Android中Bitmap,byte[],Drawable相互转化

一、相关概念
1、Drawable就是一个可画的对象，其可能是一张位图（BitmapDrawable），也可能是一个图形（ShapeDrawable），还有可能是一个图层（LayerDrawable），我们根据画图的需求，创建相应的可画对象
2、Canvas画布，绘图的目的区域，用于绘图
3、Bitmap位图，用于图的处理
4、Matrix矩阵
二、Bitmap
1、从资源中获取Bitmap
     Resources res = getResources();
     Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.icon);

2、Bitmap → byte[]
1     public byte[] Bitmap2Bytes(Bitmap bm) {
2         ByteArrayOutputStream baos = new ByteArrayOutputStream();
3         bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
4         return baos.toByteArray();
5     }

3、byte[] → Bitmap

     public Bitmap Bytes2Bimap(byte[] b) {
         if (b.length != 0) {
             return BitmapFactory.decodeByteArray(b, 0, b.length);
         } else {
             return null;
         }
     }

4、Bitmap缩放
1     public static Bitmap zoomBitmap(Bitmap bitmap, int width, int height) {
2         int w = bitmap.getWidth();
3         int h = bitmap.getHeight();
4         Matrix matrix = new Matrix();
5         float scaleWidth = ((float) width / w);
6         float scaleHeight = ((float) height / h);
7         matrix.postScale(scaleWidth, scaleHeight);
8         Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true);
9         return newbmp;
10     }

5、将Drawable转化为Bitmap
public static Bitmap drawableToBitmap(Drawable drawable) {
         // 取 drawable 的长宽
         int w = drawable.getIntrinsicWidth();
         int h = drawable.getIntrinsicHeight();

         // 取 drawable 的颜色格式
         Bitmap.Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
                 : Bitmap.Config.RGB_565;
         // 建立对应 bitmap
         Bitmap bitmap = Bitmap.createBitmap(w, h, config);
         // 建立对应 bitmap 的画布
         Canvas canvas = new Canvas(bitmap);
         drawable.setBounds(0, 0, w, h);
         // 把 drawable 内容画到画布中
         drawable.draw(canvas);
         return bitmap;
     }

6、获得圆角图片 
1     public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) {
2         int w = bitmap.getWidth();
3         int h = bitmap.getHeight();
4         Bitmap output = Bitmap.createBitmap(w, h, Config.ARGB_8888);
5         Canvas canvas = new Canvas(output);
6         final int color = 0xff424242;
7         final Paint paint = new Paint();
8         final Rect rect = new Rect(0, 0, w, h);
9         final RectF rectF = new RectF(rect);
10         paint.setAntiAlias(true);
11         canvas.drawARGB(0, 0, 0, 0);
12         paint.setColor(color);
13         canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
14         paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
15         canvas.drawBitmap(bitmap, rect, rect, paint);
16 
17         return output;
18     }

7、获得带倒影的图片

     public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) {
         final int reflectionGap = 4;
         int w = bitmap.getWidth();
         int h = bitmap.getHeight();

         Matrix matrix = new Matrix();
         matrix.preScale(1, -1);

         Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, h / 2, w,
                 h / 2, matrix, false);

         Bitmap bitmapWithReflection = Bitmap.createBitmap(w, (h + h / 2),
                 Config.ARGB_8888);

         Canvas canvas = new Canvas(bitmapWithReflection);
         canvas.drawBitmap(bitmap, 0, 0, null);
         Paint deafalutPaint = new Paint();
         canvas.drawRect(0, h, w, h + reflectionGap, deafalutPaint);

         canvas.drawBitmap(reflectionImage, 0, h + reflectionGap, null);

         Paint paint = new Paint();
         LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
                 bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
                 0x00ffffff, TileMode.CLAMP);
         paint.setShader(shader);
         // Set the Transfer mode to be porter duff and destination in
         paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
         // Draw a rectangle using the paint with our linear gradient
         canvas.drawRect(0, h, w, bitmapWithReflection.getHeight()
                 + reflectionGap, paint);

         return bitmapWithReflection;
     }

三、Drawable
1、Bitmap转换成Drawable
1 Bitmap bm=xxx; //xxx根据你的情况获取
2 BitmapDrawable bd= new BitmapDrawable(getResource(), bm); 
3 因为BtimapDrawable是Drawable的子类，最终直接使用bd对象即可。
2、Drawable缩放

     public static Drawable zoomDrawable(Drawable drawable, int w, int h) {
         int width = drawable.getIntrinsicWidth();
         int height = drawable.getIntrinsicHeight();
         // drawable转换成bitmap
         Bitmap oldbmp = drawableToBitmap(drawable);
         // 创建操作图片用的Matrix对象
         Matrix matrix = new Matrix();
         // 计算缩放比例
         float sx = ((float) w / width);
         float sy = ((float) h / height);
         // 设置缩放比例
         matrix.postScale(sx, sy);
         // 建立新的bitmap，其内容是对原bitmap的缩放后的图
         Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height,
                 matrix, true);
         return new BitmapDrawable(newbmp);
     }

原文： http://www.eoeandroid.com/thread-167281-1-1.html