Method of adjusting bitrate of image and image capturing apparatus, and method of generating bitrate-adjusted image

1. A method of adjusting an output bitrate of an image by contrast adjustment, the method comprising:

determining a maximum subtraction rate of a contrast of the image in response to a brightness of the image;

comparing a current output bitrate of the image with a target bitrate while reducing the contrast of the image up to the determined maximum subtraction rate of the contrast of the image; and

determining the contrast of the image to be the reduced contrast in response to determining that the reduced contrast of the image corresponds to the target bitrate.

2. The method of claim 1 , wherein the determining of the maximum subtraction rate comprises:

calculating an average value of the brightness of the image and a degree of variance of the brightness; and

determining the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness.

3. The method of claim 2 , wherein the determining of the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness comprises:

reducing the maximum subtraction rate of the contrast of the image as the average value of the brightness increases.

4. The method of claim 2 , wherein the determining of the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness comprises:

reducing the maximum subtraction rate of the contrast of the image as the degree of variance of the brightness increases.

5. The method of claim 2 , wherein the determining of the maximum subtraction rate of the contrast of the image comprises: determining the maximum subtraction rate to be:

a first subtraction rate in response to determining that the average value of the brightness is equal to or greater than a predetermined threshold average value and the degree of variance of the brightness is equal to or greater than a predetermined threshold degree of variance;

a second subtraction rate in response to determining that the average value of the brightness is equal to or greater than a predetermined threshold average value and the degree of variance of the brightness is less than a predetermined threshold degree of variance;

a third subtraction rate in response to determining that the average value of the brightness is less than a predetermined threshold average value and the degree of variance of the brightness is equal to or greater than a predetermined threshold degree of variance; and

a fourth subtraction rate in response to determining that the average value of the brightness is less than a predetermined threshold average value and the degree of variance of the brightness is less than a predetermined threshold degree of variance,

wherein the fourth subtraction rate is equal to or greater than the third subtraction rate,

wherein the third subtraction rate is equal to or greater than the second subtraction rate, and

wherein the second subtraction rate is equal to or greater than the first subtraction rate.

6. The method of claim 2 , wherein the image comprises a plurality of frames, and

wherein the calculating of the average value of the brightness of the image and the degree of variance of the brightness comprises calculating an average value of a brightness of each of at least one of the plurality of frames and a degree of variance of the brightness of each of at least one of the plurality of frames,

wherein the determining of the maximum subtraction rate of the contrast of the image in response to the average value of the brightness of each of at least one of the plurality of frames and the degree of variance of the brightness of each of at least one of the plurality of frames comprises determining a maximum subtraction rate of a contrast of each of the at least one of the plurality of frames based on an average value of the brightness of each of at least one of the plurality of frames calculated with respect to each of the at least one of the plurality of frames and the degree of variance of the brightness of each of at least one of the plurality of frames,

wherein the comparing of the current output bitrate of the image comprises comparing a current output bitrate with the target bitrate while reducing the contrast up to the maximum subtraction rate of the contrast determined with respect to each of the at least one of the plurality of frames,

the determining of the reduced contrast comprises determining the contrast of the image to be the reduced contrast of the image in response to determining that the reduced contrast of the each of the at least one of the plurality of frames corresponds to the target bitrate.

7. The method of claim 1 , wherein, the determining of the contrast comprises, in response to determining that the output bitrate and the target bitrate do not correspond to each other while reducing the contrast to correspond to the maximum subtraction rate, determining the contrast reduced by the corresponding maximum subtraction rate as a contrast of the image,

wherein the method further comprises, after determining of the contrast,

comparing a current output bitrate of the image with the target bitrate while increasing a quantization parameter of the image; and

determining the quantization parameter of the image to be the increased quantization parameter in response to determining that the increased quantization parameter corresponds to the target bitrate.

8. The method of claim 7 , further comprising, after the determining the quantization parameter, applying the determined contrast of the image to the image and encoding the image, to which the contrast is applied, based on the determined quantization parameter of the image.

9. The method of claim 1 , wherein the comparing of the current output bitrate comprises comparing the current output bitrate of the image with the target bitrate while reducing the contrast of the image from a current contrast of the image to a contrast corresponding to the maximum subtraction rate.

