I'm not sure I quite understand your request because I couldn't test your code properly.

Try this... it creates a tile background using an image.
It works better with a small image.
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PImage imageName;
int deltaX = 5; //space between images on the X axis
int deltaY = 5; //space between images on the Y axis

void setup() {
 size(800,800);
 background(0);
 
 imageName = loadImage("image01.gif"); //loads the image
 
 noLoop(); //only plays once
}

void draw() {
 int numberOfImages = width * height / (imageName.width + deltaX) * (imageName.height + deltaY); //counts the number of images it has to place. Total area of the sketch divided by the area of the image
 int row = 0; //initialize row

 for (int i = 0; i < numberOfImages; i++)  {
   //if i has reached it's peak value,
   if (i % int(width/imageName.width + deltaX) == 0) {
     row++;  //then add a new row
   }
   
   //position the image at the right X and Y
   image(imageName, i % int(width/imageName.width + deltaX) * (imageName.width + deltaX), (row-1) * (imageName.height+ deltaY), imageName.width, imageName.height);
 }
}
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Hope it helped!
Steven