Android Bitmap在不載入圖片的前提擷取寬高

Android Bitmap在不載入圖片的前提擷取寬高

代碼參考：

 

 /**      * 根據View(主要是ImageView)的寬和高來擷取圖片的縮圖      * @param path      * @param viewWidth      * @param viewHeight      * @return      */      private Bitmap decodeThumbBitmapForFile(String path, int viewWidth, int viewHeight){          BitmapFactory.Options options = new BitmapFactory.Options();          //設定為true,表示解析Bitmap對象，該對象不佔記憶體          options.inJustDecodeBounds = true;          BitmapFactory.decodeFile(path, options);          //設定縮放比例          options.inSampleSize = computeScale(options, viewWidth, viewHeight);                    //設定為false,解析Bitmap對象加入到記憶體中          options.inJustDecodeBounds = false;                    return BitmapFactory.decodeFile(path, options);      }                  /**      * 根據View(主要是ImageView)的寬和高來計算Bitmap縮放比例。預設不縮放      * @param options      * @param width      * @param height      */      private int computeScale(BitmapFactory.Options options, int viewWidth, int viewHeight){          int inSampleSize = 1;          if(viewWidth == 0 || viewHeight == 0){              return inSampleSize;          }          int bitmapWidth = options.outWidth;          int bitmapHeight = options.outHeight;                    //假如Bitmap的寬度或高度大於我們設定圖片的View的寬高，則計算縮放比例          if(bitmapWidth > viewWidth || bitmapHeight > viewWidth){              int widthScale = Math.round((float) bitmapWidth / (float) viewWidth);              int heightScale = Math.round((float) bitmapHeight / (float) viewWidth);                            //為了保證圖片不縮放變形，我們取寬高比例最小的那個              inSampleSize = widthScale < heightScale ? widthScale : heightScale;          }          return inSampleSize;      }        

另外可參照：

 

 

BitmapFactory.Options options = new BitmapFactory.Options();                  /**         * 最關鍵在此，把options.inJustDecodeBounds = true;         * 這裡再decodeFile()，返回的bitmap為空白，但此時調用options.outHeight時，已經包含了圖片的高了         */         options.inJustDecodeBounds = true;         Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/test.jpg", options); // 此時返回的bitmap為null         /**         *options.outHeight為原始圖片的高         */         Log.e("Test", "Bitmap Height == " + options.outHeight);  

根據這些方法，可以在實際載入Bitmap圖片之前根據需要設定圖片縮小為原來的（1/2,1/4,1/8,1/16..）

 

下面是Android源碼中關於 inSampleSize的說明:

 

public int inSampleSizeAdded in API level 1If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory. The sample size is the number of pixels in either dimension that correspond to a single pixel in the decoded bitmap. For example, inSampleSize == 4 returns an image that is 1/4 the width/height of the original, and 1/16 the number of pixels. Any value <= 1 is treated the same as 1. Note: the decoder uses a final value based on powers of 2, any other value will be rounded down to the nearest power of 2.