UIImage 读取修改像素颜色

- (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++)

    {

            uint8_t *ptr = (uint8_t*)pCurPtr;

            if (ptr[1] == 255 && ptr[2] == 255 && ptr[3] == 255)

            {

                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;

}

void ProviderReleaseData (void *info, const void *data, size_t size)

{

    free((void*)data);

}