Manipulate pixels from Capture image

Core Library Questions

drgonzo44

Manipulate pixels from Capture image

in Core Library Questions • 1 month ago

How do you read, change, and redraw pixel data from a Capture?

I'm trying to use this code: http://www.learningprocessing.com/examples/chapter-15/example-15-15/, but am getting a nullPointerException when calling "captureReference".pixels[loc]).

Any help is appreciated.

Replies(4)

jaeger83

Re: Manipulate pixels from Capture image

1 month ago

If you are getting a nullPointerException, then maybe check that everything is actually initialised, like Capture, PImage and any arrays.

If you are using a webcam and Capture you might need to check that the camera feed is actually available before looping through it's pixels.

Using the below example, perhaps put your code which loops through the capture pixels inside the block that checks the camera is available.

http://www.processing.org/reference/libraries/video/Capture.html

Hope that helps, otherwise please post some code.

drgonzo44

Re: Manipulate pixels from Capture image

1 month ago

@jaeger83, I should've mentioned the camera part was fine, as I was following the example from the page you posted. My question is how to read the pixel data from the camera. Here's the code for the whole sketch:

import processing.video.*;
Capture cam;
PImage img;
int cellsize = 4; // Dimensions of each cell in the grid
int cols, rows; // Number of columns and rows in our system
void setup()
{
size(640, 360, P3D);
cols = width/cellsize;
rows = height/cellsize;
img = createImage(width, height, RGB);
String[] cameras = Capture.list();
if (cameras.length == 0){
println("no cameras available");
exit();
} else {
println("cameras available:");
for (int i = 0; i<cameras.length; i++){
println(cameras[i]);
}
cam = new Capture(this, cameras[3]);
cam.start();
}
}
void draw()
{
if (cam.available() == true){
img.copy(cam, 0, 0, cam.width, cam.height, 0, 0, cam.width, cam.height);
img.updatePixels();
cam.read();
}
loadPixels();
cam.loadPixels();
img.loadPixels();
for ( int i = 0; i < cols;i++) {
// Begin loop for rows
for ( int j = 0; j < rows;j++) {
int x = i*cellsize + cellsize/2; // x position
int y = j*cellsize + cellsize/2; // y position
int loc = x + y*width; // Pixel array location
color c = img.pixels[loc]; // Grab the color
// Calculate a z position as a function of mouseX and pixel brightness
float z = (mouseX/(float)width) * brightness(img.pixels[loc]) - 100.0;
//float z = random(1, 100);
// Translate to the location, set fill and stroke, and draw the rect
pushMatrix();
translate(x,y,z);
fill(c);
noStroke();
rectMode(CENTER);
rect(0,0,cellsize,cellsize);
popMatrix();
}
}
}

jaeger83

Re: Manipulate pixels from Capture image

1 month ago

works for me ok, no errors!

drgonzo44

Re: Manipulate pixels from Capture image

1 month ago

The correct answer (I've since found) is to use the get() method. To get the pixel data for a frame of video, you assign a PImage instance to captureReference.get(), which returns an image. To get specific pixels, you can do captureReference.get(x,y).

Check out this dude's stuff for reference. It uses an older version of Processing, but it's still applicable.

http://www.creativecoding.org/lesson/topics/video/video-in-processing

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