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Aside from the specific implementation of the pixel modification algorithm, the major difference between this sketch and the sketches since Pr0120-Image Explorer is that I have made the code more modular.
For example, I have attempted to isolate those portions of the template that are likely to change from one algorithm go the next from those portions that areless likely to change. That will make it easier to explain how the code for one algorithm differs from the code for other algorithms.
Listing 1 shows the beginning of the class and the modified run method. It is unlikely that this code will change much from one algorithm tothe next.
class Pr0140aRunner{
//The following instance variable is used to set the// color of the appropriate pixel in the output display
// window.int ctr = 0;//output pixel array countervoid run(){
background(255);//whitetextFont(font,16);//Set the font size
fill(255,0,0);//Set the text color to red//Display error message in place of image if the// image won't fit in the display window.
if(img.width>width){
text("--Image too wide--",10,20);text("Image width: " + img.width,10,40);
text("Display width: " + width,10,60);}else if(img.height>height){
text("--Image too tall--",10,20);text("Image height: " + img.height,10,40);
text("Display height: " + height,10,60);}else{
//The image will fit in the output window.//Call a method that will apply a specific// pixel-modification algorithm and write the
// modified pixel colors into the output window.processPixels();
}//end else//Display the author's name on the output in the font// size and text color defined above.
text("Dick Baldwin",10,20);//Display information about the pixel being pointed// to with the mouse. Display near the bottom of the
// output window.displayPixelInfo(img);
}//end run
The first major difference between this and previous versions of the run method is the delegation of pixel manipulation operations to the method named processPixels . Moving those operations to a separate method will decrease the likelihood that it will be necessary to modify the code in Listing 1 to implement different algorithms.
I will identify the second major change later.
The processPixels method, which begins in Listing 2 , applies a pixel modification algorithm that causes the green and blue color values to be scaled on a linearbasis moving from left to right across the image.
void processPixels(){
loadPixels();//requiredimg.loadPixels();//required
float reD,greeN,bluE;//store color values herectr = 0;//initialize output pixel array counter
The code in Listing 2 :
Listing 3 shows the beginning of a for loop that is used to process every pixel in the input pixel array.
//Process each pixel in the input image.
for(int cnt = 0;cnt<img.pixels.length;cnt++){
//Get and save RGB color values for current pixel.reD = red(img.pixels[cnt]);greeN = green(img.pixels[cnt]);bluE = blue(img.pixels[cnt]);
The code in Listing 3 gets and saves the RGB color values for the current pixel.
This algorithm applies the same scale factor to every pixel in each column. Therefore, it is necessary to identify the column to which a pixel belongs whenthe colors for the pixel are retrieved from the pixel array. However, it is not necessary to identify the row. (We will get to that in later modules.)
The code in Listing 4 uses the modulus operator to compute the column number based on the loop counter, (which is the same as the input pixel array index) .
//Compute the column number and use it to compute
// the linear scale factors that will be applied to// the green and blue color values.
int col = cnt%img.width;float greenScale = (float)(width - col)/width;
float blueScale = (float)(col)/width;
The code in Listing 4 uses the column number to compute the two required scale factors.
If case you haven't recognized it, the expression for greenScale is the equation for a straight line that goes through 1.0 on the left side ofthe image and goes through 0.0 on the right side of the image.
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