Exposure control method applicable to exposure fusion

1 . An exposure control method, the method comprising:

long-exposure adjustment steps including:

calculating a number of pixels of each brightness value of N brightness values of a long-exposure image to obtain N long-exposure-pixel statistic numbers, wherein the N long-exposure-pixel statistic numbers are corresponding to the N brightness values respectively, any two of the N brightness values are different, and the N is an integer equal to or greater than five;

adding up X long-exposure-pixel statistic number(s) of the N long-exposure-pixel statistic numbers to obtain a long-exposure bright-area total pixel number, wherein the X long-exposure-pixel statistic number(s) is/are respectively corresponding to X brightness value(s) of the N brightness values from a highest brightness value of the N brightness values to an X th highest brightness value of the N brightness values, and the X is a positive integer smaller than the N;

calculating a long-exposure brightness mean value of dark pixels of the long-exposure image, wherein all kind(s) of brightness values of the dark pixels is/are (N−X) brightness value(s) of the N brightness values from a lowest brightness value of the N brightness values to an (N−X) th lowest brightness value of the N brightness values; and

when a long-exposure brightness-mean-value difference between the long-exposure brightness mean value and a long-exposure target brightness mean value is greater than a predetermined long-exposure brightness-mean-value difference, adjusting long-exposure setting that is used for generating the long-exposure image and then making the long-exposure setting be applied to generation/modification of the long-exposure image to prevent the long-exposure brightness-mean-value difference from being greater than the predetermined long-exposure brightness-mean-value difference; and

short-exposure adjustment steps including:

determining a number of pixels of each brightness value of plural brightness values of the N brightness values of a short-exposure image to obtain plural short-exposure-pixel statistic numbers, wherein the plural short-exposure-pixel statistic numbers are corresponding to the plural brightness values respectively, the short-exposure image and the long-exposure image are two images of a same scene and have same sizes, and an exposure amount of the long-exposure setting is more than an exposure amount of short-exposure setting that is used for generating the short-exposure image;

determining K pixels of the short-exposure image from pixel(s) of the highest brightness value in top-down brightness order, wherein the K is a short-exposure bright-area total pixel number, and a number difference between the short-exposure bright-area total pixel number and the long-exposure bright-area total pixel number is not greater than a predetermined number difference;

calculating a short-exposure brightness mean value of the K pixels; and

when a short-exposure brightness-mean-value difference between the short-exposure brightness mean value and a short-exposure target brightness mean value is greater than a predetermined short-exposure brightness-mean-value difference, adjusting the short-exposure setting and then making the short-exposure setting be applied to generation/modification of the short-exposure image to prevent the short-exposure brightness-mean-value difference from being greater than the predetermined short-exposure brightness-mean-value difference.

2 . The method of claim 1 , wherein the short-exposure bright-area total pixel number is set to be equal to the long-exposure bright-area total pixel number.

3 . The method of claim 1 , wherein a sum of the N long-exposure-pixel statistic numbers is a long-exposure total pixel number, and the long-exposure adjustment steps further include:

dividing the long-exposure bright-area total pixel number by the long-exposure total pixel number to obtain a bright-area ratio; and

when the bright-area ratio is greater than a predetermined bright-area ratio, decreasing the exposure amount of the long-exposure setting.

4 . The method of claim 3 , wherein the long-exposure adjustment steps further include: before calculating the long-exposure brightness mean value, making the bright-area ratio be equal to or smaller than the predetermined bright-area ratio.

5 . The method of claim 1 , wherein a sum of the N long-exposure-pixel statistic numbers is a long-exposure total pixel number, and the long-exposure adjustment steps further include:

adding up Y long-exposure-pixel statistic number(s) of the N long-exposure-pixel statistic numbers to obtain a long-exposure dark-area total pixel number, wherein the Y long-exposure-pixel statistic number(s) is/are respectively corresponding to Y brightness value(s) of the N brightness values from the lowest brightness value of the N brightness values to a Y th lowest brightness value of the N brightness values, and the Y is a positive integer smaller than the N;

dividing the long-exposure dark-area total pixel number by the long-exposure total pixel number to obtain a dark-area ratio; and

when the dark-area ratio is greater than a predetermined dark-area ratio, increasing the exposure amount of the long-exposure setting.

6 . The method of claim 5 , wherein the long-exposure adjustment steps further include: before calculating the long-exposure brightness mean value, making the dark-area ratio be equal to or smaller than the predetermined dark-area ratio.

