使UIImageView变为灰色

Question

我正在使用AFNetworking库中的setImageWithUrl功能在表格单元格中设置UImageViews，但是我需要将图像变为灰度...是否有任何方法可以实现这一点。我尝试过几个UIImage灰度转换器，但我猜测它们不起作用是因为我正在设置还未下载完成的东西。

- cannyboy

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像这样尝试一个核心图像滤镜。 - Jesse Gumpo

Answer 1

尝试使用这种方法：

- (UIImage *)convertImageToGrayScale:(UIImage *)image
{
  // Create image rectangle with current image width/height
  CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);

  // Grayscale color space
  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

  // Create bitmap content with current image size and grayscale colorspace
  CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);

  // Draw image into current context, with specified rectangle
  // using previously defined context (with grayscale colorspace)
  CGContextDrawImage(context, imageRect, [image CGImage]);

  // Create bitmap image info from pixel data in current context
  CGImageRef imageRef = CGBitmapContextCreateImage(context);

  // Create a new UIImage object  
  UIImage *newImage = [UIImage imageWithCGImage:imageRef];

  // Release colorspace, context and bitmap information
  CGColorSpaceRelease(colorSpace);
  CGContextRelease(context);
  CFRelease(imageRef);

  // Return the new grayscale image
  return newImage;
}

我在这里找到了它：http://mobiledevelopertips.com/graphics/convert-an-image-uiimage-to-grayscale.html

- pasawaya

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这对我非常有效！我尝试了核心图像滤镜，但在我的集合视图中性能很差。使用这种方法非常快速。干得好！ - Robert Wagstaff

只有在不使用透明度（alpha设置为无）的情况下才能正常工作。 - Olof_t

Answer 2

我从 @Jesse Gumpo 的示例中获取了代码，现在将其转换为接口形式。

@implementation UIImage ( Greyscale )

- (UIImage *)greyscaleImage
{
    CIImage * beginImage = [ self CIImage ] ;
    CIImage * evAdjustedCIImage = nil ;
    {
        CIFilter * filter = [ CIFilter filterWithName:@"CIColorControls" 
                                        keysAndValues:kCIInputImageKey, beginImage
                                            , @"inputBrightness", @0.0
                                            , @"inputContrast", @1.1
                                            , @"inputSaturation", @0.0
                                            , nil ] ;
        evAdjustedCIImage = [ filter outputImage ] ;
    }

    CIImage * resultCIImage = nil ;
    {
        CIFilter * filter = [ CIFilter filterWithName:@"CIExposureAdjust" 
                                        keysAndValues:kCIInputImageKey, evAdjustedCIImage
                                            , @"inputEV", @0.7
                                            , nil ] ;
        resultCIImage = [ filter outputImage ] ;
    }

    CIContext * context = [ CIContext contextWithOptions:nil ] ;
    CGImageRef resultCGImage = [ context createCGImage:resultCIImage 
                                              fromRect:resultCIImage.extent ] ;
    UIImage * result = [ UIImage imageWithCGImage:resultCGImage ] ;
    CGImageRelease( resultCGImage ) ;

    return result;
}

@end

现在你只需要这样做：

UIImage * downloadedImage = ... get from AFNetwork results ... ;
downloadedImage = [ downloadedImage greyscaleImage ] ;

... use 'downloadedImage' ...

- nielsbot

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如果在UIImage上调用它，需要传入源吗？较低级别的函数调用似乎很简单，但是上面的接口需要一个输入参数，这似乎是不必要的。如果仅调用- (UIImage *)greyscaleImage呢？ - Erika Electra

是的——那是个打错字。谢谢。 - nielsbot

Answer 3

这篇帖子有点旧了，但我在搜索中找到了它。在this post中，我指出了Swift中创建灰度图像的两种不同方法，可以考虑图像的alpha和比例，并且可以在imageView中显示。

import CoreImage

extension UIImage
{
    /// Applies grayscale with CIColorControls by settings saturation to 0.0.
    /// - Parameter brightness: Default is 0.0.
    /// - Parameter contrast: Default is 1.0.
    /// - Returns: The grayscale image of self if available.
    func grayscaleImage(brightness: Double = 0.0, contrast: Double = 1.0) -> UIImage?
    {
        if let ciImage = CoreImage.CIImage(image: self, options: nil)
        {
            let paramsColor: [String : AnyObject] = [ kCIInputBrightnessKey: NSNumber(double: brightness),
                                                      kCIInputContrastKey:   NSNumber(double: contrast),
                                                      kCIInputSaturationKey: NSNumber(double: 0.0) ]
            let grayscale = ciImage.imageByApplyingFilter("CIColorControls", withInputParameters: paramsColor)

            let processedCGImage = CIContext().createCGImage(grayscale, fromRect: grayscale.extent)
            return UIImage(CGImage: processedCGImage, scale: self.scale, orientation: self.imageOrientation)
        }
        return nil
    }

