android 照片加水印,Android 实现图片加水印或logo

我们常常会遇到为图像加水印或logo的需求，一般可以通过三方库或者软件实现，但其实加水印非常简单，仅用一个函数即可实现。

实现思路，逐一计算水印和原图重叠部分的像素点的RGBA分量：

float percent = watermarkA / 255.0f

dstR = srcR * (1 – percent) + watermarkR * percent;

dstG = srcG * (1 – percent) + watermarkG * percent;

dstB = srcB * (1 – percent) + watermarkB * percent;

dstA = srcA * (1 – percent) + watermarkA * percent;

JNI实现：

extern “C” JNIEXPORT void JNICALL

Java_com_qxt_watermark_WatermarkUtils_add(JNIEnv *env, jclass clazz, jbyteArray src, jint srcWidth,

jint srcHeight, jbyteArray watermark, jint watermarkWidth, jint watermarkHeight,

jint x, jint y) {

uint8_t *_src = (uint8_t *) env->GetByteArrayElements(src, nullptr);

uint8_t *_watermark = (uint8_t *) env->GetByteArrayElements(watermark, nullptr);

int positionX;

if (x

positionX = 0;

} else if (x > srcWidth – watermarkWidth) {

positionX = srcWidth – watermarkWidth;

} else {

positionX = x;

}

int positionY;

if (y

positionY = 0;

} else if (y > srcHeight – watermarkHeight) {

positionY = srcHeight – watermarkHeight;

} else {

positionY = y;

}

for (int h = 0; h

for (int w = 0; w

/*int srcPosition = ((srcHeight – watermarkHeight + y) * srcWidth

+ srcWidth – watermarkWidth + x) * 4;*/

int srcPosition = ((positionY + h) * srcWidth

+ positionX + w) * 4;

int position = (h * watermarkWidth + w) * 4;

float watermarkAlpha = _watermark[position + 3] / 255.0f;

float dstR = _src[srcPosition] * (1.0f – watermarkAlpha)

+ _watermark[position] * watermarkAlpha;

_src[srcPosition] = (uint8_t) dstR;

float dstG = _src[srcPosition + 1] * (1.0f – watermarkAlpha)

+ _watermark[position + 1] * watermarkAlpha;

_src[srcPosition + 1] = (uint8_t) dstG;

float dstB = _src[srcPosition + 2] * (1.0f – watermarkAlpha)

+ _watermark[position + 2] * watermarkAlpha;

_src[srcPosition + 2] = (uint8_t) dstB;

float dstA = _src[srcPosition + 3] * (1.0f – watermarkAlpha)

+ _watermark[position + 3] * watermarkAlpha;

_src[srcPosition + 3] = (uint8_t) dstA;

}

}

env->ReleaseByteArrayElements(watermark, (jbyte *) _watermark, JNI_ABORT);

env->ReleaseByteArrayElements(src, (jbyte *) _src, 0);

}

java函数及参数说明：

/**

*

* @param image, src image byte array

* @param imageWidth, src image width

* @param imageHeight, src image height

* @param watermark, watermark image byte array

* @param watermarkWidth, watermark image width

* @param watermarkHeight, watermark image height

* @param x, watermark coordinate x, x >= 0 && x

* @param y, watermark coordinate y, y >= 0 && y

*/

public static native void add(byte[] image, int imageWidth, int imageHeight,

byte[] watermark, int watermarkWidth, int watermarkHeight,

int x, int y);

可以通过x， y坐标控制水印或者logo图片的位置，最终实现效果：

watermark.png

以上仅是一个demo，在实际项目中，我们可以结合人脸检测，用类似的方法轻松地实现在相机的预览帧中加个兔子耳朵、络腮胡子之类的效果。

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