我们在做项目的时候有时候需要给图片添加水印，水寒今天就遇到了这样的问题，所以搞了一个工具类，贴出来大家直接调用就行。

/**

 * 图片工具类

 * @author 水寒

 * 欢迎访问水寒的个人博客：http://www.sunhome.org.cn

 *

 */

public class ImageUtil {

    /**

     * 设置水印图片在左上角

     * @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();

        //创建一个bitmap

        Bitmap newb = Bitmap.createBitmap(width, height, Config.ARGB_8888);// 创建一个新的和SRC长度宽度一样的位图

        //将该图片作为画布

        Canvas canvas = new Canvas(newb);

        //在画布 0，0坐标上开始绘制原始图片

        canvas.drawBitmap(src, 0, 0, null);

        //在画布上绘制水印图片

        canvas.drawBitmap(watermark, paddingLeft, paddingTop, null);

        // 保存

        canvas.save(Canvas.ALL_SAVE_FLAG);

        // 存储

        canvas.restore();

        return newb;

    }

    /**

     * 设置水印图片在右下角

     * @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));

    }

    /**

     * 设置水印图片到右上角

     * @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));

    }

    /**

     * 设置水印图片到左下角

     * @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));

    }

    /**

     * 设置水印图片到中间

     * @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);

    }

    /**

     * 给图片添加文字到左上角

     * @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());

    }

    /**

     * 绘制文字到右下角

     * @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));

    }

    /**

     * 绘制文字到右上方

     * @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());

    }

    /**

     * 绘制文字到左下方

     * @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));

    }

    /**

     * 绘制文字到中间

     * @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);

    }

    //图片上绘制文字

    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); // 获取跟清晰的图像采样

        paint.setFilterBitmap(true);// 过滤一些

        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;

    }

    /**

     * 缩放图片

     * @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 {

            // 记录src的宽高

            int width = src.getWidth();

            int height = src.getHeight();

            // 创建一个matrix容器

            Matrix matrix = new Matrix();

            // 计算缩放比例

            float scaleWidth = (float) (w / width);

            float scaleHeight = (float) (h / height);

            // 开始缩放

            matrix.postScale(scaleWidth, scaleHeight);

            // 创建缩放后的图片

            return Bitmap.createBitmap(src, 0, 0, width, height, matrix, true);

        }

    }

    /**

     * dip转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：

添加一个布局，上面是原始图片，下面是添加水印后的图片

<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="原图" />

    <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博客：http://blog.csdn.net/dawanganban）

在Activity中获取到ImageView对象，并且获取Bitmap对象，对Bitmap进行canva绘图，添加水印：

/**

 * 图片工具类

 * @author 水寒

 * 欢迎访问水寒的个人博客：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, "中间", 16, Color.RED);

        mWartermarkImage.setImageBitmap(textBitmap);

    }

}