# How to apply color pixels

Hi all, I’m new using processing and still learning, I hope someone can help me .

I have this script of the reaction Diffusion, I just want to apply a color of the chemical A and B.
Also how to import an image and apply the reaction diffusion of that image that I imported,

Hope someone can help, below the script for processing 3, :

``````Cell[][] grid;
Cell[][] prev;

void setup() {
size(300, 300);
grid = new Cell[width][height];
prev = new Cell[width][height];

for (int i = 0; i < width; i++) {
for (int j = 0; j < height; j ++) {
float a = 1;
float b = 0;
grid[i][j] = new Cell(a, b);
prev[i][j] = new Cell(a, b);
}
}

for (int n = 0; n < 10; n++) {
int startx = int(random(20, width-20));
int starty = int(random(20, height-20));

for (int i = startx; i < startx+10; i++) {
for (int j = starty; j < starty+10; j ++) {
float a = 1;
float b = 1;
grid[i][j] = new Cell(a, b);
prev[i][j] = new Cell(a, b);
}
}
}
}

float dA = 1.0;
float dB = 0.5;
float feed = 0.055;
float k = 0.062;

class Cell {
float a;
float b;

Cell(float a_, float b_) {
a = a_;
b = b_;
}
}

void update() {
for (int i = 1; i < width-1; i++) {
for (int j = 1; j < height-1; j ++) {

Cell spot = prev[i][j];
Cell newspot = grid[i][j];

float a = spot.a;
float b = spot.b;

float laplaceA = 0;
laplaceA += a*-1;
laplaceA += prev[i+1][j].a*0.2;
laplaceA += prev[i-1][j].a*0.2;
laplaceA += prev[i][j+1].a*0.2;
laplaceA += prev[i][j-1].a*0.2;
laplaceA += prev[i-1][j-1].a*0.05;
laplaceA += prev[i+1][j-1].a*0.05;
laplaceA += prev[i-1][j+1].a*0.05;
laplaceA += prev[i+1][j+1].a*0.05;

float laplaceB = 0;
laplaceB += b*-1;
laplaceB += prev[i+1][j].b*0.2;
laplaceB += prev[i-1][j].b*0.2;
laplaceB += prev[i][j+1].b*0.2;
laplaceB += prev[i][j-1].b*0.2;
laplaceB += prev[i-1][j-1].b*0.05;
laplaceB += prev[i+1][j-1].b*0.05;
laplaceB += prev[i-1][j+1].b*0.05;
laplaceB += prev[i+1][j+1].b*0.05;

newspot.a = a + (dA*laplaceA - a*b*b + feed*(1-a))*1;
newspot.b = b + (dB*laplaceB + a*b*b - (k+feed)*b)*1;

newspot.a = constrain(newspot.a, 0, 1);
newspot.b = constrain(newspot.b, 0, 1);
}
}
}

void swap() {
Cell[][] temp = prev;
prev = grid;
grid = temp;
}

void draw() {
println(frameRate);

for (int i = 0; i < 1; i++) {
update();
swap();
}

for (int i = 1; i < width-1; i++) {
for (int j = 1; j < height-1; j ++) {
//pixels[j]= color(0,0,255);

Cell spot = grid[i][j];
float a = spot.a;
float b = spot.b;
int pos = i + j * width;

pixels[pos] = color((a-b)*255);
//pixels[pos] = color((a-b)*255,0,0);
}
}
updatePixels();
}
``````
1 Like

Hi Alice, welcome to the community!

To get a mix between two colors you can can use lerpColor(), which blends two colors together with a weighted average.

``````color aColor = color(204, 102, 0); //color of chemical a
color bColor = color(0, 102, 153); //color of chemical b
pixels[pos] = lerpColor(aColor, bColor, (a-b)); //blend of a and b's colors depending on how much a or b there is
``````

You can import an image by placing it in your sketch folder and then by using the following code:

``````PImage img; //declare the variable

void setup(){
...
...
}
``````

If you then want to display the image you can use the image function.

I’m not sure what you mean by this.
Do you mean overlaying the image
or blending between two images
or warping the pixels?
Do you have an example of what you are trying to achieve?

Also could you make sure your code is properly indented (press crtl+T in the Processing IDE) and format it as code (select the code and press the </> button here on the forum).

2 Likes

Hi Wizard, @TheWizardBear
Thanks for your quick reply and help! the colour is working perfectly !
I sent you some images to show you what I’m trying to achieve: from the lines of an image I can have different pattern or also to start from lines or dots.

Please let me know If It’s clear and thanks again

Cheers

1 Like

Ha ha I understand what you are trying to achieve now but I don’t really know how to achieve it!

Maybe try seeding the image with more of chemical a/b where the picture is lighter/darker or where there is more of a color difference between that pixel and nearby ones?
Perhaps you could try to limit the spread or have a higher kill rate where the picture is darker?

There is probably some documentation (e.g. articles or code) for this kind of effect somewhere, you just have to find it! Where did you get these images from? Maybe there is some more information there?

Hi @TheWizardBear I found those images in internet but now I’m trying to find more documentations and more tutorial of processing to see how to do It No problem. Sorry I didn’t know how do do that reaction/diffusion image thing.
If you still can’t work out how to do it, try opening it as new topic (though I would try out a few things first like increasing the kill/feed rate where the picture is lighter/darker).

@TheWizardBear Hi, I tried to set the color in this new code but It’s not working here… Also how I can “deactivate” the mouse pressed ( It means that when I draw in the window, the reaction /diffusion will formed, but I don’t want )
Below the code in proccessing 1.5,
Thanks a lot

<

import toxi.sim.grayscott.;
import toxi.math.
;

GrayScott gs;

void setup() {
size(256, 256);
gs=new GrayScott(width, height, false);
gs.setCoefficients(0.023, 0.074, 0.095, 0.03);
}

void draw() {
if (mousePressed) {
gs.setRect(mouseX, mouseY, 20, 20);
}
for (int i=0; i<10; i++) gs.update(1);
for (int i=0; i<gs.v.length; i++) {
float cellValue=gs.v[i];
int col=255-(int)(min(255, cellValue*768));

``````pixels[i]=col<<16|col<<8|col|0xff000000;
``````

}
updatePixels();
}

void keyPressed() {
gs.reset();
}

Maybe try removing this if statement:
`if (mousePressed) {`

Thanks a lot for your help, I’m still working on it ,

Cheers