常用轉化成bitmap的方法

Bitmap decodeFile(...)
Bitmap decodeResource(...)
Bitmap decodeByteArray(...)
Bitmap decodeStream(...)
Bitmap decodeFileDescriptor(...)

對圖片質量進行壓縮

        public static Bitmap compressImage(Bitmap bitmap){  
            ByteArrayOutputStream baos = new ByteArrayOutputStream();  
            //質量壓縮方法，這裡100表示不壓縮，把壓縮後的資料存放到baos中  
 

            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, baos);  
            int options = 100;  
            //迴圈判斷如果壓縮後圖片是否大於50kb,大於繼續壓縮  
            while ( baos.toByteArray().length / 1024>50) {  
                //清空baos  
                baos.reset();  
                bitmap.compress(Bitmap.CompressFormat.JPEG, options, baos);  
                options -= 10
 
;//每次都減少10  
            }  
            //把壓縮後的資料baos存放到ByteArrayInputStream中  
            ByteArrayInputStream isBm = new ByteArrayInputStream(baos.toByteArray());  
            //把ByteArrayInputStream資料生成圖片  
            Bitmap newBitmap = BitmapFactory.decodeStream(isBm, null, null);  
            return
 
 newBitmap;  
        }

對圖片尺寸進行壓縮

   /**
     * 按圖片尺寸壓縮 引數是bitmap
     * @param bitmap
     * @param pixelW
     * @param pixelH
     * @return
     */
    public static Bitmap compressImageFromBitmap(Bitmap bitmap, int pixelW, int pixelH) {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, os);
        if( os.toByteArray().length / 1024>512) {//判斷如果圖片大於0.5M,進行壓縮避免在生成圖片（BitmapFactory.decodeStream）時溢位
            os.reset();
            bitmap.compress(Bitmap.CompressFormat.JPEG, 50, os);//這裡壓縮50%，把壓縮後的資料存放到baos中
        }
        ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        options.inPreferredConfig = Bitmap.Config.RGB_565;
        BitmapFactory.decodeStream(is, null, options);
        options.inJustDecodeBounds = false;
        options.inSampleSize = computeSampleSize(options , pixelH > pixelW ? pixelW : pixelH ,pixelW * pixelH );
        is = new ByteArrayInputStream(os.toByteArray());
        Bitmap newBitmap = BitmapFactory.decodeStream(is, null, options);
        return newBitmap;
    }


    /**
     * 動態計算出圖片的inSampleSize
     * @param options
     * @param minSideLength
     * @param maxNumOfPixels
     * @return
     */
    public static int computeSampleSize(BitmapFactory.Options options, int minSideLength, int maxNumOfPixels) {
        int initialSize = computeInitialSampleSize(options, minSideLength, maxNumOfPixels);
        int roundedSize;
        if (initialSize <= 8) {
            roundedSize = 1;
            while (roundedSize < initialSize) {
                roundedSize <<= 1;
            }
        } else {
            roundedSize = (initialSize + 7) / 8 * 8;
        }
        return roundedSize;
    }

    private static int computeInitialSampleSize(BitmapFactory.Options options, int minSideLength, int maxNumOfPixels) {
        double w = options.outWidth;
        double h = options.outHeight;
        int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
        int upperBound = (minSideLength == -1) ? 128 :(int) Math.min(Math.floor(w / minSideLength), Math.floor(h / minSideLength));
        if (upperBound < lowerBound) {
            return lowerBound;
        }
        if ((maxNumOfPixels == -1) && (minSideLength == -1)) {
            return 1;
        } else if (minSideLength == -1) {
            return lowerBound;
        } else {
            return upperBound;
        }
    }