最关键的获取亮度公式：
float luminance = (red * 0.2126f + green * 0.7152f + blue * 0.0722f) / 255;
private BufferedImage adjustBrightness(BufferedImage imgsrc) {
int width = imgsrc.getWidth();
int height = imgsrc.getHeight();
int totalPixels = width * height;
int[] intValues = new int[totalPixels];
imgsrc.getRGB(0, 0, width, height, intValues, 0, width);
int pixelLuminanceLowerThanBound = 0;
int pixelLuminanceHigherThanBound = 0;
float luminanceSum = 0.f;
for (int i = 0, j = intValues.length; i < j; i++) {
int val = intValues[i];
int red = (val >> 16) & 0xFF;
int green = ((val >> 8) & 0xFF);
int blue = val & 0xFF;
float luminance = (red * 0.2126f + green * 0.7152f + blue * 0.0722f) / 255;
if (luminance < lowerBound) {
pixelLuminanceLowerThanBound++;
}
if (luminance > upperBound) {
pixelLuminanceHigherThanBound++;
}
luminanceSum += luminance;
}
float threshold = (totalPixels * pixelAdjustmentRatio);
if (!(pixelLuminanceLowerThanBound > threshold) && !(pixelLuminanceHigherThanBound > threshold)) {
return imgsrc;
}
float luminanceMean = luminanceSum / (totalPixels);
float brightnessDiff = (float) (universalBrightness) / 100 - luminanceMean;
float expandFactor = (float) (Math.pow(1. + brightnessDiff, 2.5));
RescaleOp rescaleOp = new RescaleOp(expandFactor, 35, null);
rescaleOp.filter(imgsrc, imgsrc);
// imgsrc.setRGB(0, 0, width, height, intValues, 0, width);
return imgsrc;
}
