Scene-based method for determining focus
View Patent ↗A method and application specific integrated circuit for determining focus for an image capture system using scene content within an image, including the steps of: acquiring, from the image, image data having different focus positions; dividing the image data into sub-images; calculating a sub-image sharpness value for each sub-image; calculating an image sharpness value for each focus position using the sub-image sharpness values; plotting the sharpness values versus the focus position; fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and determining the focus of the image capture system from a point on the curve.
1. A method of determining focus for an image capture system using scene content within an image, comprising the steps of:
a) acquiring, from the image, image data having different focus positions;
b) dividing the image data into sub-images;
c) calculating a sharpness value for each sub-image;
d) calculating an image sharpness value for each focus position using the sub-image sharpness values;
e) plotting the image sharpness value versus the focus position;
f) fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and
g) determining the focus of the image capture system from a point on the curve.
2. The method of determining focus claimed in claim 1 , wherein the point on the curve is within a depth of focus relative to the image capture system.
3. The method of determining focus claimed in claim 1 , wherein the point on the curve is at a peak of the curve.
4. The method of determining focus claimed in claim 1 , further comprising the step of performing the steps a–g for each desired image prior to capturing the desired image.
5. The method of determining focus claimed in claim 1 , wherein the sub-image sharpness values are calculated from one or more equations selected from the group consisting of variances, covariances, skewness, kurtosis, energy, entropy, contrast, edges, textures, and a power spectrum of the image.
6. The method of determining focus claimed in claim 1 , wherein the image sharpness value is calculated by summing some or all of the sub-image sharpness values.
7. The method of determining focus claimed in claim 1 , wherein the image sharpness value is calculated by rank-ordering the sub-image sharpness values into high and/or low ranks and summing some or all of the highest sub-image sharpness values.
8. The method of determining focus claimed in claim 7 , wherein the number of sub-image sharpness values summed is determined from the image data.
9. The method of determining focus claimed in claim 1 , further comprising the step of rejecting data that does not meet specified criteria.
10. The method of determining focus claimed in claim 1 , further comprising the step of eliminating sub-image sharpness values prior to fitting the curve to the plot of image sharpness values versus focus position.
11. The method of determining focus claimed in claim 1 , wherein the image capture system is selected from the group consisting of a camera, a remote sensing system, an input scanner, and a document copier.
12. A method of determining focus for an image capture system using scene content from a plurality of images, comprising the steps of:
a) acquiring image data from the plurality of images, wherein the plurality of images have different focus positions;
b) dividing the image data into sub-images;
c) calculating a sub-image sharpness value for each sub-image;
d) calculating an image sharpness value for each focus position using the sub-image sharpness values;
e) plotting the sharpness value versus the focus position;
f) fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and
g) determining the focus of the image capture system from a point on the curve.
13. The method of determining focus claimed in claim 12 , wherein the point on the curve is within a depth of focus relative to the image capture system.
14. The method of determining focus claimed in claim 12 , wherein the point on the curve is at a peak of the curve.
15. The method of determining focus claimed in claim 12 , further comprising the step of performing the steps a-g for each desired image prior to capturing the desired image.
16. The method of determining focus claimed in claim 12 , wherein the sub-image sharpness values are calculated from one or more equations selected from the group consisting of variances, covariances, skewness, kurtosis, energy, entropy, contrast, edges, textures, and a power spectrum of the image.
17. The method of determining focus claimed in claim 12 , wherein the image sharpness value is calculated by summing some or all of the sub-image sharpness values.
18. The method of determining focus claimed in claim 12 , wherein the image sharpness value is calculated by rank-ordering the sub-image sharpness values into high and/or low ranks and summing some or all of the highest sub-image sharpness values.
19. The method of determining focus claimed in claim 18 , wherein the number of sub-image sharpness values summed is determined from the image data.
20. The method of determining focus claimed in claim 12 , further comprising the step of rejecting data that does not meet specified criteria.
21. The method of determining focus claimed in claim 12 , further comprising the step of eliminating sub-image sharpness values prior to fitting the curve to the plot of image sharpness values versus focus position.
22. The method of determining focus claimed in claim 12 , wherein the image capture system is selected from the group consisting of a camera, a remote sensing system, an input scanner, and a document copier.
23. An application specific integrated circuit for performing the steps of:
a) acquiring, from an image, image data having different focus positions;
b) dividing the image data into sub-images;
c) calculating a sub-image sharpness value for each sub-image;
d) calculating an image sharpness value for each focus position using the sub-image sharpness values;
e) plotting the image sharpness value versus the focus position;
f) fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and
g) determining the focus of the image capture system from a point on the curve.
24. An application specific integrated circuit for performing the steps of:
a) acquiring image data from a plurality of images, wherein the plurality of images have different focus positions;
b) dividing the image data into sub-images;
c) calculating a sub-image sharpness value for each sub-image;
d) calculating an image sharpness value for each focus position using the sub-image sharpness values;
e) plotting the image sharpness value versus the focus position;
f) fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and
g) determining the focus of the image capture system from a point on the curve.
25. A computer storage medium having instructions stored thereon for causing a computer to perform the method of claim 1 .
26. A computer storage medium having instructions stored thereon for causing a computer to perform the method of claim 12 .
27. A computer storage medium having instructions stored thereon for causing a computer to perform the method of claim 13 .
28. A computer storage medium having instructions stored thereon for causing a computer to perform the method of claim 14 .
29. A computer storage medium having instructions stored thereon for causing a computer to perform the method of claim 18 .
30. The application specific integrated circuit according to claim 24 for performing the step of calculating the sub-image sharpness values by rank-ordering the sub-image sharpness values into high and/or low ranks and summing some or all of the highest sub-image sharpness values.
31. The application specific integrated circuit according to claim 24 for performing the step of calculating the sub-image sharpness values by summing some or all of the sub-image sharpness values.