我创建了一个绘图程序, 允许用户在其中绘制图像并保存图像, 然后再重新装入, 以便继续绘制。 基本上, 我将绘图作为位图传送到要保存的 JNI 层, 并装入上一张图 。

我使用 OpenCv 写入并读取到 png 文件 。

我注意到一些关于图像转换的怪异之处。 似乎透明性是用 OpenCv 上的黑颜色来计算的。 看一下附着的图像, 包含有转换的线条 。

Correct transparency by passing int array to native code, no color conversion needed:

Darkened transparency by passing Bitmap object to native code, color conversion needed:

可能发生什么情况?

使用本地 Bitmap 保存图像时, < 坚固> 获得像素方法:

if ((error = AndroidBitmap_getInfo(pEnv, jbitmap, &info)) < 0) {
    LOGE("AndroidBitmap_getInfo() failed! error:%d",error);
}

if (0 == error)
{
    if ((error = AndroidBitmap_lockPixels(pEnv, jbitmap, &pixels)) < 0) {
        LOGE("AndroidBitmap_lockPixels() failed ! error=%d", error);
    }
}

if (0 == error)
{
    if (info.format == ANDROID_BITMAP_FORMAT_RGBA_8888)
    {
        LOGI("ANDROID_BITMAP_FORMAT_RGBA_8888");
    }
    else
    {
        LOGI("ANDROID_BITMAP_FORMAT %d",info.format);
    }

    Mat bgra(info.height, info.width, CV_8UC4, pixels);
    Mat image;

    //bgra.copyTo(image);

    // fix pixel order RGBA -> BGRA
    cvtColor(bgra, image, COLOR_RGBA2BGRA);

    vector<int> compression_params;
    compression_params.push_back(CV_IMWRITE_PNG_COMPRESSION);
    compression_params.push_back(3);

    // save image
    if (!imwrite(filePath, image, compression_params))
    {
        LOGE("saveImage() -> Error saving image!");
        error = -7;
    }

    // release locked pixels
    AndroidBitmap_unlockPixels(pEnv, jbitmap);
}

使用本地 Int 像素数组方法保存图像 < 坚固> :

JNIEXPORT void JNICALL Java_com_vblast_smasher_Smasher_saveImageRaw
    (JNIEnv *pEnv, jobject obj, jstring jFilePath, jintArray jbgra, jint options, jint compression)
{
    jint*  _bgra = pEnv->GetIntArrayElements(jbgra, 0);
    const char *filePath = pEnv->GetStringUTFChars(jFilePath, 0);

    if (NULL != filePath)
    {
        Mat image;
        Mat bgra(outputHeight, outputWidth, CV_8UC4, (unsigned char *)_bgra);

        bgra.copyTo(image);

        if (0 == options)
        {
            // replace existing cache value
            mpCache->insert(filePath, image);
        }

        vector<int> compression_params;
        compression_params.push_back(CV_IMWRITE_PNG_COMPRESSION);
        compression_params.push_back(compression);

        // save image
        if (!imwrite(filePath, image))
        {
            LOGE("saveImage() -> Error saving image!");
        }
    }

    pEnv->ReleaseIntArrayElements(jbgra, _bgra, 0);
    pEnv->ReleaseStringUTFChars(jFilePath, filePath);
}

Update 05/25/12:
After a little more research I m finding out that this issue does not happen if I get the int array of pixels from the bitmap and pass that directly to the JNI as opposed to what I do currently which is pass the entire Bitmap to the JNI layer then get the pixels and use cvtColor to convert pixels properly. Am I using the right pixel conversion?