我們在做專案的時候有時候需要給圖片新增水印，水寒今天就遇到了這樣的問題，所以搞了一個工具類，貼出來大家直接呼叫就行。

/**
 * 圖片工具類
 * @author 水寒
 * 歡迎訪問水寒的個人部落格：http://www.sunhome.org.cn
 *
 */
public class ImageUtil {

    /**
     * 設定水印圖片在左上角
     * @param Context
     * @param src
     * @param watermark
     * @param paddingLeft
     * @param paddingTop
     * @return
 

     */
    public static Bitmap createWaterMaskLeftTop(
            Context context, Bitmap src, Bitmap watermark,
            int paddingLeft, int paddingTop) {
        return createWaterMaskBitmap(src, watermark, 
                dp2px(context, paddingLeft), dp2px(context, paddingTop));
    }

    private
 
 static Bitmap createWaterMaskBitmap(Bitmap src, Bitmap watermark,
            int paddingLeft, int paddingTop) {
        if (src == null) {
            return null;
        }
        int width = src.getWidth();
        int height = src.getHeight();
        //建立一個bitmap
        Bitmap newb = Bitmap.createBitmap(width, height, Config.ARGB_8888);// 建立一個新的和SRC長度寬度一樣的點陣圖
 

        //將該圖片作為畫布
        Canvas canvas = new Canvas(newb);
        //在畫布 0，0座標上開始繪製原始圖片
        canvas.drawBitmap(src, 0, 0, null);
        //在畫布上繪製水印圖片
        canvas.drawBitmap(watermark, paddingLeft, paddingTop, null);
        // 儲存
        canvas.save(Canvas.ALL_SAVE_FLAG);
        // 儲存
        canvas.restore();
        return newb;
    }

    /**
     * 設定水印圖片在右下角
     * @param Context
     * @param src
     * @param watermark
     * @param paddingRight
     * @param paddingBottom
     * @return
     */
    public static Bitmap createWaterMaskRightBottom(
            Context context, Bitmap src, Bitmap watermark,
            int paddingRight, int paddingBottom) {
        return createWaterMaskBitmap(src, watermark, 
                src.getWidth() - watermark.getWidth() - dp2px(context, paddingRight), 
                src.getHeight() - watermark.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 設定水印圖片到右上角
     * @param Context
     * @param src
     * @param watermark
     * @param paddingRight
     * @param paddingTop
     * @return
     */
    public static Bitmap createWaterMaskRightTop(
            Context context, Bitmap src, Bitmap watermark,
            int paddingRight, int paddingTop) {
        return createWaterMaskBitmap( src, watermark, 
                src.getWidth() - watermark.getWidth() - dp2px(context, paddingRight), 
                dp2px(context, paddingTop));
    }

    /**
     * 設定水印圖片到左下角
     * @param Context
     * @param src
     * @param watermark
     * @param paddingLeft
     * @param paddingBottom
     * @return
     */
    public static Bitmap createWaterMaskLeftBottom(
            Context context, Bitmap src, Bitmap watermark,
            int paddingLeft, int paddingBottom) {
        return createWaterMaskBitmap(src, watermark, dp2px(context, paddingLeft), 
                src.getHeight() - watermark.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 設定水印圖片到中間
     * @param Context
     * @param src
     * @param watermark
     * @return
     */
    public static Bitmap createWaterMaskCenter(Bitmap src, Bitmap watermark) {
        return createWaterMaskBitmap(src, watermark, 
                (src.getWidth() - watermark.getWidth()) / 2,
                (src.getHeight() - watermark.getHeight()) / 2);
    }

    /**
     * 給圖片新增文字到左上角
     * @param context
     * @param bitmap
     * @param text
     * @return
     */
    public static Bitmap drawTextToLeftTop(Context context, Bitmap bitmap, String text,
            int size, int color, int paddingLeft, int paddingTop) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds, 
                dp2px(context, paddingLeft),  
                dp2px(context, paddingTop) + bounds.height());
    }

    /**
     * 繪製文字到右下角
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingLeft
     * @param paddingTop
     * @return
     */
    public static Bitmap drawTextToRightBottom(Context context, Bitmap bitmap, String text,
            int size, int color, int paddingRight, int paddingBottom) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds, 
                bitmap.getWidth() - bounds.width() - dp2px(context, paddingRight), 
                bitmap.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 繪製文字到右上方
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingRight
     * @param paddingTop
     * @return
     */
    public static Bitmap drawTextToRightTop(Context context, Bitmap bitmap, String text,
            int size, int color, int paddingRight, int paddingTop) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds, 
                bitmap.getWidth() - bounds.width() - dp2px(context, paddingRight), 
                dp2px(context, paddingTop) + bounds.height());
    }

