反转UIImage，重置alpha会导致访问崩溃

Question

我正在尝试反转和图像，我也需要重置alpha计数，但是当我尝试这样做时会出现错误的访问错误（在最后一行崩溃）。什么不能访问数据阵列？此方法适用于以前的iOS版本。

CGImageRef img;
img =image.CGImage;

CFDataRef dataref=CopyImagePixels(img);
UInt8 *data=(UInt8 *)CFDataGetBytePtr(dataref);
int length=CFDataGetLength(dataref);


for(int index=0;index<length;index+=4){


    int alphaCount = data[index+0];
    int redCount = data[index+1];
    int greenCount = data[index+2];
    int blueCount = data[index+3];
    int average = (int)roundf(0.2*redCount + 0.71*greenCount+ 0.07*blueCount);


    alphaCount = average;
    if (alphaCount < 0) alphaCount = 0; 
    if (alphaCount>255) alphaCount =255;
    data[index+0] = (Byte) alphaCount;    <-----WHERE IT GIVES EXEC BAD ACCESS

 ....}

Answer 1

原来需要在iOS6中将dataref设置为可变

CFMutableDataRef m_DataRef = CFDataCreateMutableCopy(0, 0, CGDataProviderCopyData(CGImageGetDataProvider(inImage)));