Method of detecting global motion and global motion detector, and digital image stabilization (DIS) method and circuit including the same

• US 9,025,885 B2
• Filed: 03/14/2013
• Issued: 05/05/2015
• Est. Priority Date: 05/30/2012
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Alpert, Sharon, Jeong, Yowon, Govrin, Omri
• Primary Examiner(s): Carter, Aaron W
• Application Number:
  US13/830,631
• Publication Number:
  US 20130322766A1
• Time in Patent Office: 782 Days
• Field of Search: 382/197, 382/236, 382/253, 348/208.99, 348/208.4, 348/208.13, 375/240.16
• US Class Current: 382/197
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/198 including smoothing of a sequence of encoding parameters, e.g. by averaging, by choice of the maximum, minimum or median value
• CPC Class Codes: H04N 19/521 for estimating the reliability of the determined motion vectors or motion vector field, e.g. for smoothing the motion vector field or for correcting motion vectors
• CPC Class Codes: H04N 19/527 Global motion vector estimation

Abstract

Disclosed is a global motion detecting method which includes receiving a video sequence of input images, calculating local motion vectors, one for each image block of a current input image, grouping image blocks of the current input image into image block groups, calculating a group motion parameter of each of the image block groups based on local motion vectors of the image blocks in each respective image block group, and determining a global motion parameter of the currently input image according to the group motion parameters.

Claims

1. A global motion detecting method comprising:

receiving a video sequence of input images;

calculating local motion vectors, one for each image block of a current input image;

grouping image blocks of the current input image into image block groups based on local motion vectors of the image block groups;

calculating a group motion parameter of each image block group among the image block groups based on the local motion vectors of its respective image blocks; and

determining a global motion parameter of the current input image based on a selected one of group motion parameters of the image block groups,

wherein the grouping image blocks into image block groups comprises grouping the image blocks into the image block groups having the same size according to predetermined group size information.

2. The global motion detecting method of claim 1, wherein the group motion parameters of the image block groups are calculated by performing random sample consensus based on local motion vectors of the image blocks in the respective image block groups.

3. The global motion detecting method of claim 1, wherein the determining the global motion parameter of the current input image comprises:

iteratively judging whether differences between the group motion parameters of each pair of image block groups are larger than a threshold value, and

if a difference between two group motion parameters of the two image block groups of the pair is smaller than the threshold value, then expanding a size of an image block group such that image block groups having a difference between their group motion parameters below the threshold value are grouped into one expanded image block group, and calculating a group motion parameter of the expanded image block group; and

if a difference between the group motion parameters of the two image block groups of the pair is larger than the threshold value, then selecting the global motion parameter based on selecting one group motion parameter from among the group motion parameters of the image block groups.

4. The global motion detecting method of claim 3, wherein the iteratively judging whether differences between the group motion parameters of each pair of image block groups are larger than a threshold value comprises:

projecting a specific point of the current input image onto a virtual image according to each of the two group motion parameters respectively; and

comparing the distance between two specific points that are respectively projected onto the virtual image according to the two group motion parameters, with the threshold value.

5. The global motion detecting method of claim 4, wherein the expanding of sizes of the image block groups is performed according to mean shift mode seeking.

6. The global motion detecting method of claim 3, wherein the selecting the global motion parameter based on selecting one group motion parameter from among the group motion parameters comprises:

projecting first feature points of the current input image onto a virtual image according to the group motion parameters respectively;

calculating a distance distribution between second points of a previous image input prior to the current input image, which correspond to the first feature points respectively, and the first points projected onto the virtual image; and

selecting a group motion parameter where a distribution of the calculated distance distribution over a first rate is below a first threshold value, as the global motion parameter.

7. The global motion detecting method of claim 6, wherein the first rate is 95%.

8. The global motion detecting method of claim 6, further comprising:

selecting a dominant motion parameter from among the group motion vectors of the image block groups if the difference between the group motion parameters of the image block groups is larger than the threshold value.

9. The global motion detecting method of claim 8, wherein the selecting a dominant motion parameter comprises:

selecting a group motion parameter where a distribution of the calculated distance distribution over the first rate is larger than the first threshold value and smaller than a second threshold value, as the dominant motion parameter.

10. The global motion detecting method of claim 1, further comprising:

detecting a jitter noise motion component of the global motion parameter for performing digital image stabilization of the input image based on the determined global motion parameter.

11. The global motion detecting method of claim 1, further comprising:

detecting a Pan-Tilt-Zoom (PTZ) component of the global motion parameter for performing frame rate conversion of the input image based on the determined global motion parameter.

18. The global motion detecting method of claim 4, wherein the expanding of the image block groups is performed according to mean shift mode seeking.

12. A global motion detector circuit comprising:

a local motion vector calculator configured to calculate the local motion vector of each image block of an input image;

a grouping unit configured to group the image blocks into image block groups;

an initial group size register configured to provide an initial size of the image block groups to the grouping unit;

a random sample consensus calculator configured to calculate a group motion parameter of each of the image block groups based on the local motion vectors of its image block groups; and

a determination unit configured to determine the global motion parameter based on the group motion parameters,

wherein if a difference between two of the group motion parameters among pairs of the group motion parameters is below a threshold value, the determination unit provides the grouping unit with new group size information for including image block groups corresponding to group motion parameters having a difference smaller than the threshold value,

wherein the grouping unit regroups the image blocks into expanded image block groups in response to the new group size information, and

wherein the random sample consensus calculator recalculates group motion parameters of the expanded image block groups.

13. The global motion detector circuit of claim 12, wherein if a difference between the two group motion parameters among pairs of the group motion parameters is larger than a threshold value, the determination unit projects feature points of the input image onto a virtual image according to each of the two group motion parameters respectively, calculates a distance distribution between feature points of a previous image input prior to the input image and the feature points projected onto the virtual image, and selects a group motion parameter where a specific rate of the distance distribution is below a first threshold value, as the basis for the global motion parameter of the input image.

14. A digital image stabilization (DIS) method for stabilizing a video image sequence, comprising:

receiving a video sequence of input images; and

performing a global motion parameter detecting method, wherein the global motion parameter detecting method comprises;

calculating a local motion vector of each image block of a current input image;

grouping image blocks of the current input image into image block groups based on local motion vectors of the image block groups;

calculating a group motion parameter of each image block group among the image block groups based on the local motion vectors of its respective image blocks; and

determining a global motion parameter of the current input image based on a selected one of group motion parameters of the image block groups,

wherein the grouping the image blocks into image block groups comprises iteratively expanding the image block groups to include adjacent image block groups of an initial group size, based on whether differences between two group motion parameters of each pair of image block groups is larger than a threshold value.

15. The digital image stabilization (DIS) method of claim 14, wherein the grouping the image blocks into image block groups further comprises:

initially grouping the image blocks into image block groups having the same size according to predetermined initial group size information.

16. The digital image stabilization (DIS) method of claim 14, wherein the iteratively expanding image block groups comprises:

iteratively judging whether differences between the group motion parameters of each pair of image block groups are larger than a threshold value, and

if a difference between the group motion parameters of the two image block groups of the pair is smaller than the threshold value, then expanding a size of an image block group such that image block groups having a difference between their group motion parameters below the threshold value are grouped into one expanded image block group, and calculating the group motion parameter of the expanded image block group.

17. The digital image stabilization (DIS) method of claim 14, wherein the iteratively expanding image block groups further comprises:

if a difference between the group motion parameters of the two image block groups of the pair is larger than the threshold value, then selecting one group motion parameter from among the group motion parameters of the expanded image block groups as the basis of the global motion parameter.