Android Adventures, part 5: access the camera in Processing
This became far more difficult than anything previous I’d tried to do with the hardware 
I thought it would be a simple matter to access the camera’s pixel data in Processing, but that was not the case. And I should point out I can’t take credit for everything below: The camera passes back a byte stream encoded in YUV format, that my brain simply couldn’t\wouldn’t decode. I’d already ran across the Ketai library before (here, & here), and discovered that they had written a YUV decoder function (since they’ve already completed this exercise I’m trying…), so my solution below uses a direct implementation of their code. So a huge thank you to that project!
As well, I used concepts for my CameraSurfaceView class from examples in the book Android Wireless Application Development, page 340.
At any rate, it works. Camera pixel data is passed to Processing, and displayed as a PImage on the screen. It’s not fast (1 fps?), which is a bit disappointing, but it’s a start!
/**
CameraPixelData
Eric Pavey - 2010-11-15
Set Sketch Permissions : CAMERA
Add to AndroidManifest.xml:
uses-feature android:name="android.hardware.camera"
uses-feature android:name="android.hardware.camera.autofocus"
*/
import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.Surface;
// Setup camera globals:
CameraSurfaceView gCamSurfView;
// This is the physical image drawn on the screen representing the camera:
PImage gBuffer;
void setup() {
size(screenWidth, screenHeight, A2D);
}
void draw() {
// nuttin'... onPreviewFrame below handles all the drawing.
}
//-----------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------
// Override the parent (super) Activity class:
// States onCreate(), onStart(), and onStop() aren't called by the sketch. Processing is entered
// at the 'onResume()' state, and exits at the 'onPause()' state, so just override them:
void onResume() {
super.onResume();
println("onResume()!");
// Sete orientation here, before Processing really starts, or it can get angry:
orientation(LANDSCAPE);
// Create our 'CameraSurfaceView' objects, that works the magic:
gCamSurfView = new CameraSurfaceView(this.getApplicationContext());
}
//-----------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------
class CameraSurfaceView extends SurfaceView implements SurfaceHolder.Callback, Camera.PreviewCallback {
// Object that accesses the camera, and updates our image data
// Using ideas pulled from 'Android Wireless Application Development', page 340
SurfaceHolder mHolder;
Camera cam = null;
Camera.Size prevSize;
// SurfaceView Constructor: : ---------------------------------------------------
CameraSurfaceView(Context context) {
super(context);
// Processing PApplets come with their own SurfaceView object which can be accessed
// directly via its object name, 'surfaceView', or via the below function:
// mHolder = surfaceView.getHolder();
mHolder = getSurfaceHolder();
// Add this object as a callback:
mHolder.addCallback(this);
}
// SurfaceHolder.Callback stuff: ------------------------------------------------------
void surfaceCreated (SurfaceHolder holder) {
// When the SurfaceHolder is created, create our camera, and register our
// camera's preview callback, which will fire on each frame of preview:
cam = Camera.open();
cam.setPreviewCallback(this);
Camera.Parameters parameters = cam.getParameters();
// Find our preview size, and init our global PImage:
prevSize = parameters.getPreviewSize();
gBuffer = createImage(prevSize.width, prevSize.height, RGB);
}
void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// Start our camera previewing:
cam.startPreview();
}
void surfaceDestroyed (SurfaceHolder holder) {
// Give the cam back to the phone:
cam.stopPreview();
cam.release();
cam = null;
}
// Camera.PreviewCallback stuff: ------------------------------------------------------
void onPreviewFrame(byte[] data, Camera cam) {
// This is called every frame of the preview. Update our global PImage.
gBuffer.loadPixels();
// Decode our camera byte data into RGB data:
decodeYUV420SP(gBuffer.pixels, data, prevSize.width, prevSize.height);
gBuffer.updatePixels();
// Draw to screen:
image(gBuffer, 0, 0);
}
// Byte decoder : ---------------------------------------------------------------------
void decodeYUV420SP(int[] rgb, byte[] yuv420sp, int width, int height) {
// Pulled directly from:
// http://ketai.googlecode.com/svn/trunk/ketai/src/edu/uic/ketai/inputService/KetaiCamera.java
final int frameSize = width * height;
for (int j = 0, yp = 0; j < height; j++) { int uvp = frameSize + (j >> 1) * width, u = 0, v = 0;
for (int i = 0; i < width; i++, yp++) {
int y = (0xff & ((int) yuv420sp[yp])) - 16;
if (y < 0)
y = 0;
if ((i & 1) == 0) {
v = (0xff & yuv420sp[uvp++]) - 128;
u = (0xff & yuv420sp[uvp++]) - 128;
}
int y1192 = 1192 * y;
int r = (y1192 + 1634 * v);
int g = (y1192 - 833 * v - 400 * u);
int b = (y1192 + 2066 * u);
if (r < 0)
r = 0;
else if (r > 262143)
r = 262143;
if (g < 0)
g = 0;
else if (g > 262143)
g = 262143;
if (b < 0)
b = 0;
else if (b > 262143)
b = 262143;
rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) & 0xff00) | ((b >> 10) & 0xff);
}
}
}
}
Based on the success of my previous post covering how I got my Android phone (Samsung Captivate) rooted, the “
Hot off the heels of my