    /// Create a grayscale image with alpha channel. Is 5 times faster than grayscaleImage().
    /// - Returns: The grayscale image of self if available.
    func convertToGrayScale() -> UIImage?
    {
        // Create image rectangle with current image width/height * scale
        let pixelSize = CGSize(width: self.size.width * self.scale, height: self.size.height * self.scale)
        let imageRect = CGRect(origin: CGPointZero, size: pixelSize)
        // Grayscale color space
        if let colorSpace: CGColorSpaceRef = CGColorSpaceCreateDeviceGray()
        {
            // Create bitmap content with current image size and grayscale colorspace
            let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.None.rawValue)
            if let context: CGContextRef = CGBitmapContextCreate(nil, Int(pixelSize.width), Int(pixelSize.height), 8, 0, colorSpace, bitmapInfo.rawValue)
            {
                // Draw image into current context, with specified rectangle
                // using previously defined context (with grayscale colorspace)
                CGContextDrawImage(context, imageRect, self.CGImage)
                // Create bitmap image info from pixel data in current context
                if let imageRef: CGImageRef = CGBitmapContextCreateImage(context)
                {
                    let bitmapInfoAlphaOnly = CGBitmapInfo(rawValue: CGImageAlphaInfo.Only.rawValue)
                    if let contextAlpha = CGBitmapContextCreate(nil, Int(pixelSize.width), Int(pixelSize.height), 8, 0, nil, bitmapInfoAlphaOnly.rawValue)
                    {
                        CGContextDrawImage(contextAlpha, imageRect, self.CGImage)
                        if let mask: CGImageRef = CGBitmapContextCreateImage(contextAlpha)
                        {
                            // Create a new UIImage object
                            if let newCGImage = CGImageCreateWithMask(imageRef, mask)
                            {
                                // Return the new grayscale image
                                return UIImage(CGImage: newCGImage, scale: self.scale, orientation: self.imageOrientation)
                            }
                        }
                    }
                }
            }

        }
        // A required variable was unexpected nil
        return nil
    }
}

- FBente

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如果您希望此答案保留在本网站上，您必须在此处详细说明您的帖子。 - Martin

注意，这不适用于Swift 4，并且似乎很多CG ***的东西被苹果无缘无故地删除了。 :/ - Shayne

Answer 4

不要使用uiimageView，而是子类化一个UIView，给它

@property (strong, nonatomic) UIImage *image;

与

@synthesize image = _image;

覆盖setter方法

-(void)setImage:(UIImage *)image{
     _image = [self makeImageBW:image];
     [self setNeedsDisplay];
}

- (UIImage *)makeImageBW:(UIImage *)source
{
    CIImage *beginImage = source.CIImage;
    CIImage *blackAndWhite = [CIFilter filterWithName:@"CIColorControls" keysAndValues:kCIInputImageKey, beginImage, @"inputBrightness", [NSNumber numberWithFloat:0.0], @"inputContrast", [NSNumber numberWithFloat:1.1], @"inputSaturation", [NSNumber numberWithFloat:0.0], nil].outputImage;
    CIImage *output = [CIFilter filterWithName:@"CIExposureAdjust" keysAndValues:kCIInputImageKey, blackAndWhite, @"inputEV", [NSNumber numberWithFloat:0.7], nil].outputImage; 
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef ref = [context createCGImage:output fromRect:output.extent];
    UIImage *newImage = [UIImage imageWithCGImage:ref];
    CGImageRelease(cgiimage);
    return newImage;
}

-(void)drawRect:(CGRect)rect{
     [_image drawInRect:rect];
}

在其他地方，您可以使用NSURLRequest设置图像：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{
      NSData *data = [NSURLConnection sendSynchronousRequest:(NSURLRequest *) returningResponse:nil error:nil];
      if (data){
           UIImage *image = [UIImage imageWithData:data];
           if (image) dispatch_async(dispatch_get_main_queue(),^{
                [view setImage:image];
           });
      }
 });

- Jesse Gumpo

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我认为将其设置为UIView可能无法使用AFNetworking的setImageWithUrl方法..? - cannyboy

我不熟悉AFNetworking，但我添加了代码，使其在没有AF库的情况下也能正常工作。 - Jesse Gumpo

个人而言，我会将其添加为 UIImage 的一个类别：-[UIImage(Greyscale) grayscaleImage]...这样你就不需要子类化任何东西。 - nielsbot

好的，我已经将这个作为下面的答案添加了，这段转换代码是来自于这个答案。 - nielsbot