【发布时间】：2014-03-10 23:05:41
【问题描述】：
以下是我正在尝试的代码。启动器活动正在使用 CamPreview 类。在实现 PreviewCallback 之前，我能够很好地预览。当我通过实现 onPreviewFrame 来尝试 PreviewCallback 时，我完全不知道它是如何在内部工作的。以下是以下让我感到困惑的事情。请澄清它们。
1) 虽然我设置了 ImageFormat 和 Previewsize 等相机参数，但它们似乎不会持续到调用 onPreviewFrame 方法。例如，surfaceChanged 方法中的 Log.i 语句（根据我的理解，在 surfaceCreated 之后至少立即调用一次）将预览大小打印为 1056x864。但是，onPreviewFrame 报告预览大小为 1920x1080。
甚至图片格式从 NV21（surfaceChanged 中的 17）变为 JPEG（onPreviewFrame 中的 256）。
我已经验证并确认传递给onPreviewFrame的Camera实例与CamPreview类中声明的成员变量mCamera相同。
如果我能够在 onPreviewFrame 中成功获得 NV21 的预览格式，我该如何将其转换为 ARGB 格式？我已经尝试过在 stackoverflow 中发布的方法，但是由于索引超出范围，传递给 onPreviewFrame 的数据失败，这导致我首先检查图像格式。如果有人尝试过类似的事情，请让我知道我在创建过程中缺少什么导致这个混乱:(。
我试图通过最初从传递给 onPreviewFrame 的 byte[] 创建 YuvImage 来创建位图，这给了我绿色的后期图像（有时都是绿色或垃圾）！
2) 您可以在我在第 (1) 点中提到的那些旁边看到其他 Log.i stmts。他们在方法surfaceChanged和onPreviewFrame中打印出预览的每像素位和每像素字节信息。结果分别是 12 和 1。这怎么可能呢 ？同样，这可能是 (1) 中发生的事情的副作用
public class CamPreview extends SurfaceView implements SurfaceHolder.Callback, Camera.PreviewCallback {
private static final String TAG = "CamPreview";
private SurfaceHolder mHolder;
private Camera mCamera;
private byte[] mVideoSource;
private Bitmap mBackBuffer;
private Paint mPaint;
private Context mContext;
public CamPreview(Context context) {
super(context);
mContext = context;
mCamera = getCameraInstance();
mHolder = getHolder();
mHolder.addCallback(this);
}
public void surfaceCreated(SurfaceHolder holder) {
try {
mCamera.setDisplayOrientation(90);
mCamera.setPreviewDisplay(null);
mCamera.setPreviewCallbackWithBuffer(this);
this.setWillNotDraw(false);
Log.i(TAG, "@SurfaceCreated: initilization finished");
} catch (IOException eIOException) {
Log.i(TAG, "Error setting camera preview: " + eIOException.getMessage());
throw new IllegalStateException();
}
}
private Size findBestResolution(int pWidth, int pHeight) {
List<Size> lSizes = mCamera.getParameters().getSupportedPreviewSizes();
Size lSelectedSize = mCamera.new Size(0, 0);
for (Size lSize : lSizes) {
if ((lSize.width <= pWidth)
&& (lSize.height <= pHeight)
&& (lSize.width >= lSelectedSize.width)
&& (lSize.height >= lSelectedSize.height)) {
lSelectedSize = lSize;
}
}
if ((lSelectedSize.width == 0)
|| (lSelectedSize.height == 0)) {
lSelectedSize = lSizes.get(0);
}
return lSelectedSize;
}
private void createBuffers(String caller, Size prefSize) {
Camera.Parameters camParams = mCamera.getParameters();
int previewWidth = prefSize.width;
int previewHeight = prefSize.height;
mBackBuffer = Bitmap.createBitmap(previewWidth,
previewHeight,
Bitmap.Config.ARGB_8888);
Log.i(TAG,"@"+caller+": Piture Width " + Integer.toString(previewWidth));
Log.i(TAG,"@"+caller+": Piture Height " + Integer.toString(previewHeight));
Log.i(TAG,"@"+caller+": Piture format " + Integer.toString(ImageFormat.NV21));
camParams.setPreviewSize(previewWidth,previewHeight);
camParams.setPreviewFormat(ImageFormat.NV21);
mCamera.setParameters(camParams);
