Bitmap:
Bitmap是Android系統中的圖像處理的最重要類之一。用它可以獲取圖像文件信息,進行圖像剪切、旋轉、縮放等操作,並可以指定格式保存圖像文件。
重要函數
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public void recycle() // 回收位圖佔用的內存空間,把位圖標記爲Dead
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public final boolean isRecycled() //判斷位圖內存是否已釋放
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public final int getWidth()//獲取位圖的寬度
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public final int getHeight()//獲取位圖的高度
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public final boolean isMutable()//圖片是否可修改
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public int getScaledWidth(Canvas canvas)//獲取指定密度轉換後的圖像的寬度
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public int getScaledHeight(Canvas canvas)//獲取指定密度轉換後的圖像的高度
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public boolean compress(CompressFormat format, int quality, OutputStream stream)//按指定的圖片格式以及畫質,將圖片轉換爲輸出流。
format:Bitmap.CompressFormat.PNG或Bitmap.CompressFormat.JPEG
quality:畫質,0-100.0表示最低畫質壓縮,100以最高畫質壓縮。對於PNG等無損格式的圖片,會忽略此項設置。
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public static Bitmap createBitmap(Bitmap src) //以src爲原圖生成不可變得新圖像
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public static Bitmap createScaledBitmap(Bitmap src, int dstWidth, int dstHeight, boolean filter)//以src爲原圖,創建新的圖像,指定新圖像的高寬以及是否可變。
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public static Bitmap createBitmap(int width, int height, Config config)——創建指定格式、大小的位圖
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public static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height)以source爲原圖,創建新的圖片,指定起始座標以及新圖像的高寬。
BitmapFactory工廠類:
Option 參數類:
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public boolean inJustDecodeBounds//如果設置爲true,不獲取圖片,不分配內存,但會返回圖片的高度寬度信息。
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public int inSampleSize//圖片縮放的倍數
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public int outWidth//獲取圖片的寬度值
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public int outHeight//獲取圖片的高度值
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public int inDensity//用於位圖的像素壓縮比
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public int inTargetDensity//用於目標位圖的像素壓縮比(要生成的位圖)
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public byte[] inTempStorage //創建臨時文件,將圖片存儲
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public boolean inScaled//設置爲true時進行圖片壓縮,從inDensity到inTargetDensity
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public boolean inDither //如果爲true,解碼器嘗試抖動解碼
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public Bitmap.Config inPreferredConfig //設置解碼器
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public String outMimeType //設置解碼圖像
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public boolean inPurgeable//當存儲Pixel的內存空間在系統內存不足時是否可以被回收
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public boolean inInputShareable //inPurgeable爲true情況下才生效,是否可以共享一個InputStream
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public boolean inPreferQualityOverSpeed //爲true則優先保證Bitmap質量其次是解碼速度
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public boolean inMutable //配置Bitmap是否可以更改,比如:在Bitmap上隔幾個像素加一條線段
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public int inScreenDensity //當前屏幕的像素密度
工廠方法:
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public static Bitmap decodeFile(String pathName, Options opts) //從文件讀取圖片
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public static Bitmap decodeFile(String pathName)
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public static Bitmap decodeStream(InputStream is) //從輸入流讀取圖片
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public static Bitmap decodeStream(InputStream is, Rect outPadding, Options opts)
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public static Bitmap decodeResource(Resources res, int id) //從資源文件讀取圖片
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public static Bitmap decodeResource(Resources res, int id, Options opts)
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public static Bitmap decodeByteArray(byte[] data, int offset, int length) //從數組讀取圖片
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public static Bitmap decodeByteArray(byte[] data, int offset, int length, Options opts)
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public static Bitmap decodeFileDescriptor(FileDescriptor fd)//從文件讀取文件 與decodeFile不同的是這個直接調用JNI函數進行讀取 效率比較高
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public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts)
Bitmap.Config inPreferredConfig :
枚舉變量 (位圖位數越高代表其可以存儲的顏色信息越多,圖像越逼真,佔用內存越大)
- public static final Bitmap.Config ALPHA_8 //代表8位Alpha位圖 每個像素佔用1byte內存
- public static final Bitmap.Config ARGB_4444 //代表16位ARGB位圖 每個像素佔用2byte內存
- public static final Bitmap.Config ARGB_8888 //代表32位ARGB位圖 每個像素佔用4byte內存
- public static final Bitmap.Config RGB_565 //代表8位RGB位圖 每個像素佔用2byte內存
圖片讀取實例:
1.)從文件讀取方式一
/**
* 獲取縮放後的本地圖片
*
* @param filePath 文件路徑
* @param width 寬
* @param height 高
* @return
*/
public static Bitmap readBitmapFromFile(String filePath, int width, int height) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeFile(filePath, options);
}
2.)從文件讀取方式二 效率高於方式一
/**
* 獲取縮放後的本地圖片
*
* @param filePath 文件路徑
* @param width 寬
* @param height 高
* @return
*/
public static Bitmap readBitmapFromFileDescriptor(String filePath, int width, int height) {
try {