    /**
     * 繪製文字到左下方
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingLeft
     * @param paddingBottom
     * @return
     */
    public static Bitmap drawTextToLeftBottom(Context context, Bitmap bitmap, String text,
            int size, int color, int paddingLeft, int paddingBottom) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds, 
                dp2px(context, paddingLeft),  
                bitmap.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 繪製文字到中間
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @return
     */
    public static Bitmap drawTextToCenter(Context context, Bitmap bitmap, String text,
            int size, int color) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds, 
                (bitmap.getWidth() - bounds.width()) / 2,  
                (bitmap.getHeight() + bounds.height()) / 2);
    }

    //圖片上繪製文字
    private static Bitmap drawTextToBitmap(Context context, Bitmap bitmap, String text,
            Paint paint, Rect bounds, int paddingLeft, int paddingTop) {
        android.graphics.Bitmap.Config bitmapConfig = bitmap.getConfig();

        paint.setDither(true); // 獲取跟清晰的影象取樣
        paint.setFilterBitmap(true);// 過濾一些
        if (bitmapConfig == null) {
            bitmapConfig = android.graphics.Bitmap.Config.ARGB_8888;
        }
        bitmap = bitmap.copy(bitmapConfig, true);
        Canvas canvas = new Canvas(bitmap);

        canvas.drawText(text, paddingLeft, paddingTop, paint);
        return bitmap;
    }

    /**
     * 縮放圖片
     * @param src
     * @param w
     * @param h
     * @return
     */
    public static Bitmap scaleWithWH(Bitmap src, double w, double h) {
        if (w == 0 || h == 0 || src == null) {
            return src;
        } else {
            // 記錄src的寬高
            int width = src.getWidth();
            int height = src.getHeight();
            // 建立一個matrix容器
            Matrix matrix = new Matrix();
            // 計算縮放比例
            float scaleWidth = (float) (w / width);
            float scaleHeight = (float) (h / height);
            // 開始縮放
            matrix.postScale(scaleWidth, scaleHeight);
            // 建立縮放後的圖片
            return Bitmap.createBitmap(src, 0, 0, width, height, matrix, true);
        }
    }

    /**
     * dip轉pix
     * @param context
     * @param dp
     * @return
     */
    public static int dp2px(Context context, float dp) { 
        final float scale = context.getResources().getDisplayMetrics().density; 
        return (int) (dp * scale + 0.5f); 
    } 
}

使用方法如下：
新增一個佈局，上面是原始圖片，下面是新增水印後的圖片

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/sour_pic_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="原圖" />

    <ImageView 
        android:id="@+id/sour_pic"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scaleType="centerInside"/>

    <TextView
        android:id="@+id/watermark_pic_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="水印" />

    <ImageView 
        android:id="@+id/wartermark_pic"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scaleType="centerInside"/>

</LinearLayout>

(本文出自水寒的CSDN部落格：http://blog.csdn.net/dawanganban）
在Activity中獲取到ImageView物件，並且獲取Bitmap物件，對Bitmap進行canva繪圖，新增水印：

/**
 * 圖片工具類
 * @author 水寒
 * 歡迎訪問水寒的個人部落格：http://www.sunhome.org.cn
 *
 */
public class MainActivity extends Activity {

    private ImageView mSourImage;
    private ImageView mWartermarkImage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initView();
    }

    private void initView(){
        mSourImage = (ImageView) findViewById(R.id.sour_pic);
        mWartermarkImage = (ImageView) findViewById(R.id.wartermark_pic);
        Bitmap sourBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.sour_pic);
        mSourImage.setImageBitmap(sourBitmap);

        Bitmap waterBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.weixin);

        Bitmap watermarkBitmap = ImageUtil.createWaterMaskCenter(sourBitmap, waterBitmap);
        watermarkBitmap = ImageUtil.createWaterMaskLeftBottom(this, watermarkBitmap, waterBitmap, 0, 0);
        watermarkBitmap = ImageUtil.createWaterMaskRightBottom(this, watermarkBitmap, waterBitmap, 0, 0);
        watermarkBitmap = ImageUtil.createWaterMaskLeftTop(this, watermarkBitmap, waterBitmap, 0, 0);
        watermarkBitmap = ImageUtil.createWaterMaskRightTop(this, watermarkBitmap, waterBitmap, 0, 0);

        Bitmap textBitmap = ImageUtil.drawTextToLeftTop(this, watermarkBitmap, "左上角", 16, Color.RED, 0, 0);
        textBitmap = ImageUtil.drawTextToRightBottom(this, textBitmap, "右下角", 16, Color.RED, 0, 0);
        textBitmap = ImageUtil.drawTextToRightTop(this, textBitmap, "右上角", 16, Color.RED, 0, 0);
        textBitmap = ImageUtil.drawTextToLeftBottom(this, textBitmap, "左下角", 16, Color.RED, 0, 0);
        textBitmap = ImageUtil.drawTextToCenter(this, textBitmap, "中間", 16, Color.RED);

        mWartermarkImage.setImageBitmap(textBitmap);
    }
}