Apparatus and method of capturing images having optimized quality under night scene conditions

1. An apparatus for capturing images, comprising:

an image-capturing unit capturing an image light from an object and generating a first digital image;

a night-scene-sensing unit sensing whether the first digital image is a night-scene image;

an exposure-adjustment unit adjusting an optimized exposure time by comparing an edge level of the night-scene image with that of a pre-generated reference image if it is sensed that the input image is the night-scene image, and not adjusting an optimized exposure time if it is sensed that the input image is not the night-scene image; and

a controller controlling the image-capturing unit to generate a second digital image based on the adjusted exposure time.

2. The apparatus of claim 1 , wherein the image-capturing unit comprises:

a lens assembly adjusting the exposure time, auto focus, and aperture under the control of the controller;

an image sensor capturing the image light and generating an analog image signal; and

an analog-to-digital converter (ADC) converting the analog image signal into a digital image signal.

3. The apparatus of claim 1 , wherein the first digital image is a preview image, and the second digital image is a mega-pixel image.

4. The apparatus of claim 1 , wherein the night-scene-sensing unit senses whether the first digital image is the night-scene image on the basis of an average luminance and an exposure value of the first digital image.

5. The apparatus of claim 1 , wherein the exposure-adjustment unit comprises:

an edge-level-measurement unit measuring the edge level of the first digital image;

a first database storing first reference images captured with no blur and a permissible threshold blur level for the first reference images;

a second database storing second reference images that correspond to the first reference images and are captured with blur and a correlation between edge levels of the second reference images and exposure times; and

an exposure-time-determination unit determining the optimized exposure time from the measured edge level with reference to the first and second databases.

6. The apparatus of claim 5 , wherein the edge-level-measurement unit measures the edge level on the basis of coefficients obtained by performing a DCT of the first digital image.

7. The apparatus of claim 5 , wherein the first reference images are classified into a specified number of classes according to the edge levels of the first reference images.

8. The apparatus of claim 7 , wherein the exposure-time-determination unit searches for the second reference images that match the measured edge level and the exposure time of the first digital image, searches a class to which the first reference images corresponding to the searched second reference images belong, reads the edge level of the first reference images having the threshold blur level of the class, and determines the optimized exposure time using the correlation between the read edge level and the exposure time.

9. The apparatus of claim 5 , wherein the threshold blur level is a blur level of a visually permissible image on the basis of the first reference images among the images generated by adding an artificial blur to the first reference images for a plurality of blur levels.

10. The apparatus of claim 5 , wherein the exposure-adjustment unit further comprises a shake-compensation unit compensating for the optimized exposure time using shake information of the image-capturing unit.

11. A method of capturing images comprising:

capturing image light from an object and generating a first digital image;

sensing whether the first digital image is a night-scene image;

adjusting an optimized exposure time by comparing an edge level of the night-scene image with that of a pre-generated reference image if it is sensed that the input image is the night-scene image, and not adjusting an optimized exposure time if it is sensed that the input image is not the night-scene image; and

generating a second digital image based on the adjusted exposure time.

12. The method of claim 11 , wherein the generating of the first digital image comprises:

adjusting the exposure time, auto focus, and aperture under the control of the controller;

capturing the image light and generating an analog image signal; and

converting the analog image signal into a digital image signal.

13. The method of claim 11 , wherein the first digital image is a preview image, and the second digital image is a mega-pixel image.

14. The method of claim 11 , wherein the sensing comprises sensing whether the first digital image is the night-scene image on the basis of an average luminance and an exposure value of the first digital image.

15. The method of claim 11 , wherein the adjusting comprises:

measuring the edge level of the first digital image; and

determining the optimized exposure time from the measured edge level with reference to a first database storing first reference images captured with no blur and a permissible threshold blur level for the first reference images and a second database storing second reference images that correspond to the first reference images and are captured with blur and a correlation between edge levels of the second reference images and exposure times.

16. The method of claim 15 , wherein the measuring comprises measuring the edge level on the basis of coefficients obtained by performing a DCT of the first digital image.

17. The method of claim 15 , wherein the first reference images are classified into a specified number of classes according to the edge levels of the first reference images.

18. The method of claim 17 , wherein the determining comprises:

searching for the second reference images that match the measured edge level and the exposure time of the first digital image;

searching a class to which the first reference images corresponding to the searched second reference images belong;

reading the edge levels of the first reference images having the threshold blur level of the class; and

determining the optimized exposure time using the correlation between the read edge level and the exposure time.

19. The method of claim 15 , wherein the threshold blur level is a blur level of a visually permissible image on the basis of the first reference images among the images generated by adding an artificial blur to the first reference images for a plurality of blur levels.

20. The method of claim 15 , wherein the determining further comprises compensating for the optimized exposure time using shake information of the image.