[IOS 开发] UIImage改变像素值

- (UIImage*) imageBlackToTransparent:(UIImage*) image
{
    // 分配内存
    const int imageWidth = image.size.width;
    const int imageHeight = image.size.height;
    size_t      bytesPerRow = imageWidth * 4;
    uint32_t* rgbImageBuf = (uint32_t*)malloc(bytesPerRow * imageHeight);

    // 创建context
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbImageBuf, imageWidth, imageHeight, 8, bytesPerRow, colorSpace,kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context, CGRectMake(0, 0, imageWidth, imageHeight), image.CGImage);

    // 遍历像素
    int pixelNum = imageWidth * imageHeight;
    uint32_t* pCurPtr = rgbImageBuf;

    for (int i = 0; i < pixelNum; i++, pCurPtr++)
    {
        if ((*pCurPtr & 0xFFFFFF00) == 0)    // 将黑色变成透明
        {
            uint8_t* ptr = (uint8_t*)pCurPtr;

            ptr[0] = 0;
            ptr[1] = 0;
            ptr[2] = 0;
            ptr[3] = 0;
        }
    }

    // 将内存转成image
    CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, rgbImageBuf, bytesPerRow * imageHeight,ProviderReleaseData);
    CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight, 8, 32, bytesPerRow, colorSpace,kCGImageAlphaLast | kCGBitmapByteOrder32Little, dataProvider,NULL, true, kCGRenderingIntentDefault);

    CGDataProviderRelease(dataProvider);

    UIImage* resultUIImage = [UIImage imageWithCGImage:imageRef];

    // 释放
    CGImageRelease(imageRef);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // free(rgbImageBuf) 创建dataProvider时已提供释放函数，这里不用free
    return resultUIImage;
}

/** 颜色变化 */
void ProviderReleaseData (void *info, const void *data, size_t size)
{
    free((void*)data);
}