I tried a bit, maybe it helps.
It aint perfect cause it should have somekind of curve in it, right now values will get out of the reach of 255 and if they do they will be set to 255 and I think that aint the best way.

The thing does work better to get a image in a certain tint, for example:
   img.pixels[i] = color(50, S, B);

will give the image a green look.

Code:

PImage img;
int H, S, B;
float B2;

void setup(){
  size(300, 300);
  img = loadImage("b.png");
  colorMode(HSB);
  noLoop();
}

void draw(){
  image(img, 0, 0);
  img.loadPixels();
  for (int i =0; i < img.pixels.length; i++){
    H = int(hue(img.pixels[i]));
    S = int(saturation(img.pixels[i]));
    B = int(brightness(img.pixels[i]));
    B2 = float(B)*2.5;
    if (B2 > 255.0){
	B2 = 255.0;
    }
    println(B2);
    
   // println(H+" "+S+" "+B);
    img.pixels[i] = color(H, S, B2);
    
  }
  img.updatePixels();

  image(img, img.width, 0);
}