Almost all mobile phones have a built in digital camera. Android phones are no exception. In Android device, to access the camera hardware we use
Camera class along with
The Camera class let you change the settings, preview and take still pictures. The SurfaceView class is used to show the preview to the user. To use the camera feature you should have the android.permission.CAMERA permission.
First we create a SurfaceView to show the live preview. The SurfaceView class holds the surface to draw. We use the interface SurfaceHolder to access the underlying surface. We implement the callback interface SurfaceHolfer.Callback and add this to the SurfaceHolder using SurfaceHolder.addCallback method. The SurfaceHolfer.Callback interface has three methods:
abstract void surfaceChanged(SurfaceHolder holder, int format, int width, int height) abstract void surfaceCreated(SurfaceHolder holder) abstract void surfaceDestroyed(SurfaceHolder holder)
The surfaceCreated method will be called after the surface is created, surfaceChanged will be after any changes have been made to the surface and surfaceDestroyed will be called after the surface is destroyed.
To find more about the SurfaceView and SurfaceHolder interface refer to the Google documentation.
Once our surface is created we open the Camera using Camera.open() method. After opening the camera, we set the live preview surface using
setPreviewDisplay() method of the Camera class. We open and set the preview surface once the
surfaceCreated() method is called because at this point the surface will be created and initialized properly.
Now we have to set the appropriate parameters to start the camera using the Camera.Parameters class. We can get the current camera parameter using the
getParameters() method of the Camera class. We set the camera parameter once the
surfaceChaneged() method is called. Once we set all the camera parameters we can start preview using
Camera.startPreview() method. This will start the live preview.
The Camera class uses different callback interface to report different events to the application. The following callback interfaces are used to notify the events;
Camera.AutoFocusCallback Camera.ErrorCallback Camera.PictureCallback Camera.PreviewCallback Camera.ShutterCallback
Camera.AutoFocusCallback interface is used to notify the completion of auto focus. Note that all devices may not have auto-focus feature. The
onAutoFocus() will be called once the auto focus in finished. We use
Camera.autoFocus() method to start the auto focus.
Camera.ErrorCallback interface is used to notify when an error occurred. The
onError() method will be called if an error occurred during the camera operation.
Camera.PictureCallback interface is used to supply the image data after the picture is taken. The
onPictureTaken() method will be called once the data is available. The format of the data depends on the current camera picture format which can be set using Camera.Parameters class.
Camera.PreviewCallback interface is used to notify the supply the current preview frame. The
onPreviewFrame() method will be called when the preview frame is available. Again the format of the data depends on the current camera picture format.
Camera.ShutterCallback interface is to notify when the picture is captured from the camera. The
onShutter() method will be called once the picture is taken from the camera.
To take a still picture, we use the method
Camera.takePicture() The takePicture() method has three parameters. First one is a
Camera.ShutterCallback interface to notify when the picture is captured from the camera. Second one is
Camera.PictureCallback interface to notify when raw data is available from the camera. The third one is another
Camera.PictureCallback interface when the JPEG data is available from the device.
In API version 5 or above there is another variant of
takePicture() method. This method accepts 4 parameters. The first and second are same as the previous one. The third is the
Camera.PictureCallback interface which is used to notify when completely scaled postview image is available. The forth one is the same as the third parameter in the first variant.
The data will be supplied to the calling application, the application can use this data for post processing or saving to a file.
In API version 8 or above, we can use the method
Camera.setDisplayOrientation() method to set the orientation of the display. This is used by portrait applications to correctly display the live preview. In versions prior to 8, we can safely use the landscape mode to correctly display the preview.
The sample application displays the live preview. When the take picture button is clicked the image is saved to sdcard using time as the filename.
Happy Camera Coding