Method and device for aligning a plurality of digital pictures

1. A method for aligning a plurality of first digital pictures, each first digital picture comprising a plurality of pixels wherein each pixel is associated with a pixel value, the method comprising:

generating, by a processor, a second digital picture for each first digital picture,

wherein generating the second digital picture for the first digital picture comprises determining, for each of a plurality of pixels of the first digital picture, a number representing the pixel values of pixels in a neighborhood of the pixel relatively to the pixel value of the pixel;

assigning, by a processor, the number as a pixel value to a pixel of the second digital picture corresponding to the pixel of the first digital picture;

generating, by a processor, aligning parameters based on the plurality of second digital pictures; and

aligning, by a processor, the plurality of first digital pictures based on the aligning parameters;

wherein determining, for each of a plurality of pixels of the first digital picture, a number representing the pixel values of pixels in the neighborhood of the pixel relatively to the pixel value of the pixel comprises

determining a relative value for each pixel of the pixels in the neighborhood of the pixel based on comparison of the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel; and

determining the number representing the pixel values of the pixels in the neighborhood of the pixel relatively to the pixel value of the pixel based on the determined relative values;

wherein determining a relative value for each pixel of the pixels in the neighborhood of the pixel based on comparison of the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel comprises

determining a difference between the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel; and

comparing the difference with a threshold value;

wherein the threshold value is determined based on a comparagram which is a two-dimensional joint histogram between a reference first digital picture and a target first digital picture of a plurality of first digital pictures.

2. The method according to claim 1 , wherein when the difference is larger than the threshold value, the relative value is determined to be a first pre-determined value.

3. The method according to claim 1 , wherein when the absolute value of the difference is smaller than or equal to the threshold value, the relative value is determined to be a second pre-determined value.

4. The method according to claim 1 , wherein when the difference is smaller than opposite of the threshold value, the relative value is determined to be a third pre-determined value.

5. The method according to claim 1 , wherein the number representing the pixel values of the pixels in the neighborhood of the pixel relatively to the pixel value of the pixel is determined to be sum of the relative value for each pixel of the pixels in the neighborhood of the pixel.

6. The method according to claim 5 , wherein each relative value is weighed differently.

7. The method according to claim 1 , further comprising: determining, for each pixel value of the reference first digital picture, a majority pixel value in the target first digital picture mapping from the reference first digital picture based on the comparagram.

8. The method according to claim 1 , wherein the threshold value is determined based on a histogram for the target first digital picture.

9. The method of claim 1 , wherein generating the second digital picture for the first digital picture comprises normalizing the exposure of the first digital picture and generating the second digital picture based on the first digital picture with normalized exposure.

10. The method of claim 9 , wherein the exposure of the first digital picture is normalized by a bidirectional intensity mapping function.

11. The method of claim 1 , wherein generating the second digital picture for the first digital picture comprises reducing the size of the first digital picture and generating the second digital picture for the first digital picture with reduced size.

12. The method according to claim 1 , wherein the aligning parameters comprises translation in a first direction, translation in a second direction, and rotation angle, wherein the first direction is orthogonal to the second direction.

13. The method according to claim 12 , wherein the aligning parameters are approximated using Taylor series.

14. The method according to claim 12 , wherein generating the aligning parameter of translation in the first direction and the aligning parameter of translation in the second direction comprises generating reduced density second digital pictures.

15. The method according to claim 12 , wherein generating the aligning parameter of rotation angle comprises determining, for each second digital picture, a histogram in a first direction and a histogram in a second direction for each second digital picture, the first direction being orthogonal to the second direction.

16. The method according to claim 1 , wherein aligning the plurality of first digital pictures starts from the first digital pictures which have relatively low saturation.

17. A device for aligning a plurality of first digital pictures, each first digital picture comprising a plurality of pixels wherein each pixel is associated with a pixel value, the device comprising:

a first generator, comprising at least one processor, configured to generate a second digital picture for each first digital picture,

wherein generating the second digital picture for the first digital picture comprises determining, for each of a plurality of pixels of the first digital picture, a number representing the pixel values of a plurality of pixels in a neighborhood of the pixel relatively to the pixel value of the pixel;

an assigning unit, comprising at least one processor, configured to assign the number as a pixel value to a pixel of the second digital picture corresponding to the pixel of the first digital picture;

a second generator, comprising at least one processor, configured to generate aligning parameters based on the plurality of second digital pictures; and

a aligning unit, comprising at least one processor, configured to align the plurality of first digital pictures based on the aligning parameters;

wherein determining, for each of a plurality of pixels of the first digital picture, a number representing the pixel values of pixels in the neighborhood of the pixel relatively to the pixel value of the pixel comprises determining a relative value for each pixel of the pixels in the neighborhood of the pixel based on comparison of the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel; and

determining the number representing the pixel values of the pixels in the neighborhood of the pixel relatively to the pixel value of the pixel based on the determined relative values;

wherein determining a relative value for each pixel of the pixels in the neighborhood of the pixel based on comparison of the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel comprises

determining a difference between the pixel value of the pixel and the pixel value of the pixel in the neighborhood of the pixel; and

comparing the difference with a threshold value;

wherein the threshold value is determined based on a comparagram which is a two-dimensional joint histogram between a reference first digital picture and a target first digital picture of a plurality of first digital pictures.