Problem with images example -- potentially local/global variables?

Programming Questions

ldiethyla..

Problem with images example -- potentially local/global variables?

in Programming Questions • 1 year ago

Hey all,

I'm trying to modify some of the image examples ( http://processing.org/learning/pixels/) to do some photo editing algorithms.

The first thing I tried was a blur algorithm:

//-----------------Globals
PImage target;
PImage destination;
float v = 1.0/9.0;
float[][] kernel = {{v,v,v},{v,v,v},{v,v,v}};
//-----------------Setup
void setup() {
size(1024,683);
target = loadImage("data/leaf.jpg");
destination = createImage(target.width, target.height, RGB);
target.loadPixels();
destination.loadPixels();
//Iterate over pixels
for (int x = 1; x < target.width - 1; x++ ) {
for (int y = 1; y < target.height - 1; y++ ) {
color blurColor = blur(kernel,3,target);
destination.pixels[y*target.width + x] = blurColor;
}
}
//Update the pixels in the destination file, show the image, and save it.
destination.updatePixels();
image(destination,0,0);
image(target,512,0);
//save("leaf_blur.png");
}
//-----------------Defined Functions
color blur(float[][] matrix, int matrixSize, PImage img) {
float redSum = 0;
float greenSum = 0;
float blueSum = 0;
for (int dx = -(matrixSize - 1) / 2; dx <= (matrixSize - 1) / 2; dx++) {
for (int dy = -(matrixSize - 1) / 2; dy <= (matrixSize - 1) / 2; dy++) {
//snag the location of the pixel
int loc = (x+dx) + (y+dy)*img.width;
// Pick a parameter of the pixel
float redVal = red(img.pixels[loc]);
float greenVal = green(img.pixels[loc]);
float blueVal = blue(img.pixels[loc]);
// Multiply adjacent pixels based on the kernel values
redSum += matrix[dy+1][dx+1]*redVal;
greenSum += matrixl[dy+1][dx+1]*greenVal;
blueSum += matrix[dy+1][dx+1]*blueVal;
return color(redSum,greenSum,blueSum);
}
}
}

but i keep getting the error 'the field Component.x is not visible', with line 39 highlighted. I thought that perhaps the image ('target') attributes weren't properly getting passed on to the blur function. However, I tried another simple example:

//-----------------Globals
PImage target;
int rad = 10;
//-----------------Setup
void setup() {
size(1024,683);
target = loadImage("data/leaf.jpg");
target.loadPixels();
int randomX = int(random(target.width));
int randomY = int(random(target.height));
int loc = x + y*target.width;
float r = red(target.pixels[loc]);
float g = green(target.pixels[loc]);
float b = blue(target.pixels[loc]);
noStroke();
fill(r,g,b,100);
ellipse(randomX,randomY,rad,rad);
//save("leaf_blur.png");

and get the EXACT same error, but this time line 14 is highlighted (coincidentally, or perhaps not, both times it is the 'int loc = ' line). There's no functions here, so it shouldn't be a problem with the function inheriting the proper attributes.

Any ideas?

Thank you SO much!

Replies(2)

PhiLho

Re: Problem with images example -- potentially local/global variables?

1 year ago

You guessed it, that's a problem of variable scope. In the first snippet, x and y are defined in the loop, and are not visible outside their respective loops. When you call a function inside the loop, the function only knows the global variables, the parameters, and the variables defined inside it. It knows nothing from the call site, unless given explicitly.
Simple cure: pass x and y as parameters to your blur function.

In the second example, you don't even define x and y...

ldiethyla..

Re: Problem with images example -- potentially local/global variables?

1 year ago

and now I feel very silly :X

The whole time I thought the problem was with img.width and couldn't figure out why....