如何使用 CGImageCreateWithMaskingColors 应用多个颜色蒙版？

Question

我对 Objective-C 有点陌生，甚至对 Quartz 2D 编程也比较陌生，所以提前道歉！我有一种方法，我想从 UIImage 中删除一些特定的颜色（不仅仅是一种）。

当我只应用一种颜色蒙版来运行我的项目时，效果非常好。一旦我尝试堆叠它们，“whiteRef”就会出现 NULL。我什至尝试修改我的方法以采用颜色蒙版，然后简单地运行我的方法两次 - 输入不同的颜色蒙版 - 但仍然不行。

非常感谢任何帮助！

- (UIImage *)doctorTheImage:(UIImage *)originalImage
{
    const float brownsMask[6] = {124, 255, 68, 222, 0, 165};
    const float whiteMask[6] = {255, 255,  255, 255, 255, 255};

    UIImageView *imageView = [[UIImageView alloc] initWithImage:originalImage];

    UIGraphicsBeginImageContext(originalImage.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGImageRef brownRef = CGImageCreateWithMaskingColors(imageView.image.CGImage, brownsMask);    
    CGImageRef whiteRef = CGImageCreateWithMaskingColors(brownRef, whiteMask);    
    CGContextDrawImage (context, CGRectMake(0, 0, imageView.image.size.width, imageView.image.size.height), whiteRef);

    CGImageRelease(brownRef);
    CGImageRelease(whiteRef);

    UIImage *doctoredImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    [imageView release];

    return doctoredImage;
}

Answer 1

好吧，我找到了一个很好的解决办法！基本上，我最终是通过 MKMapView 使用图像数据，所以我需要做的就是将图像分解为像素，然后我可以随心所欲地进行处理。就速度而言，它可能不是最佳选择，但确实有效。这是我现在使用的代码示例。

//Split the images into pixels to mess with the image pixel colors individually
size_t bufferLength = gridWidth * gridHeight * 4;
unsigned char *rawData = nil;
rawData = (unsigned char *)[self convertUIImageToBitmapRGBA8:myUIImage];

grid = malloc(sizeof(float)*(bufferLength/4));

NSString *hexColor = nil;

for (int i = 0 ; i < (bufferLength); i=i+4)
{
hexColor = [NSString stringWithFormat: @"%02x%02x%02x", (int)(rawData[i + 0]),(int)(rawData[i + 1]),(int)(rawData[i + 2])];


//mess with colors how you see fit - I just detected certain colors and slapped 
//that into an array of floats which I later put over my mapview much like the 
//hazardmap example from apple.

if ([hexColor isEqualToString:@"ff0299"]) //pink
    value = (float)11;
if ([hexColor isEqualToString:@"9933cc"]) //purple
    value = (float)12;

//etc...

grid[i/4] = value;
}

我还从这里借用了一些方法（即：convertUIImageToBitmapRGBA8）： https://gist.github.com/739132

希望这可以帮助别人！