Camera defocus direction estimation
AssigneeSony Corporation
InventorsJianing Wei, Alexander Berestov
Life of this patent
Estimating the term…
Abstract
Apparatus and methods for estimating defocus direction from a single image obtained, such as in a digital camera apparatus, are presented. To determine defocus direction, point spread function (PSF) differences for the image are evaluated in the frequency domain, with frequency pairs being found having largest difference in their Fourier transform magnitudes, from which a direction estimate feature is extracted, and defocus direction estimated based on relation of estimated feature and statistics derived from camera image tests. The method can be applied for controlling autofocus mechanisms in cameras, or other applications requiring rapid determination of defocus directions, such as from a single image.
Claims20
An apparatus for determining defocus direction from an image, comprising:
- (a) a processor configured for processing an image which has been captured from an image capture element or device;
- and
- (b) programming executable on said processor for determining defocus direction of the image, said processing comprising:
- (i) partitioning the image into blocks;
- (ii) converting a spatial image function of each said block of the image into a frequency domain function, and convolving with a point spread function (PSF) while finding frequency pairs in the PSF with largest differences in transform magnitude;
- (iii) averaging transform magnitudes at the same radial distances to their origins, thus converting a two dimensional frequency domain function into a one dimensional frequency domain function;
- (iv) determining one or more pairs of local minimums in the one dimensional frequency domain function;
- and
- (v) determining a frequency difference feature as a ratio between radial components of the transform within said one or more pair of minimums to indicate in-front or behind position of the image in relation to a correct focus position for that image.
An apparatus for determining defocus direction from an image, comprising:
- (a) a processor configured for processing an image which has been captured from an image capture element or device;
- and
- (b) programming executable on said processor for determining defocus direction of the image, said processing comprising:
- (i) partitioning the image into blocks;
- (ii) converting a spatial image function of each said block of the image into a frequency domain function, and convolving with a point spread function (PSF) while finding frequency pairs in the PSF with largest differences in transform magnitude;
- and
- (iii) averaging transform magnitudes at the same radial distances to their origins, thus converting a two dimensional frequency domain function into a one dimensional frequency domain function;
- (iv) determining one or more pairs of local minimums in the one dimensional frequency domain function;
- and
- (v) determining a frequency difference feature as a ratio between radial components of the transform within said one or more pair of minimums to indicate in-front or behind position of the image in relation to a correct focus position for that image, performed in response to a statistical process estimating distribution of the difference feature on training images.
A method of determining defocus direction from an image, comprising:
- (a) partitioning an image into blocks within a device configured for video processing;
- (b) converting a spatial image function of each said block into a frequency domain function, and convolving with a point spread function (PSF) while finding frequency pairs in the PSF with largest differences in transform magnitude;
- (c) averaging transform magnitudes at the same radial distances to their origins, thus converting a two dimensional frequency domain function into a one dimensional frequency domain function;
- (d) determining one or more pairs of local minimums in the one dimensional frequency domain function;
- and
- (e) determining a frequency difference feature as a ratio between radial components of the transform within said one or more pair of minimums to indicate in-front or behind position of the image, as a defocus direction, in relation to a correct focus position for at least one target within that image;
- (f) wherein said defocus direction of the image indicates whether the image was captured either in-front of a focus plane for a target object, or behind the focus plane of that target object.
Dependencies are inferred from the claim text.