Android Camera预览画面变形问题

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问题

安卓camera1在预览时，预览画面看起来被拉伸了．
如图，圆形的盖子，变成椭圆形了．

代码

默认流程，如下为大致的打开摄像头并进行预览显示的代码

private Camera mCamera = null;
private SurfaceView mSurfaceView = null;
private SurfaceHolder holder = null;


mSurfaceView = (SurfaceView) findViewById(R.id.surfaceView);
holder = mSurfaceView.getHolder();
holder.addCallback(this);
holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

mCamera = Camera.open(mCameraId);
// .... 中间设置方向等省略
mCamera.setPreviewDisplay(holder);
mCamera.startPreview();

解决

1. 网上大部分的解决方法(实测不一定有效)
   原理是遍历摄像头分辨率，找到与当前屏幕契合的分辨率，并设置为预览大小．
   如下代码，getOptimalPreviewSize的调用放在上面的mCamera.startPreview();之前．

Camera.Parameters parameters = null;
parameters = mCamera.getParameters();
DisplayMetrics dm = getResources().getDisplayMetrics();
List<Size> previewSizes = parameters.getSupportedPreviewSizes();
Size previewSize = getOptimalPreviewSize(previewSizes, dm.widthPixels, dm.heightPixels);
parameters.setPreviewSize(previewSize.width, previewSize.height);

private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
    final double ASPECT_TOLERANCE = 0.1;
    double targetRatio = (double) w / h;
    if (sizes == null)
        return null;

    Size optimalSize = null;
    double minDiff = Double.MAX_VALUE;

    int targetHeight = h;

    // Try to find an size match aspect ratio and size
    for (Size size : sizes) {
        double ratio = (double) size.width / size.height;
        if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE)
            continue;
        int tempDiff = Math.abs(size.height - targetHeight);
        if (tempDiff < minDiff) {
            optimalSize = size;
            minDiff = tempDiff;
        }
    }

    // Cannot find the one match the aspect ratio, ignore the requirement
    if (optimalSize == null) {
        minDiff = Double.MAX_VALUE;
        for (Size size : sizes) {
            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }
    }
    return optimalSize;
}

2. 实测可用方法
   把摄像头预览大小设置成屏幕显示大小，在mCamera.startPreview()调用如下代码

public static void setCameraPreviewSize(Camera camera) {
    WindowManager manager = (WindowManager) FactoryTestApplication.getContext().getSystemService(Context.WINDOW_SERVICE);
    Display display = manager.getDefaultDisplay();
    Parameters parameters = camera.getParameters();
    parameters.setPreviewSize(display.getHeight(), display.getWidth());
    camera.setParameters(parameters);
}

显示正常图如下

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