Digital cameras with triangulation autofocus systems and related methods

• US 7,982,794 B2
• Filed: 03/31/2009
• Issued: 07/19/2011
• Est. Priority Date: 05/11/2005
• Status: Expired due to Fees

• Current Assignee: Sony Ericsson Mobile Communications AB (Sony Group Corp.)
• Original Assignee: Sony Ericsson Mobile Communications AB (Sony Group Corp.)
• Inventors: Wernersson, Mats Göran Henry
• Primary Examiner(s): HO, TUAN V
• Application Number:
  US12/415,679
• Publication Number:
  US 20090186655A1
• Time in Patent Office: 840 Days
• Field of Search: 348/345, 348/348, 34820899-2085
• US Class Current: 348/345
• CPC Class Codes: H04N 2007/145 Handheld terminals
• CPC Class Codes: H04N 23/671 in combination with active ranging signals, e.g. using light or sound signals emitted toward objects
• CPC Class Codes: H04N 23/68 for stable pick-up of the scene, e.g. compensating for camera body vibrations
• CPC Class Codes: H04N 23/6811 based on the image signal
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors
• CPC Class Codes: H04N 23/6845 by combination of a plurality of images sequentially taken

Abstract

Digital cameras with triangulation auto focus systems include a spot beam emitter than can be used to project a spot onto a subject that is captured in an image and used to electronically automatically determine a subject to camera distance.

Claims

1. A method of auto-focusing a digital camera in still image and/or video recording mode, comprising:

projecting a plurality of discrete light spots toward a target subject using the digital camera;

capturing a first viewfinder image of the target subject with the projected light spots in response to the projecting step;

programmatically calculating a triangulation measure of distance for each of a plurality of the projected light spots in the first viewfinder image; and

automatically focusing a digital camera lens associated with the digital camera using a closest one of the calculated triangulation measure of distances.

2. The method of claim 1, further comprising:

capturing a second reference image of the target subject without projected light spots proximate in time to the capturing of the first viewfinder image;

electronically registering the first and second images;

electronically generating a difference image of pixel values obtained by subtracting pixel values from the registered first and second images; and

electronically identifying light spot locations associated with the projected light spots in the difference image,

wherein the programmatically calculating step uses the identified spot locations in the difference image to calculate the triangulation measures of distance.

3. The method of claim 2, wherein the electronically identifying step uses pixel color to identify spot location.

4. The method of claim 2, wherein the digital camera is held in a cellular telephone and comprises a circuit configured to capture the first and second images within less than about 0.067 seconds of each other, and wherein the auto-focusing step is configured to move the lens to a focused position within about 0.033 seconds after the first image is obtained to carry out the automatically focusing step.

5. The method of claim 1, wherein during the video recording mode, the method further comprises electronically patching light spots in video recording images using pixel data from corresponding locations in at least one reference viewfinder image that is devoid of light spots during video streaming to provide video recording images without light spots.

6. The method of claim 1, wherein the auto focusing step uses a camera to subject distance “

u”

that is calculated according to;

u=fs/np

where “

n”

represents a displacement measured in number of pixels in position between a light spot in the image and a center of the image, “

f”

is a focal length of the camera lens, “

s”

is a distance between the camera lens and an emitter axis for emitter(s) used to generate the projected light spots, and “

p”

is pixel pitch.

7. The method of claim 1, wherein the projecting step comprises emitting light from a light source in a visible part of a light spectrum.

8. The method of claim 2, wherein the capturing the first and second image steps are carried out using the same exposure setting and the same white balance setting.

9. The method of claim 1, wherein the projecting the light spots step is carried out by substantially concurrently projecting a plurality of discrete horizontally spaced apart spots.

10. The method of claim 2, further comprising automatically electronically correlating a region of interest in the first and second images to thereby provide image stabilization.

11. A method of auto-focusing a digital camera in a cellular telephone in still image and/or video recording mode, comprising:

projecting a plurality of spatially discrete light spots toward a target subject using the cellular telephone digital camera in a viewfinder mode;

capturing a viewfinder image of the target subject having light spots in response to the projecting step;

programmatically determining spot positions in the image;

calculating a triangulation measure of distance for each of at least a plurality of the light spots in the image;

selecting a focus distance for the camera based on a closest calculated spot distance; and

automatically focusing a digital camera lens in the cellular telephone digital camera using the selected focus distance to obtain a second image.

12. The method of claim 11, wherein the selecting step selects the focus distance from a correlation table defining different focal lengths relative to pixel location of a light spot associated with the closest spot distance in the spot image.

13. The method of claim 11, further comprising:

registering the viewfinder and second images; and

electronically subtracting corresponding pixel values in the images to generate a difference image with the spots against a dark background.

14. The method of claim 13, wherein the electronically subtracting step is repeated for all pixels in a region of interest.

15. The method of claim 13, wherein the electronically subtracting step is configured to consider pixels of different colors.

16. The method of claim 11, wherein, in the video recording mode, the method is carried out by substantially continuously repeating the steps of projecting, capturing, determining and automatically focusing, and wherein the method further comprises:

electronically patching light spots in video recording images with pixels from corresponding spot locations in at least one reference viewfinder image, the at least one reference image being devoid of light spots to thereby provide video recording images without light spots.

17. A method of auto-focusing a digital camera having a lens in a cellular telephone in still image and/or video recording mode, comprising:

(a) projecting a plurality of spatially discrete light spots toward a target subject using the cellular telephone digital camera;

(b) capturing a first image of the target subject having the light spots in response to the projecting step;

(c) electronically calculating a triangulation measure of distance for each of a plurality of the light spots in the captured first image; and

(d) programmatically focusing the camera using a focus distance of the target subject based on the triangulation measure of distance having a lowest distance value.

18. A method according to claim 17, wherein the capturing step is carried out with QVGA resolution in viewfinder mode.

19. A method according to claim 17, wherein the programmatically focusing step is carried out using a camera to subject distance “

u”

that is calculated according to;

u=fs/np

where “

n”

represents a displacement measured in number of pixels in position between the spot in the image and a center of the image, “

f”

is a focal length of the camera lens, “

s”

is a distance between the camera lens and an emitter axis for emitter(s) used to generate the projected light spots, and “

p”

is pixel pitch.

20. A method according to claim 17, wherein the electronically calculating step comprises applying a polynomial function to pixel values representing the spot image in a direction of interest.

21. A method according to claim 17, further comprising video recording images using the cellular telephone camera while repeating steps (a)-(d), wherein the method further comprises:

electronically patching light spots in video recording images using pixel data from at least one reference viewfinder image that is devoid of light spots during video streaming to provide video recording images without light spots.