10. The method of claim 1 , wherein the comparing of the current output bitrate comprises comparing the current output bitrate of the image with the target bitrate while reducing the contrast of the image from a contrast that is in a predetermined relationship with a contrast corresponding to the maximum subtraction rate, to the contrast corresponding to the maximum subtraction rate.

11. An image capturing apparatus for adjusting an output bitrate of an image based on contrast adjustment, the image capturing apparatus comprising a controller, the controller being configured to:

determine a maximum subtraction rate of a contrast of the image in response to a brightness of the image;

compare a current output bitrate of the image with a target bitrate while reducing the contrast of the image up to the determined maximum subtraction rate of the contrast of the image; and

determine the contrast of the image to be the reduced contrast in response to determining that the reduced contrast of the image corresponds to the target bitrate.

12. The image capturing apparatus of claim 11 , wherein the controller is further configured to:

calculate an average value of the brightness of the image and a degree of variance of the brightness; and

determine the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness.

13. The image capturing apparatus of claim 12 , wherein the controller is further configured to:

reduce the maximum subtraction rate of the contrast of the image as the average value of the brightness increases; and

reduce the maximum subtraction rate of the contrast of the image as the degree of variance of the brightness increases.

14. The image capturing apparatus of claim 12 , wherein the maximum subtraction rate is determined, by the controller, to be:

a first subtraction rate in response to determining that the average value of the brightness is equal to or greater than a predetermined threshold average value and the degree of variance of the brightness is equal to or greater than a predetermined threshold degree of variance;

a second subtraction rate in response to determining that the average value of the brightness is equal to or greater than a predetermined threshold average value and the degree of variance of the brightness is less than a predetermined threshold degree of variance;

a third subtraction rate in response to determining that the average value of the brightness is less than a predetermined threshold average value and the degree of variance of the brightness is equal to or greater than a predetermined threshold degree of variance; and

a fourth subtraction rate in response to determining that the average value of the brightness is less than a predetermined threshold average value and the degree of variance of the brightness is less than a predetermined threshold degree of variance,

wherein the fourth subtraction rate is equal to or greater than the third subtraction rate,

wherein the third subtraction rate is equal to or greater than the second subtraction rate, and

wherein the second subtraction rate is equal to or greater than the first subtraction rate.

15. The image capturing apparatus of claim 12 , wherein the

image comprises a plurality of frames, and

wherein the controller is further configured to

calculate an average value of a brightness of each of at least one of the plurality of frames from among the plurality of frames and a degree of variance of the brightness of each of at least one of the plurality of frames;

determine a maximum subtraction rate of a contrast of each of the at least one of the plurality of frames based on an average value of the brightness of each of at least one of the plurality of frames calculated with respect to each of the at least one of the plurality of frames and the degree of variance of the brightness of each of at least one of the plurality of frames;

compare a current output bitrate with the target bitrate while reducing the contrast at up to the maximum subtraction rate of the contrast determined with respect to each of the at least one of the plurality of frames; and

determine the contrast of the image to be the reduced contrast of the image in response to determining that the reduced contrast of the each of the at least one of the plurality of frames corresponds to the target bitrate.

16. The image capturing apparatus of claim 11 , wherein, in response to determining that the output bitrate and the target bitrate do not correspond to each other while reducing the contrast to correspond to the maximum subtraction rate, the controller configured to:

determine the contrast reduced by the corresponding maximum subtraction rate as a contrast of the image;

compare a current output bitrate of the image with the target bitrate while increasing a quantization parameter of the image; and

determine the quantization parameter of the image to be the increased quantization parameter in response to determining that the increased quantization parameter corresponds to the target bitrate.

17. A method of generating an image by adjusting a bitrate of the image based on contrast adjustment, the method comprising:

determining a maximum subtraction rate of a contrast of the image in response to a brightness of the image;

reducing a contrast of the image such that the contrast of the image corresponds to the maximum subtraction rate of the contrast of the image; and

encoding the image according to the adjusted contrast,

wherein the determining of the maximum subtraction rate comprises:

calculating an average value of the brightness of the image and a degree of variance of the brightness; and

determining the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness, and

wherein the determining of the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness comprises:

reducing the maximum subtraction rate of the contrast of the image as the average value of the brightness increases.

18. The method of claim 17 , wherein the determining of the maximum subtraction rate of the contrast of the image in response to the average value of the brightness and the degree of variance of the brightness comprises:

reducing the maximum subtraction rate of the contrast of the image as the degree of variance of the brightness increases.