this works for colour images as well and show how to iterate through the pixel values. you can modify this example to adjust hue or saturation if you want. please make sure you place an test.jpg image inside your data folder so this works.
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- PImage img;
- PImage imgEnhanced;
- void setup()
- {
- //make this big enough so you can see all of your image
- size(200, 200);
-
- //things we only do once in the program should be here
- //put a test.jpg image in a folder called data inside the sketch folder
- img = loadImage("test.jpg");
- imgEnhanced = new PImage(img.width, img.height);
- }
- void draw()
- {
- background(0);
-
- //just use the mouse positions to work out
- //contrast and brightness values
- //up down is brightness
- //left right is contrast
-
- //contrast - this probably doesn't need to be bigger than 5 or 10
- float contrast = 5f * ( mouseX / (float)width); //value should go from 0 to 5
- println("contrast: " + contrast);
-
- //brightness - this is additive and we want to make it both brigher and darker so -128 to +128
- float bright = 255 * ( mouseY / (float)width - 0.5); //value should go from -128 to +128
- println("contrast: " + contrast);
-
- //call out contrast and brightness function
- ContrastAndBrightness(img,imgEnhanced, contrast,bright);
-
- //display the image
- image(imgEnhanced, 0,0);
- }
- //image processing function to enhance contrast
- //this doesn't make sense without also adjusting the brightness at the same time
- void ContrastAndBrightness(PImage input, PImage output,float cont,float bright)
- {
- int w = input.width;
- int h = input.height;
-
- //our assumption is the image sizes are the same
- //so test this here and if it's not true just return with a warning
- if(w != output.width || h != output.height)
- {
- println("error: image dimensions must agree");
- return;
- }
-
- //this is required before manipulating the image pixels directly
- input.loadPixels();
- output.loadPixels();
-
- //loop through all pixels in the image
- for(int i = 0; i < w*h; i++)
- {
- //get color values from the current pixel (which are stored as a list of type 'color')
- color inColor = input.pixels[i];
-
- //slow version for illustration purposes - calling a function inside this loop
- //is a big no no, it will be very slow, plust we need an extra cast
- //as this loop is being called w * h times, that can be a million times or more!
- //so comment this version and use the one below
- int r = (int) red(input.pixels[i]);
- int g = (int) green(input.pixels[i]);
- int b = (int) blue(input.pixels[i]);
-
- //here the much faster version (uses bit-shifting) - uncomment to try
- //int r = (inColor >> 16) & 0xFF; //like calling the function red(), but faster
- //int g = (inColor >> 8) & 0xFF;
- //int b = inColor & 0xFF;
-
- //apply contrast (multiplcation) and brightness (addition)
- r = (int)(r * cont + bright); //floating point aritmetic so convert back to int with a cast (i.e. '(int)');
- g = (int)(g * cont + bright);
- b = (int)(b * cont + bright);
-
- //slow but absolutely essential - check that we don't overflow (i.e. r,g and b must be in the range of 0 to 255)
- //to explain: this nest two statements, sperately it would be r = r < 0 ? 0 : r; and r = r > 255 ? 255 : 0;
- //you can also do this with if statements and it would do the same just take up more space
- r = r < 0 ? 0 : r > 255 ? 255 : r;
- g = g < 0 ? 0 : g > 255 ? 255 : g;
- b = b < 0 ? 0 : b > 255 ? 255 : b;
-
- //and again in reverse for illustration - calling the color function is slow so use the bit-shifting version below
- output.pixels[i] = color(r ,g,b);
- //output.pixels[i]= 0xff000000 | (r << 16) | (g << 8) | b; //this does the same but faster
-
- }
-
- //so that we can display the new image we must call this for each image
- input.updatePixels();
- output.updatePixels();
- }
