How to get color saturation or brightness from YUV420SP format in Eclipse

Question

I have to make a simple app that will messure the saturation, brightness etc. from camera preview on Android. My code is now sending image to data in:

public void onPreviewFrame(byte[] data, Camera camera){

}

...and if I'm not wrong it is in YUV420SP format. I have tried to find some information about this but unsuccessful. Can anyone tell me how to manage this format?

Answer 1

See Android document: http://developer.android.com/reference/android/hardware/Camera.Parameters.html#setPreviewFormat(int); the image format is described here: http://www.fourcc.org/yuv.php#NV21.

In the nutshell, this byte[] contains two parts: luma and chroma. You can use the camera object to find the current parameters (don't use this in production code in every call to onPreviewFrame(), because these calls are performance burden, but reuse the values):

int w = camera.getParameters().getPreviewSize().width;
int h = camera.getParameters().getPreviewSize().height;

byte[] luma = new byte[w*h];
byte[] chroma = new byte[w*h/2];
System.arraycopy(data, 0, luma, 0, w*h);
System.arraycopy(data, w*h, chroma, 0, w*h/2);

int Y_at_x_y = luma[x + y*w];           // or data[x + y*w]
int U_at_x_y = chroma[x/2 + y*w/2 + 1]; // or data[w*h + x/2 + y*w/2 + 1]
int V_at_x_y = chroma[x/2 + y*w/2];     // or data[w*h + x/2 + y*w/2]