7 . The method of claim 1 , wherein the (N−X) brightness value(s) is/are corresponding to (N−X) long-exposure-pixel statistic number(s) of the N long-exposure-pixel statistic numbers respectively, and the step of calculating the long-exposure brightness mean value includes:

multiplying the (N−X) brightness value(s) by the (N−X) long-exposure-pixel statistic number(s) respectively and then adding up all products to obtain a total product; and then dividing the total product by a sum of the (N−X) long-exposure-pixel statistic number(s) to obtain the long-exposure brightness mean value.

8 . The method of claim 1 , wherein the long-exposure adjustment steps further include: when the exposure amount of the long-exposure setting is adjusted, adjusting the exposure amount of the short-exposure setting correspondingly.

9 . The method of claim 8 , wherein the long-exposure adjustment steps further include:

the exposure amount of the long-exposure setting is adjusted by a long-exposure adjustment amount, and the exposure amount of the short-exposure setting is adjusted by a short-exposure adjustment amount; and

a ratio of the long-exposure adjustment amount to the short-exposure adjustment amount complies with a predetermined ratio, or an adjustment difference between the long-exposure adjustment amount and the short-exposure adjustment amount is less than a predetermined adjustment difference.

10 . The method of claim 1 , wherein all kinds of brightness values of the K pixels are M brightness values of the N brightness values from the highest brightness value of the N brightness values to an M th highest brightness value of the N brightness values, (M−1) brightness value(s) of the M brightness values from the highest brightness value of the N brightness values to an (M−1) th brightness value of the N brightness values is/are corresponding to (M−1) short-exposure-pixel statistic number(s) of the plural short-exposure-pixel statistic numbers respectively, a lowest brightness value of the M brightness values is corresponding to a calculation statistic number which is equal to a result of subtracting a sum of the (M−1) short-exposure-pixel statistic numbers from the K, the M is an integer greater than one and smaller than the N, and the step of calculating the short-exposure brightness mean value includes:

multiplying the (M−1) brightness values by the (M−1) short-exposure-pixel statistic numbers respectively and then adding up all products to obtain a first product; multiplying the lowest brightness value of the M brightness values by the calculation statistic number to obtain a second product; and dividing a sum of the first product and the second product by the K to obtain the short-exposure brightness mean value.

11 . An exposure control method, the method comprising:

long-exposure adjustment steps including:

calculating a long-exposure brightness mean value of dark pixels of a long-exposure image, wherein all kind(s) of brightness values of the dark pixels is/are (N−X) brightness value(s) of N brightness values of the long-exposure image from a lowest brightness value of the N brightness values to an (N−X) th lowest brightness value of the N brightness values, wherein a total number of bright pixels of the long-exposure image is a long-exposure bright-area total pixel number, all kind(s) of brightness values of the bright pixels is/are X brightness value(s) of the N brightness values from a highest brightness value of the N brightness values to an X th highest brightness value of the N brightness values, any two of the N brightness values are different, the N is an integer equal to or greater than five, and the X is a positive integer smaller than the N; and

when a long-exposure brightness-mean-value difference between the long-exposure brightness mean value and a long-exposure target brightness mean value is greater than a predetermined long-exposure brightness-mean-value difference, adjusting long-exposure setting that is used for generating the long-exposure image and then making the long-exposure setting be applied to generation/modification of the long-exposure image to prevent the long-exposure brightness-mean-value difference from being greater than the predetermined long-exposure brightness-mean-value difference; and

short-exposure adjustment steps including:

determining K pixels of a short-exposure image from pixel(s) of the highest brightness value in top-down brightness order, wherein the short-exposure image and the long-exposure image are two images of a same scene and have same sizes, and an exposure amount of the long-exposure setting is more than an exposure amount of short-exposure setting that is used for generating the short-exposure image, the K is a short-exposure bright-area total pixel number, and a number difference between the short-exposure bright-area total pixel number and the long-exposure bright-area total pixel number is not greater than a predetermined number difference;

calculating a short-exposure brightness mean value of the K pixels; and

when a short-exposure brightness-mean-value difference between the short-exposure brightness mean value and a short-exposure target brightness mean value is greater than a predetermined short-exposure brightness-mean-value difference, adjusting the short-exposure setting and then making the short-exposure setting be applied to generation/modification of the short-exposure image to prevent the short-exposure brightness-mean-value difference from being greater than the predetermined short-exposure brightness-mean-value difference.

12 . The method of claim 11 , wherein the long-exposure adjustment steps further include:

when the exposure amount of the long-exposure setting is adjusted by a long-exposure adjustment amount, adjusting the exposure amount of the short-exposure setting by a short-exposure adjustment amount correspondingly,

wherein a ratio of the long-exposure adjustment amount to the short-exposure adjustment amount complies with a predetermined ratio, or an adjustment difference between the long-exposure adjustment amount and the short-exposure adjustment amount is less than a predetermined adjustment difference.