Android camera preview is dark

I am trying to create a custom camera app. I followed the Android Developer example from here with minor tweaks. However, my camera preview turns out to be rather dark. On the other hand, the stock camera gives a much brighter preview.

I have tried several settings to make it work better but it seems none of them are having any impact. Relevant code is posted here.

CameraActivity (Main)

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_camera);
    if(CameraHelper.checkCameraHardware(this)) {
        mHelper = new CameraHelper(this, getWindowManager().getDefaultDisplay());
    }

    FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
    mPreview = new CameraPreview(this, CameraHelper.camera);
    mPreview.setLayoutParams(new LayoutParams(CameraHelper.mSize.width, CameraHelper.mSize.height, Gravity.CENTER));

    preview.addView(mPreview);

}

CameraHelper class (initialize the camera and set the default parameters)

    public CameraHelper(CameraListener listener, Display display){
        mListener = listener;
        camera = getCameraInstance();

        mParameters = camera.getParameters();
        initCameraParameters();

        mSize = getPreviewSize(display);
        mParameters.setFocusMode(Parameters.FOCUS_MODE_AUTO);
        mParameters.setPictureSize(2560, 1920);

        mParameters.setAutoExposureLock(false);
        mParameters.setAutoWhiteBalanceLock(false);
        mParameters.set("iso", "ISO800"); //Tried with 400, 800, 600 (values obtained from flatten())
        mParameters.setColorEffect("none");
        mParameters.setPictureSize(2560, 1920);
        mParameters.setPreviewFrameRate(20);
        mParameters.set("scene-mode", "auto");
        mParameters.setFocusMode("auto");
        mParameters.setExposureCompensation(4);     
        camera.setParameters(mParameters);
    }

The Camera sends the frames to SurfaceHolder.Surface from the example linked from developer pages above.

See the difference here: Stock Camera App My Camera App

Tried setting the ISO, etc based on upack parameters from the camera as posted here. It still didn't work.

Parameters(16369): effect-values=none,mono,negative,sepia,aqua,sharpen,purple,green-tint,blue-tint,pink,yellow,red-tint,mono,antique;exposure-compensation-step=0.5;focal-length=3.43;focus-areas=(0,0,0,0,0);focus-distances=0.10,1.20,Infinity;focus-mode-values=auto,macro,facedetect;gps-altitude=0;gps-latitude=0;gps-longitude=0;gps-processing-method=GPS;gps-timestamp=0;horizontal-view-angle=51.2;iso=auto;iso-values=auto,ISO50,ISO100,ISO200,ISO400,ISO800,ISO1600;jpeg-quality=1;jpeg-thumbnail-height=480;jpeg-thumbnail-size-values=640x480,0x0;jpeg-thumbnail-width=640;max-exposure-compensation=4;max-num-focus-areas=1;max-zoom=12;min-exposure-compensation=-4;picture-format=jpeg;picture-format-values=jpeg;picture-size-values=2560x1920,2560x1536,2048x1536,2048x1232,1600x1200,1600x960,800x480,640x480;preview-format=yuv420sp;preview-format-values=yuv420sp;preview-fps-range=15000,30000;preview-fps-range-values=(15000,30000);preview-frame-rate=30;preview-frame-rate-values=30;preview-size=640x480;preview-size-values=1280x720,800x480,720x480,640x480,352x288;rotation=0;scene-mode=auto;scene-mode-values=auto,portrait,landscape,night,beach,snow,sunset,fireworks,sports,party,candlelight,asd,backlight,dusk-dawn,text,fall-color;vertical-view-angle=39.4;video-frame-format=yuv422i-yuyv;whitebalance-values=auto,incandescent,fluorescent,daylight,cloudy-daylight;zoom=0;zoom-ratios=100,125,150,175,200,225,250,275,300,325,350,375,400;zoom-supported=true;focus-mode=auto;picture-size=2560x1920;exposure-compensation=4;

Edit: Upon further testing based on comments below, it appears that its just the preview that is turning out darker than it should be. The actual captured image is well lit and exposure compensatiion seems to be working fine. Its just the preview that is giving me a headache. Tested on i9003 running CM11 and Nexus 10 running stock android.