Right after a long fight with Android API I have managed to get this working.
There were two issues that caused the green/purple output;
Loss of data: the generated YUV frame was larger than the original preview frame at the same resolution, so the data being passed down to the native code was missing around 30% of its image data.
Wrong resolution: the native code required the resolution of the preview frame and not the camera.
Below is a working solution for anyone who wishes to add a static frame;
so updated code:
@Override
public byte[] getPreviewFrameData(int width, int height) {
if (mPreviewFrameData == null) {
loadPreviewFrame(width, height);
}
return mPreviewFrameData;
}
private void loadPreviewFrame(int width, int height) {
try {
Bitmap previewImage = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.frame);
Bitmap resizedPreviewImage = Bitmap.createScaledBitmap(previewImage, width, height, false);
BitmapConverter bitmapConverter = new BitmapConverter();
mPreviewFrameData = bitmapConverter.convertToNV21(resizedPreviewImage);
} catch (Exception e) {
Log.e("DisabledCameraFrameProvider", "Failed to loadPreviewFrame");
}
}
class BitmapConverter {
byte [] convertToNV21(Bitmap bitmap) {
int inputWidth = bitmap.getWidth();
int inputHeight = bitmap.getHeight();
int [] argb = new int[inputWidth * inputHeight];
bitmap.getPixels(argb, 0, inputWidth, 0, 0, inputWidth, inputHeight);
byte [] yuv = new byte[inputWidth*inputHeight*3/2];
encodeYUV420SP(yuv, argb, inputWidth, inputHeight);
bitmap.recycle();
return yuv;
}
void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width, int height) {
final int frameSize = width * height;
int yIndex = 0;
int uvIndex = frameSize;
int R, G, B, Y, U, V;
int index = 0;
for (int j = 0; j < height; j++) {
for (int i = 0; i < width; i++) {
R = (argb[index] & 0xff0000) >> 16;
G = (argb[index] & 0xff00) >> 8;
B = (argb[index] & 0xff);
Y = ( ( 66 * R + 129 * G + 25 * B + 128) >> 8) + 16;
U = ( ( -38 * R - 74 * G + 112 * B + 128) >> 8) + 128;
V = ( ( 112 * R - 94 * G - 18 * B + 128) >> 8) + 128;
yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0 : ((Y > 255) ? 255 : Y));
if (j % 2 == 0 && index % 2 == 0) {
yuv420sp[uvIndex++] = (byte)((V<0) ? 0 : ((V > 255) ? 255 : V));
yuv420sp[uvIndex++] = (byte)((U<0) ? 0 : ((U > 255) ? 255 : U));
}
index ++;
}
}
}
}
Then finally in your callback;
public void onPreviewFrame(byte[] data, Camera camera) {
byte[] bytes = data;
if (!mProvider.isVideoEnabled()) {
Camera.Size previewSize = camera.getParameters().getPreviewSize();
bytes = mProvider.getPreviewFrameData(previewSize.width, previewSize.height);
}
ProvideCameraFrame(bytes, bytes.length, context);
}
The key was to scale the image to the camera preview size and convert the image to YUV colour space.