Question

我目前正在一个Android应用程序中工作，我需要计算位图中红色通道的平均值，我刚刚发现了一个快速访问位图像素的Renderscript。但是直到现在我修改了谷歌开发者页面的代码并且未能想要我想要的，这是我的代码：

Sript：

int *sum;

uchar4 __attribute__ ((kernel)) invert(uchar4 in, uint32_t x, uint32_t y){
uchar4 out = in;
sum[0] += in.r;
out.r = 255 - in.r; 
out.g = 255 - in.g;
out.b = 255 - in.b;
return out;
}

所以我上面尝试做的是在指针“sum”和java代码中总结所有红色值：

int [] sum = new int[2];
Allocation data = Allocation.createSized(rs, Elelement.I32(rs), sum.length, Allocation.USAGE_SCRIPT);
data.copy1DRangeFrom(0, sum.length, sum);

Bitmap output = Bitmap.createBitmap(input.getWith(), input.getHeight(), input.getConfig);
Allocation in = Allocation.createFromBitmap(rs, input);
Allocation out = Allocation.createFromBitmap(rs, output);

ScriptC_root root = new ScriptC_root(rs);
root.bind_sum(sum);
root.forEach_invert(in, out);
out.copyTo(output);
data.copyTo(sum); //Here is where i am trying to geck the sum

//so i try to compute the average 
float avg = sum[0] / input.getWidth() * input.getHeight();

对于位图反转操作，我得到了完全预期的结果
我在avg得到的值太小（低于150），而输入的位图是一个完全红色的图像我试着简单地在脚本中增加指针* sum来检查foEach循环是否每次都访问完全相同数量的像素，并且在每次运行中我得到不同的数字。
关于如何正确地做到这一点的帮助将是最受欢迎的。

Answer 1

注意：此代码与主要问题严格相关，如何获取频道的平均值。

您希望以这种方式实现目标：

1）RenderScript

#pragma rs java_package_name(net.hydex11.channelaverageexample)
#pragma rs_fp_relaxed
#pragma version(1)

// Use two global counters
static int totalSum = 0;
static int counter = 0;

// One kernel just sums up the channel red value and increments 
// the global counter by 1 for each pixel
void __attribute__((kernel)) addRedChannel(uchar4 in){

 rsAtomicAdd(&totalSum, in.r);
 rsAtomicInc(&counter);

}

// This kernel places, inside the output allocation, the average
int __attribute__((kernel)) getTotalSum(int x){
    return totalSum/counter;
}

void resetCounters(){

    totalSum = 0;
    counter = 0;

}

注意：我使用了rsAtomic*函数，因为如果您正在处理来自不同线程的全局变量，则必须使用线程安全操作（例如Thread safety ）。

2）Java端

private void example() {

    RenderScript mRS = RenderScript.create(this);

    // Loads example image
    Bitmap inputImage = BitmapFactory.decodeResource(getResources(), R.drawable.houseimage);
    Allocation inputAllocation = Allocation.createFromBitmap(mRS, inputImage);

    // Allocation where to store the sum result (for output purposes)
    Allocation sumAllocation = Allocation.createSized(mRS, Element.I32(mRS), 1);

    // Init script
    ScriptC_average scriptC_average = new ScriptC_average(mRS);

    // If you have a cycle, you have to reset the counters on each cycle
    //scriptC_average.invoke_resetCounters();

    // 1. Execute sum kernel
    scriptC_average.forEach_addRedChannel(inputAllocation);

    // 2. Execute a kernel that copies the sum into an output allocation
    scriptC_average.forEach_getTotalSum(sumAllocation);

    int sumArray[] = new int[1];
    sumAllocation.copyTo(sumArray);

    // E.g. simple output can be 66
    Log.d("AverageExample", String.format("The average of red channel is %d", sumArray[0]));

}

参考：RenderScript: parallel computing on Android, the easy way

使用Renderscript android从位图中获取红色通道的平均值

1 个答案: