Affects the original image for some reason. Can somebody take a look at this?

1. PImage rocks;
   PImage rocksBrightened;
   int rockBytes[][];
   int rockBrights[][];
   void setup() {
     rocks = loadImage("rocks.jpg");
     rocksBrightened = loadImage("notrocks.jpg");
     rocks.loadPixels();
     int h = rocks.height;
     size(rocks.width*2, rocks.height*2);
     image(rocks, 0, 0);
     rockBytes = new int[rocks.width][rocks.height];
     rockBrights = new int[rocks.width][rocks.height];
     for (int i = 0; i < rocks.width; i++) {
       for (int j = 0; j < rocks.height; j++) {
         rockBytes[i][j] = rocks.get(i, j);
       }
     }
      for (int i = 0; i < rocks.width; i++) {
       for (int j = 0; j < rocks.height; j++) {
         rockBrights[i][j] = rocksBrightened.get(i, j);
       }
     }
     drawHistogram(rocks, computeHistogram (rocks));
     brighten(rockBrights);
     makeImage(rocksBrightened, rockBrights);
     image(rocksBrightened, 0, h);
   }
   void loadPixelArray(PImage anImage) {
     anImage.loadPixels(); //load pixels into pixels[] array
   }
   int[] computeHistogram (PImage anImage) {
     int histogram[] = new int[256];
     loadPixelArray(anImage);
     int histMax = 0;
     for (int x = 0; x < anImage.width; x++) {
       for (int y = 0; y < anImage.height; y++ ) {
         // Calculate the 1D pixel location
         int loc = x + y*anImage.width;
         histogram[int(red(anImage.pixels[loc]))]++;
       }
     }
     for (int i = 0; i < histogram.length; i++) {
       if (histogram[i] > histMax) {
         histMax = histogram[i];
       }
     }
     for (int i = 0; i < histogram.length; i++) {
       histogram[i] = histogram[i]*100/histMax;
     }
     return histogram;
   }
   
   void brighten(int anyArray[][]) {
     for (int i = 0; i < anyArray.length; i++){
       for (int j = 0; j < anyArray[0].length; j++) {
         anyArray[i][j] = int(-0.004436*anyArray[i][j]) + int(2.1308*anyArray[i][j]);    
       }
     }
     }
   
   void drawHistogram(PImage anImage, int histogram[]) {
     noStroke();
     fill(0);
     rect(anImage.width+1, 0, anImage.width, anImage.height);
     for (int i = 0; i < 256; i++) {
       stroke(255);
       line(anImage.width + i, anImage.height, anImage.width + i, anImage.height - histogram[i]);
     }
   }
   
   void makeImage(PImage anImage, int imgArray[][]) {
     anImage.loadPixels();
     for (int i = 0; i < imgArray.length; i++) {
       for (int j = 0; j < imgArray[0].length; j++) {
         int loc = i + j*imgArray.length;
         set(i, j, color(imgArray[i][j]));
       }
     }
     anImage.updatePixels();
   }
   

1. PImage rocks;
2. int rockBytes[][];
3. int histogram[];
4. void setup() {
5.       rocks = loadImage("rocks.jpg");
6.       rocks.loadPixels();
   
7.       histogram = new int[256];
   
8.       size(rocks.width*2, rocks.height*2);
   
9.       image(rocks, 0, 0);
   
10.       rockBytes = new int[rocks.width][rocks.height];
    
11.       for (int i = 0; i < rocks.width; i++) {
    
12.             for (int j = 0; j < rocks.height; j++) {
                      rockBytes[i][j] = rocks.get(i, j);
    
13.             }
    
14.       }
    
15.       computeHistogram (rocks);
    
16. }
    
17. void loadPixelArray(PImage anImage){
    
18.       anImage.loadPixels(); //load pixels into pixels[] array
19. }
    
20. void computeHistogram(PImage anImage) {
    
21.       loadPixelArray(anImage);
    
22.       int histMax = 0;
    
23.       for (int x = 0; x < anImage.width; x++) {
    
24.             for (int y = 0; y < anImage.height; y++ ) {
    
25.                   int loc = x + y*anImage.width;
    
26.                   histogram[anImage.pixels[loc]]++;
    
27.             }
28.   }
    
29.       for (int i = 0; i < histogram.length; i++) {            
30.       if (histogram[i] > histMax) {
    
31.             histMax = histogram[i];
    
32.             }
    
33. }
    
34.       for (int i = 0; i < histogram.length; i++) {
    
35.             histogram[i] = histogram[i]*100/histMax;
    
36. }
    
37. }

1. 
   

1. PImage rocks = loadImage("rocks.jpg");
   rocks.loadPixels();
   
   void setup() {
         size(rocks.width*2, rocks.height*2);
         image(rocks, 0, 0);
   }

I have an assignment for school that involves displaying a base colour and then a darker version of that colour. Do I actually have to get the RGB values of the base colour and alter them individually to prevent the value wrapping around when it hits 0, or is there a quick and dirty way to do this? (This is my first programming class ever so speak slowly and use little words!)