1.采样率压缩

采样率压缩是改变了图片的像素，他是通过先读取图片的边，然后在自己设定图片的边，然后根据设定，读取图片的像素。在读取的时候，并不是所有的像素都读取，而是由选择的。所以这种方式减少了像素的个数，能改变图片在内存中的占用大小

    /**
     * 采样率压缩
     */
    public static Bitmap inSampleCompress(String filePath,int inSampleSize){
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true; //为True时，不会真正加载图片，而是得到图片的宽高信息
        options.inSampleSize = 1;

        BitmapFactory.decodeFile(filePath, options);

        options.inSampleSize = computeSize(options);
        options.inJustDecodeBounds = false;

        return BitmapFactory.decodeFile(filePath, options);
    }

    // 开源项目 鲁班Luban 的算法
    private static int computeSize(BitmapFactory.Options options) {
        int srcWidth = options.outWidth;
        int srcHeight = options.outHeight;
        srcWidth = srcWidth % 2 == 1 ? srcWidth + 1 : srcWidth;
        srcHeight = srcHeight % 2 == 1 ? srcHeight + 1 : srcHeight;

        int longSide = Math.max(srcWidth, srcHeight);
        int shortSide = Math.min(srcWidth, srcHeight);

        float scale = ((float) shortSide / longSide);
        if (scale <= 1 && scale > 0.5625) {
            if (longSide < 1664) {
                return 1;
            } else if (longSide < 4990) {
                return 2;
            } else if (longSide > 4990 && longSide < 10240) {
                return 4;
            } else {
                return longSide / 1280 == 0 ? 1 : longSide / 1280;
            }
        } else if (scale <= 0.5625 && scale > 0.5) {
            return longSide / 1280 == 0 ? 1 : longSide / 1280;
        } else {
            return (int) Math.ceil(longSide / (1280.0 / scale));
        }
    }

保存Bitmap图片到文件

public static void saveBitmap(Bitmap bitmap,File file){
        ByteArrayOutputStream stream =new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG,100,stream);
        try {
            if (file.exists()){
                file.delete();
            }else{
                file.createNewFile();
            }
            FileOutputStream fileOutputStream=new FileOutputStream(file);
            fileOutputStream.write(stream.toByteArray());
            fileOutputStream.flush();
            fileOutputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

2.尺寸压缩

通过缩放图片的像素，减小图片占用内存大小,这个比如用于缩略图

/**尺寸压缩
 * @param bitmap 要压缩的图片
 * @param ratio 压缩比例，值越大，图片的尺寸就越小
 * @param file 压缩的图片保存地址
 */
public static void sizeCompressBitmap(Bitmap bitmap,int ratio,File file){
    if (ratio<=0){
        return;
    }
    Bitmap result=Bitmap.createBitmap(bitmap.getWidth()/ratio,bitmap.getHeight()/ratio, Bitmap.Config.ARGB_8888);
    Canvas canvas =new Canvas();
    Rect rect=new Rect(0,0,bitmap.getWidth()/ratio,bitmap.getHeight()/ratio);
    canvas.drawBitmap(bitmap,null,rect,null);
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    // 把压缩后的数据存放到baos中
    result.compress(Bitmap.CompressFormat.JPEG, 100 ,baos);
    try {
        FileOutputStream fos = new FileOutputStream(file);
        fos.write(baos.toByteArray());
        fos.flush();
        fos.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

3.质量压缩

质量压缩,这个只是降低了图片的质量，但是像素是不会减小的

 /** 质量压缩,
     * @param bitmap 要压缩的图片
     * @param file //压缩的图片保存地址
     *  Hint to the compressor, 0-100. 0 meaning compress for small size, 100 meaning compress for max quality. Some
     * formats, like PNG which is lossless, will ignore the quality setting
     * quality  (0-100)  100是不压缩，值越小，压缩得越厉害
     */
    public static void qualityCompressBitmap(Bitmap bitmap,File file){
        //字节数组输出流
        ByteArrayOutputStream baos =new ByteArrayOutputStream();
        int quality=60;
        //图片压缩后把数据放在stream中
        bitmap.compress(Bitmap.CompressFormat.JPEG,quality, baos);

//        int quality = 80;
//        while (baos.toByteArray().length > MAX_SIZE) {
//            baos.reset();
//            bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos);
//            quality -= 10;
//            if(quality < 50){
//                break;
//            }
//        }
        try {
            FileOutputStream fileOutputStream=new FileOutputStream(file);
            fileOutputStream.write(baos.toByteArray());
            fileOutputStream.flush();
            fileOutputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

4.旋转图片

private static Bitmap rotatingImage(Bitmap bitmap, int degree) {
        Matrix matrix = new Matrix();
        matrix.postRotate(degree);

        return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
    }

    /**
     *
     * 读取图片属性：旋转的角度
     * @param path 图片绝对路径
     * @return degree旋转的角度
     */

    public static int readPictureDegree(String path) {
        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 (IOException e) {
            e.printStackTrace();
        }
        return degree;
    }