在Android中红色和蓝色是互换的

Question

做一个Sylvain Ratabouil Android NDK（第二版）的例子，从相机获得图像预览，并对其进行本地处理，从YUV转换为RGB，并对其应用滤色器。

代码非常简单，问题发生在传递给这个函数的过滤器中：

public native void decode(Bitmap target, byte[] source, int filter);

目标是对ImageView的引用
源是帧预览数据
过滤器是彩色过滤器

decode(mImageRed,   data, 0xFFFF0000);
decode(mImageGreen, data, 0xFF00FF00);
decode(mImageBlue,  data, 0xFF0000FF);

decode(mImageRed,   data, 0xFF0000FF);
decode(mImageGreen, data, 0xFF00FF00);
decode(mImageBlue,  data, 0xFFFF0000);

*为红色图像用0xFFFF0000改变0xFF0000FF滤镜，反之亦然。

在本机部分中，它所做的只是用位运算符和(&)应用筛选器：

bitmapContent[yIndex] &= pFilter;

有人知道颜色交换的时候吗？因为我认为0xFFF0000是红色的，而不是0xFF0000FF。

void JNICALL
decode(JNIEnv *pEnv, jclass pClass, jobject pTarget, jbyteArray pSource, jint pFilter) {

    // Retrieves bitmap information and locks it for drawing.
    AndroidBitmapInfo bitmapInfo;
    uint32_t *bitmapContent;

    if (AndroidBitmap_getInfo(pEnv, pTarget, &bitmapInfo) < 0)
        abort();

    if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888)
        abort();

    if (AndroidBitmap_lockPixels(pEnv, pTarget, (void **) &bitmapContent) < 0)
        abort();

    // Accesses source array data.
    jbyte *source = (*pEnv)->GetPrimitiveArrayCritical(pEnv, pSource, 0);
    if (source == NULL)
        abort();

    int32_t frameSize = bitmapInfo.width * bitmapInfo.height;
    int32_t yIndex, uvIndex, x, y;
    int32_t colorY, colorU, colorV;
    int32_t colorR, colorG, colorB;
    int32_t y1192;

    // Processes each pixel and converts YUV to RGB color.
    // Algorithm originates from the Ketai open source project.
    // See http://ketai.googlecode.com/.
    for (y = 0, yIndex = 0; y < bitmapInfo.height; y++) {
        colorU = 0;
        colorV = 0;
        // Y is divided by 2 because UVs are subsampled vertically.
        // This means that two consecutives iterations refer to the
        // same UV line (e.g when Y=0 and Y=1).
        uvIndex = frameSize + (y >> 1) * bitmapInfo.width;
        for (x = 0; x < bitmapInfo.width; x++, yIndex++) {
            // Retrieves YUV components. UVs are subsampled
            // horizontally too, hence %2 (1 UV for 2 Y).
            colorY = max(toInt(source[yIndex]) - 16, 0);
            if (!(x % 2)) {
                colorV = toInt(source[uvIndex++]) - 128;
                colorU = toInt(source[uvIndex++]) - 128;
            }
            // Computes R, G and B from Y, U and V.
            y1192 = 1192 * colorY;
            colorR = (y1192 + 1634 * colorV);
            colorG = (y1192 - 833 * colorV - 400 * colorU);
            colorB = (y1192 + 2066 * colorU);

            colorR = clamp(colorR, 0, 262143);
            colorG = clamp(colorG, 0, 262143);
            colorB = clamp(colorB, 0, 262143);

            // Combines R, G, B and A into the final pixel color.
            bitmapContent[yIndex] = color(colorR, colorG, colorB);
            bitmapContent[yIndex] &= pFilter;
        }
    }

    (*pEnv)->ReleasePrimitiveArrayCritical(pEnv, pSource, source, 0);
    if (AndroidBitmap_unlockPixels(pEnv, pTarget) < 0)
        abort();
}

mImageR = Bitmap.createBitmap(size.width, size.height, Bitmap.Config.ARGB_8888);
mImageG = Bitmap.createBitmap(size.width, size.height, Bitmap.Config.ARGB_8888);
mImageB = Bitmap.createBitmap(size.width, size.height, Bitmap.Config.ARGB_8888);
mImageViewR.setImageBitmap(mImageR);
mImageViewG.setImageBitmap(mImageG);
mImageViewB.setImageBitmap(mImageB);

Answer 1

您的decode()函数是为NV21视频格式硬编码的，但相机可以为YV12设置。这可能是颜色“交换”的原因。请注意，对于某些分辨率，YV12可以有行填充(NV21保证“完全包装”）。

在一次运行中生成三个平面可能要快得多，但目前还不清楚整数运算是否真的比现代CPU上的浮点运算快。

如果分辨率很高，并且处理时间很重要，可以考虑使用RenderScript。