Exposure control method applicable to exposure fusion

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 Xth 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.