Android image processing: Identify image orientation and display

When you use ImageView to display images in Android, you find that the images are not displayed. The direction is biased or upside down.

To solve the problem it is natural to think of a two-step walk:

1, self-actively identify the direction of the image, calculate the rotation angle.

2, the image is rotated and displayed.

First, identify the direction of the image

First, here is a concept exif (exchangeable image file Format, exchangeable image files ), explained in detail in the wiki.

In short, EXIF is a standard for electronic cameras (including mobile phones, scanners, etc.). Used to standardize pictures, sounds, video screens, and some of their auxiliary markup formats.

The formats supported by EXIF are as follows:

image	uncompressed image file: TIFF	not supported: JPEG 2000, PNG, GIF
audio	RIFF, WAV	 

Android provides support for the EXIF interface of JPEG format images, able to read JPEG file metadata information, see Exifinterface.

These metadata information generally fall into three categories: date time, spatial information (latitude and longitude, height), camera information (aperture, focal length, rotation angle, exposure, etc.).

Second, the image rotation

The operation of matrix rotation on bitmap is provided in Android. See the static CreateBitmap method provided by bitmap.

Public static Bitmap CreateBitmap (Bitmap source, int x, int y, int width, int height, Matrix m, boolean filter)Added in API Level 1

Returns an immutable bitmap from subset of the source bitmap, transformed by the optional matrix. The new bitmap is the same object as source, or a copy may has been made. It is initialized with the same density as the original bitmap. If the source bitmap is immutable and the requested subset are the same as the source bitmap itself, then the source bitmap is returned and no new bitmap is created.

Parameters

Source	The bitmap we are subsetting
X	The X coordinate of the first pixel in source
Y	The Y coordinate of the first pixel in source
Width	The number of pixels in each row
Height	The number of rows
M	Optional matrix to is applied to the pixels
Filter	True if the source should be filtered. Only applies if the matrix contains more than just translation.

Returns

• A bitmap that represents the specified subset of source

Throws

IllegalArgumentException	If the x, y, width, height values are outside of the dimensions of the source bitmap.

Both of these problems have been solved theoretically, so let's start with the actual operation and take a look at the code below.

public class Iohelper {.../** loading a picture from a given path */public static Bitmap LoadBitmap (String imgpath) {return Bitmapfactory.decodefile (Imgpath);} /** loads the picture from the given path and specifies whether to rotate the direction itself */public static Bitmap LoadBitmap (String imgpath, Boolean adjustoritation) {if (! Adjustoritation) {return LoadBitmap (Imgpath),} else {Bitmap BM = LoadBitmap (imgpath); int digree = 0; Exifinterface exif = null;try {exif = new exifinterface (Imgpath);} catch (IOException e) {e.printstacktrace (); exif = null; }if (exif = null) {//Read camera orientation information in picture int ori = Exif.getattributeint (exifinterface.tag_orientation, exifinterface.orientation_undefined);//Calculate rotation angle switch (ORI) {case ExifInterface.ORIENTATION_ROTATE_90:digree = 90; Break;case ExifInterface.ORIENTATION_ROTATE_180:digree = 180;break;case exifinterface.orientation_rotate_270: Digree = 270;break;default:digree = 0;break;}} if (Digree! = 0) {//rotate picture matrix M = new Matrix (); M.postrotate (digree); BM = Bitmap.createbitmap (BM, 0, 0, bm.getwidth (), BM. GetHeight (), M, true);} return BM;}} ......}

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Android image processing: Identify image orientation and display