Method and system for capturing sequences of images with compensation for variations in magnification
A system for capturing sequences of digital images, including a lens, a digital sensor including a plurality of light-sensitive elements, a focusing module suitable for varying the focus of the lens on the sensor, and an electronic processing unit. The electronic processing unit is suitable for determining a variation in magnification between two consecutively captured digital images from a variation in the focus of the lens, and for determining a digital compensation for said variation in magnification. The electronic processing unit is further suitable for digitally processing at least one of the consecutively captured digital images on the basis of said predetermined compensation. The system enables compensation for visual effects resulting from changes in magnification between two consecutively captured images.
1. A method of capturing a sequence of digital images, the method comprising:
imaging a scene on a digital sensor, through a lens unit, with at least one first magnification value and at least one second magnification value, the second magnification value being different from the first magnification value and a variation between said magnification values arising from a variation in focus of the lens unit, the magnification values corresponding to a ratio between a size of the image of an object through the lens unit and an actual size of the object;
capturing a first digital image with the first magnification value;
capturing a second digital image with the second magnification value;
determining a digital compensation for the variation between said magnification values;
applying digital processing to the first digital image and/or to the second digital image, based on said determined digital compensation.
2. The method of claim 1 , wherein one or more parameters of the digital compensation for the variation in magnification are predetermined by calibration.
3. The method of claim 1 , wherein the digital compensation for the variation in magnification is determined based on digital analysis of the first digital image and/or of the second digital image.
4. The method of claim 1 , wherein the digital processing comprises applying a corrective variation in magnification to the first digital image and/or to the second digital image, based on said determined digital compensation.
5. The method of claim 1 , wherein the first digital image and the second digital image are two consecutive images in the sequence of digital images.
6. The method of claim 1 , wherein the variation in focus of the lens unit is from one image to the next for each image in the capture of the sequence of images.
7. The method of claim 6 , further comprising measuring a sharpness of each captured image, and wherein the variation in focus from one image to another comprises oscillating about a current focus reference position, the current focus reference position being additionally adjusted according to the measured sharpness.
8. A system for capturing sequences of digital images, the system comprising:
a lens unit;
a digital sensor comprising a plurality of light-sensitive elements; and
a processor, wherein the processor is configured to control a variation of the focus of lens unit on the sensor,
the processor being adapted to determine:
a variation in magnification between a first and second captured digital images, the variation in magnification arising from a variation in focus of the lens unit;
a digital compensation for said variation in magnification, the magnification corresponding to a ratio between a size of the image of an object through the lens unit and an actual size of the object; and
the processor being further adapted to apply digital processing to at least one of the two captured digital images based on said determined compensation.
9. The system of claim 8 , wherein the lens unit has a fixed focal length.
10. The system of claim 8 , wherein the lens unit has a variable focal length.
11. The system of claim 8 , wherein the processor is suitable for determining the variation in magnification by digital analysis of at least one of the two captured digital images.
12. The system of claim 8 , wherein the processor configured to control the variation of the lens unit on the sensor via an autofocusing module.
13. The system of claim 12 , wherein the processor is suitable for determining a change in position of the autofocusing module.
14. The system of claim 13 , further comprising a calibration table associating a position of the autofocusing module with a magnification value.
15. The system of claim 12 , wherein the processor is further adapted for imposing a variation in focus between two successively captured digital images.
16. The system of claim 15 , wherein the processor is adapted for imposing the variation in focus continuously during the capture of digital images.
17. The system of claim 15 , wherein the processor is adapted for imposing the variation in focus by oscillating the position of the autofocusing module about a current reference position.
18. A portable device comprising a system for capturing sequences of digital images, wherein said system comprises:
a lens unit;
a digital sensor comprising a plurality of light-sensitive elements; and
a processor, wherein the processor is configured to control a variation of the focus of the lens unit on the sensor;
said processor being adapted to determine:
a variation in magnification between a first and second captured digital images, the variation in magnification arising from a variation in focus of the lens unit, the magnification corresponding to a ratio between a size of the image of an object through the lens unit and an actual size of the object;
a digital compensation for said variation in magnification; and
said processor being further adapted to apply digital processing to at least one of the two captured digital images based on said determined compensation.
19. The portable device of claim 18 , embodied as one of a mobile phone, a computer and a digital tablet.