FileInputStream fis = new FileInputStream(filePath);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFileDescriptor(fis.getFD(), null, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeFileDescriptor(fis.getFD(), null, options);
} catch (Exception ex) {
}
return null;
}
測試同樣生成10張圖片兩種方式耗時比較 cpu使用以及內存佔用兩者相差無幾 第二種方式效率高一點 所以建議優先採用第二種方式
start = System.currentTimeMillis();
for (int i = 0; i < testMaxCount; i++) {
BitmapUtils.readBitmapFromFile(filePath, 400, 400);
}
end = System.currentTimeMillis();
Log.e(TAG, "BitmapFactory decodeFile--time-->" + (end - start));
start = System.currentTimeMillis();
for (int i = 0; i < testMaxCount; i++) {
BitmapUtils.readBitmapFromFileDescriptor(filePath, 400, 400);
}
end = System.currentTimeMillis();
Log.e(TAG, "BitmapFactory decodeFileDescriptor--time-->" + (end - start));
3.)從輸入流中讀取文件
/**
* 獲取縮放後的本地圖片
*
* @param ins 輸入流
* @param width 寬
* @param height 高
* @return
*/
public static Bitmap readBitmapFromInputStream(InputStream ins, int width, int height) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(ins, null, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeStream(ins, null, options);
}
4.)從資源文件中讀取文件
public static Bitmap readBitmapFromResource(Resources resources, int resourcesId, int width, int height) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(resources, resourcesId, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeResource(resources, resourcesId, options);
}
此種方式相當的耗費內存 建議採用decodeStream代替decodeResource 可以如下形式
public static Bitmap readBitmapFromResource(Resources resources, int resourcesId, int width, int height) {
InputStream ins = resources.openRawResource(resourcesId);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(ins, null, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeStream(ins, null, options);
}
decodeStream、decodeResource佔用內存對比:
start = System.currentTimeMillis();
for (int i = 0; i < testMaxCount; i++) {
BitmapUtils.readBitmapFromResource(getResources(), R.mipmap.ic_app_center_banner, 400, 400);
Log.e(TAG, "BitmapFactory decodeResource--num-->" + i);
}
end = System.currentTimeMillis();
Log.e(TAG, "BitmapFactory decodeResource--time-->" + (end - start));
start = System.currentTimeMillis();
for (int i = 0; i < testMaxCount; i++) {
BitmapUtils.readBitmapFromResource1(getResources(), R.mipmap.ic_app_center_banner, 400, 400);
Log.e(TAG, "BitmapFactory decodeStream--num-->" + i);
}
end = System.currentTimeMillis();
Log.e(TAG, "BitmapFactory decodeStream--time-->" + (end - start));
BitmapFactory.decodeResource 加載的圖片可能會經過縮放,該縮放目前是放在 java 層做的,效率比較低,而且需要消耗 java 層的內存。因此,如果大量使用該接口加載圖片,容易導致OOM錯誤
BitmapFactory.decodeStream 不會對所加載的圖片進行縮放,相比之下佔用內存少,效率更高。
這兩個接口各有用處,如果對性能要求較高,則應該使用 decodeStream;如果對性能要求不高,且需要 Android 自帶的圖片自適應縮放功能,則可以使用 decodeResource。
5. )從二進制數據讀取圖片
public static Bitmap readBitmapFromByteArray(byte[] data, int width, int height) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeByteArray(data, 0, data.length, options);
float srcWidth = options.outWidth;
float srcHeight = options.outHeight;
int inSampleSize = 1;
if (srcHeight > height || srcWidth > width) {
if (srcWidth > srcHeight) {
inSampleSize = Math.round(srcHeight / height);
} else {
inSampleSize = Math.round(srcWidth / width);
}
}
options.inJustDecodeBounds = false;
options.inSampleSize = inSampleSize;
return BitmapFactory.decodeByteArray(data, 0, data.length, options);
}
6.)從assets文件讀取圖片
/**
* 獲取縮放後的本地圖片
*
* @param filePath 文件路徑
* @return
*/
public static Bitmap readBitmapFromAssetsFile(Context context, String filePath) {
Bitmap image = null;
AssetManager am = context.getResources().getAssets();
try {
InputStream is = am.open(filePath);
image = BitmapFactory.decodeStream(is);
is.close();
} catch (IOException e) {
e.printStackTrace();
}
return image;
}
圖片保存文件:
public static void writeBitmapToFile(String filePath, Bitmap b, int quality) {
try {
File desFile = new File(filePath);
FileOutputStream fos = new FileOutputStream(desFile);
BufferedOutputStream bos = new BufferedOutputStream(fos);
b.compress(Bitmap.CompressFormat.JPEG, quality, bos);
bos.flush();
bos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
圖片壓縮:
private static Bitmap compressImage(Bitmap image) {
if (image == null) {
return null;
}
ByteArrayOutputStream baos = null;
try {
baos = new ByteArrayOutputStream();
image.compress(Bitmap.CompressFormat.JPEG, 100, baos);
byte[] bytes = baos.toByteArray();
ByteArrayInputStream isBm = new ByteArrayInputStream(bytes);
Bitmap bitmap = BitmapFactory.decodeStream(isBm);
return bitmap;
} catch (OutOfMemoryError e) {
} finally {
try {
if (baos != null) {
baos.close();
}
} catch (IOException e) {
}
}
return null;
}
圖片縮放:
/**
* 根據scale生成一張圖片
*
* @param bitmap
* @param scale 等比縮放值
* @return
*/
public static Bitmap bitmapScale(Bitmap bitmap, float scale) {
Matrix matrix = new Matrix();
matrix.postScale(scale, scale); // 長和寬放大縮小的比例
Bitmap resizeBmp = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
return resizeBmp;
}
獲取圖片旋轉角度:
/**
* 讀取照片exif信息中的旋轉角度
*
* @param path 照片路徑
* @return角度
*/
private static int readPictureDegree(String path) {
if (TextUtils.isEmpty(path)) {
return 0;
}
int degree = 0;
try {
ExifInterface exifInterface = new ExifInterface(path);
int orientation = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_90:
degree = 90;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
degree = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_270:
degree = 270;
break;
}
} catch (Exception e) {
}
return degree;
}
更多內容,請看這裏:http://www.cnblogs.com/whoislcj/p/5547758.html