反转白到黑的UIImage

Question

我有以下的UIImage：

使用Objective-C，我希望能够反转白色到黑色，反之亦然。

任何帮助，将不胜感激。

Answer 1

- (UIImage *)negativeImage 
{ 
    // get width and height as integers, since we'll be using them as 
    // array subscripts, etc, and this'll save a whole lot of casting 
    CGSize size = self.size; 
    int width = size.width; 
    int height = size.height; 

    // Create a suitable RGB+alpha bitmap context in BGRA colour space 
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB(); 
    unsigned char *memoryPool = (unsigned char *)calloc(width*height*4, 1); 
    CGContextRef context = CGBitmapContextCreate(memoryPool, width, height, 8, width * 4, colourSpace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast); 
    CGColorSpaceRelease(colourSpace); 

    // draw the current image to the newly created context 
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]); 

    // run through every pixel, a scan line at a time... 
    for(int y = 0; y < height; y++) 
    { 
     // get a pointer to the start of this scan line 
     unsigned char *linePointer = &memoryPool[y * width * 4]; 

     // step through the pixels one by one... 
     for(int x = 0; x < width; x++) 
     { 
      // get RGB values. We're dealing with premultiplied alpha 
      // here, so we need to divide by the alpha channel (if it 
      // isn't zero, of course) to get uninflected RGB. We 
      // multiply by 255 to keep precision while still using 
      // integers 
      int r, g, b; 
      if(linePointer[3]) 
      { 
       r = linePointer[0] * 255/linePointer[3]; 
       g = linePointer[1] * 255/linePointer[3]; 
       b = linePointer[2] * 255/linePointer[3]; 
      } 
      else 
       r = g = b = 0; 

      // perform the colour inversion 
      r = 255 - r; 
      g = 255 - g; 
      b = 255 - b; 

      if ((r+g+b)/(3*255) == 0) 
      { 

       linePointer[0] = linePointer[1] = linePointer[2] = 0; 
       linePointer[3] = 0; 
      } 
      else 
      { 
       // multiply by alpha again, divide by 255 to undo the 
       // scaling before, store the new values and advance 
       // the pointer we're reading pixel data from 
       linePointer[0] = r * linePointer[3]/255; 
       linePointer[1] = g * linePointer[3]/255; 
       linePointer[2] = b * linePointer[3]/255; 

      } 
      linePointer += 4; 
     } 
    } 

    // get a CG image from the context, wrap that into a 
    // UIImage 
    CGImageRef cgImage = CGBitmapContextCreateImage(context); 
    UIImage *returnImage = [UIImage imageWithCGImage:cgImage]; 

    // clean up 
    CGImageRelease(cgImage); 
    CGContextRelease(context); 
    free(memoryPool); 

    // and return 
    return returnImage; 
} 

我在UIImage扩展类中添加了上述方法。

Answer 2

首先，您必须将核心图像框架添加到您的项目中。

项目设置 - >目标 “项目名称” - >生成阶段 - >链接二进制与图书馆 - >添加项目 - > CoreImage.framework

其次，导入核心映像头到你的实现文件。

#import <CoreImage/CoreImage.h> 

初始化一个UIImage对象来存储原始文件。

UIImage *inputImage = [UIImage imageNamed:@"imageNamed"]; 

创建CIFilter来定义您要如何修改原UIImage对象。

CIFilter* filter = [CIFilter filterWithName:@"CIColorInvert"]; 
[filter setDefaults]; 
[filter setValue:inputImage.CIImage forKey:@"inputImage"]; 

创建另一个UIImage对象以保留修改的图像。

UIImage *outputImage = [[UIImage alloc] initWithCIImage:filter.outputImage]; 

Voilà！希望它会有所帮助。

Answer 3

斯威夫特

使用CIContext代替-UIImage:CIImage（见https://stackoverflow.com/a/28386697/218152），和建筑在@wtznc's response，这里是一个自包含IBDesignable：

@IBDesignable 
class InvertImage: UIImageView { 

    @IBInspectable var originalImage:UIImage? = nil 

    @IBInspectable var invert:Bool = false { 
     didSet { 
      var inverted = false 
      if let originalImage = self.originalImage { 
       if(invert) { 
        let image = CIImage(CGImage: originalImage.CGImage!) 
        if let filter = CIFilter(name: "CIColorInvert") { 
         filter.setDefaults() 
         filter.setValue(image, forKey: kCIInputImageKey) 

         let context = CIContext(options: nil) 
         let imageRef = context.createCGImage(filter.outputImage!, fromRect: image.extent) 
         self.image = UIImage(CGImage: imageRef) 
         inverted = true 
        } 
       } 
      } 

      if(!inverted) { 
       self.image = self.originalImage 
      } 
     } 
    } 
} 

要使用它，设置原始图像而不是图片自图片将动态关联：

Answer 4

Swift3

extension UIImage { 
    func invertedImage() -> UIImage? { 
     guard let cgImage = self.cgImage else { return nil } 
     let ciImage = CoreImage.CIImage(cgImage: cgImage) 
     guard let filter = CIFilter(name: "CIColorInvert") else { return nil } 
     filter.setDefaults() 
     filter.setValue(ciImage, forKey: kCIInputImageKey) 
     let context = CIContext(options: nil) 
     guard let outputImage = filter.outputImage else { return nil } 
     guard let outputImageCopy = context.createCGImage(outputImage, from: outputImage.extent) else { return nil } 
     return UIImage(cgImage: outputImageCopy) 
    } 
} 

Answer 5

对于Xamarin C＃（IOS的特定;不是跨平台的解决方案）：

public static UIImage InvertImageColors(UIImage original) 
{ 
    return ApplyFilter(original, new CIColorInvert()); 
} 

public static UIImage ApplyFilter(UIImage original, CIFilter filter) 
{ 
    UIImage result; 
    try { 
     CIImage coreImage = original.CGImage; 
     filter.SetValueForKey(coreImage, CIFilterInputKey.Image); 
     CIImage output = filter.OutputImage; 
     CIContext context = CIContext.FromOptions(null); 
     CGImage cgImage = context.CreateCGImage(output, output.Extent); 
     result = UIImage.FromImage(cgImage); 

    } catch (Exception ex) { 
     // .. Log error here .. 
     result = original; 
    } 

    return result; 
} 

注＃1：改编自别人的答案;我失去了原来的位置。
注意＃2：每行只需一步，故意做到这一点，所以您可以看到中间类型，并轻松适应其他情况。

另请参阅Xamarin docs - CIFilter class