android - native 位图处理和 ALPHA_8

Question

我正在尝试通过 native 函数将图像转换为灰度，使用的一段代码取自 Android in Action(第 2 版；您还可以查看 here)。不幸的是，返回的位图对象最终为空，而不是灰度。

这是我加载 (.png) 图像的方式:

Bitmap original = BitmapFactory.decodeResource(this.getResources(), R.drawable.sample, options);

位图通过了许多安全条件(请在下面检查)。这是 Java 中的 native 函数定义:

public native void convertToGray(Bitmap bitmapIn,Bitmap bitmapOut);

和调用:

// Grayscale bitmap (initially empty)     
Bitmap gray = Bitmap.createBitmap(original.getWidth(),original.getHeight(),Config.ALPHA_8);
// Native function call
convertToGray(original,gray);

函数如下:

JNIEXPORT void JNICALL Java_com_example_Preprocessor_convertToGray(JNIEnv * env, jobject  obj, jobject bitmapcolor,jobject bitmapgray)
{
    AndroidBitmapInfo infocolor;
    AndroidBitmapInfo infogray; 
    void* pixelscolor;
    void* pixelsgray;
    int ret;
    int y;
    int x;    

    LOGI("convertToGray");
    if ((ret = AndroidBitmap_getInfo(env, bitmapcolor, &infocolor)) < 0) {
        LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
        return;
    }    

    if ((ret = AndroidBitmap_getInfo(env, bitmapgray, &infogray)) < 0) {
        LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
        return;
    }

    LOGI("color image :: width is %d; height is %d; stride is %d; format is %d;flags is %d",infocolor.width,infocolor.height,infocolor.stride,infocolor.format,infocolor.flags);
    if (infocolor.format != ANDROID_BITMAP_FORMAT_RGBA_8888) {
        LOGE("Bitmap format is not RGBA_8888 !");
        return;
    }  

    LOGI("gray image :: width is %d; height is %d; stride is %d; format is %d;flags is %d",infogray.width,infogray.height,infogray.stride,infogray.format,infogray.flags);
    if (infogray.format != ANDROID_BITMAP_FORMAT_A_8) {
        LOGE("Bitmap format is not A_8 !");
        return;
    }   

    if ((ret = AndroidBitmap_lockPixels(env, bitmapcolor, &pixelscolor)) < 0) {
        LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    }

    if ((ret = AndroidBitmap_lockPixels(env, bitmapgray, &pixelsgray)) < 0) {
        LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    }

    // modify pixels with image processing algorithm
    for (y=0;y<infocolor.height;y++) {
        argb * line = (argb *) pixelscolor;
        uint8_t * grayline = (uint8_t *) pixelsgray;
        for (x=0;x<infocolor.width;x++) {
            grayline[x] = 0.3 * line[x].red + 0.59 * line[x].green + 0.11*line[x].blue;
        }

        pixelscolor = (char *)pixelscolor + infocolor.stride;
        pixelsgray = (char *) pixelsgray + infogray.stride;
    }

    LOGI("Done! Unlocking pixels...");
    AndroidBitmap_unlockPixels(env, bitmapcolor);
    AndroidBitmap_unlockPixels(env, bitmapgray);
}

颜色位图正确传递，代码的处理部分似乎工作正常，但 bitmapgray 保持为空。我想我在这里遗漏了一些重要的东西。

测试环境:模拟器，v2.2。使用此版本，当从主线程 调用 native 代码时，该函数会起作用。在 2.3 模拟器上，不管调用 C 代码的线程如何，或者位图的加载方式如何，该函数都不起作用。 Android NDK:4b 和 6b。

UPDATE #1: You'll find the complete source code here.

UPDATE #2: RGB_565 instead of ALPHA_8 gives some results. It appears not even setPixels() in Java works for ALPHA_8, and I'm having problems finding info on this config type. Any kind of help would be much appreciated.

Answer 1

我遇到了类似的问题。首先，我为 infogray 使用了 android RGBA_8888 格式而不是 A_8(原始位图是使用 ARGB_8888 格式创建的)。然后，如果您使用 argb 结构而不是 uint_8 作为灰线，则可以像这样填充像素:

for (y = 0; y < infocolor.height; ++y) {
       argb* line = (argb*) pixelscolor;
       argb* grayline = (argb*) pixelsgray;
       for (x = 0; x < infocolor.width; ++x) {         
          grayline[x].red = grayline[x].green = grayline[x].blue = 0.3 * line[x].red + 0.59 * line[x].green + 0.11 * line[x].blue;
       }
       pixelscolor = (char*)pixelscolor + infocolor.stride;
       pixelsgray = (char*)pixelsgray + infogray.stride;
   }