使用Renderscript android从位图中获得红色通道的平均值

Question

我目前在一个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Renderscript有一种快速访问位图像素的方法。然而，直到现在我修改了谷歌开发人员页面的代码，未能做到我想要的，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;
}

所以我在上面尝试做的是将指针sum中的所有红色值加起来在Java代码中:

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
我得到的avg值太小(小于150)，而输入位图是一个完全红色的图像。
我尝试在脚本中简单地增加指针*sum，以检查foEach循环是否每次都访问完全相同的像素数量，并且在每次运行中我得到不同的数字。
如果你能帮助我如何正确地做到这一点，那将是最受欢迎的。

Answer 1

注意:这段代码严格涉及到的主要问题是，如何得到一个信道的平均值。

你想要达到的目的可以这样做:

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rsAtomic*函数是因为，如果你正在处理来自不同线程的全局变量，你必须使用线程安全的操作(例如线程安全)。

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: Android上的并行计算，简单的方法