pixels from the source images in accordance with the certainty functions, (B) combining the pixel-parameter values of the corresponding source image pixels in accordance with the weighting, and (C) assigning the combined pixel-parameter value to the composite-image pixel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus for combining a plurality of differently exposed source images of the same object or scene, the apparatus comprising:
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a. analysis means for establishing a response function characterizing at least one of the source images in terms of values of a response parameter and exposures producing the values; b. combining means for combining, based on the response function, the source images into a composite image comprising image detail from each of the source images and having a greater range of image detail than any of the source images; and c. a computer memory for storing images as ordered sets of pixels each having at least one associated pixel parameter; wherein d. the analysis means establishes a response function characterizing at least one of the source images in terms of values of a pixel parameter and exposures producing the values, and is configured to generate, for each source image, a certainty function characterizing a tonal range of greatest image detail; and e. the combining means is configured to (i) weight the corresponding pixels from the source images in accordance with the certainty functions, (ii) combine the pixel-parameter values of the corresponding source image pixels in accordance with the weighting, and (iii) store the combined pixel-parameter value in the computer memory as a displayable value. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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Specification