PixelFormat pxlFrmt = new PixelFormat();
PixelFormat.getPixelFormatInfo(camParams.getPreviewFormat(), pxlFrmt);
Log.i(TAG,"@"+caller+": Bits per pixel " + Integer.toString(pxlFrmt.bitsPerPixel));
Log.i(TAG,"@"+caller+": Bytes per pixel " + Integer.toString(pxlFrmt.bytesPerPixel));
int sz = previewWidth * previewHeight * pxlFrmt.bitsPerPixel/8;
mVideoSource = new byte[sz];
mCamera.addCallbackBuffer(mVideoSource);
Log.i(TAG, "@"+caller+": backbuffer initilization finished");
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.startPreview();
Log.i(TAG, "@SurfaceCreated: preview started");
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null) {
Log.i(TAG,"No proper holder");
return;
}
try {
mCamera.stopPreview();
} catch (Exception e){
Log.i(TAG,"tried to stop a non-existent preview");
return;
}
createBuffers("surfaceChanged",findBestResolution(w, h));
}
public void onPreviewFrame(byte[] data, Camera camera) {
Log.i(TAG,"@onPreviewFrame: Invoked");
Camera.Parameters params = camera.getParameters();
Camera.Size camSize = params.getPictureSize();
int w = camSize.width;
int h = camSize.height;
Log.i(TAG,"@onPreviewFrame: Piture Width " + Integer.toString(w));
Log.i(TAG,"@onPreviewFrame: Piture Height " + Integer.toString(h));
Log.i(TAG,"@onPreviewFrame: Piture format " + Integer.toString(params.getPictureFormat()));
PixelFormat pxlFrmt = new PixelFormat();
PixelFormat.getPixelFormatInfo(params.getPreviewFormat(), pxlFrmt);
Log.i(TAG,"@onPreviewFrame: Bits per pixel " + Integer.toString(pxlFrmt.bitsPerPixel));
Log.i(TAG,"@onPreviewFrame: Bytes per pixel " + Integer.toString(pxlFrmt.bytesPerPixel));
mBackBuffer = BitmapFactory.decodeByteArray(data, 0, data.length);
Log.i(TAG,"@onPreviewFrame: Back buffer set.");
invalidate();
}
@Override
protected void onDraw(Canvas pCanvas) {
super.onDraw(pCanvas);
Log.i(TAG,"@onDraw: Invoked");
if (mCamera != null) {
Log.i(TAG,"@onDraw: Bbefore draw call to canvas");
pCanvas.drawBitmap(mBackBuffer, 0, 0, mPaint);
mCamera.addCallbackBuffer(mVideoSource);
Log.i(TAG,"@onDraw: Draw finished");
}
}
/** Check if this device has a camera */
private boolean checkCameraHardware(Context context) {
if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
// this device has a camera
return true;
} else {
// no camera on this device
return false;
}
}
/** A safe way to get an instance of the Camera object. */
private Camera getCameraInstance(){
Camera c = null;
if(checkCameraHardware(mContext)) {
try {
Log.i(TAG, "Trying to open the camera");
c = Camera.open(0);
Log.i(TAG, "Camera opened successfully.");
}
catch (Exception e){
Log.i(TAG, e.getMessage());
}
}
return c;
}
private void releaseCamera(){
if (mCamera != null){
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
if (mCamera != null) {
mCamera.stopPreview();
releaseCamera();
mVideoSource = null;
mBackBuffer = null;
}
}
}
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