将黑白滤镜应用于UIImage

Question

我需要在UIImage上应用黑白滤镜。我有一个视图，其中包含用户拍摄的照片，但我对如何转换图像颜色没有任何想法。

- (void)viewDidLoad {
    [super viewDidLoad];
    self.navigationItem.title = NSLocalizedString(@"#Paint!", nil);
    imageView.image = image;
}

我该如何做到这一点？

- user3422862

Answer 1

Objective C

- (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; 
}

迅捷

func convertToGrayScale(image: UIImage) -> UIImage {

    // Create image rectangle with current image width/height
    let imageRect:CGRect = CGRect(x:0, y:0, width:image.size.width, height: image.size.height)

    // Grayscale color space
    let colorSpace = CGColorSpaceCreateDeviceGray()
    let width = image.size.width
    let height = image.size.height

    // Create bitmap content with current image size and grayscale colorspace
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

    // Draw image into current context, with specified rectangle
    // using previously defined context (with grayscale colorspace)
    let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
    context?.draw(image.cgImage!, in: imageRect)
    let imageRef = context!.makeImage()

    // Create a new UIImage object
    let newImage = UIImage(cgImage: imageRef!)

    return newImage
}

- MCMatan

---

有什么想法可以保持透明度不变吗？ - Antzi

@Antzi 将 kCGImageAlphaNone 更改为 kCGImageAlphaPremultipliedLast（或您需要的任何内容） - xaphod

它将背景变成黑色！ - Mahdi Moqadasi

Answer 2

根据ciimage标签，也许提问者（正确地）认为Core Image会提供一种快速简便的方法来实现这个功能？

以下是ObjC代码：

- (UIImage *)grayscaleImage:(UIImage *)image {
    CIImage *ciImage = [[CIImage alloc] initWithImage:image];
    CIImage *grayscale = [ciImage imageByApplyingFilter:@"CIColorControls"
        withInputParameters: @{kCIInputSaturationKey : @0.0}];
    return [UIImage imageWithCIImage:grayscale];
}

还有Swift:

func grayscaleImage(image: UIImage) -> UIImage {
    let ciImage = CIImage(image: image)
    let grayscale = ciImage.imageByApplyingFilter("CIColorControls",
        withInputParameters: [ kCIInputSaturationKey: 0.0 ])
    return UIImage(CIImage: grayscale)
}

CIColorControls是Core Image滤镜中的一个，可以将图像转换为灰度。而CIPhotoEffectMono、CIPhotoEffectNoir和CIPhotoEffectTonal则是不同的色调映射预设（每个都不带参数），您也可以使用像CIColorMap这样的滤镜来进行自定义的色调映射。

与涉及创建和绘制自己的CGBitmapContext的替代方法不同，这些滤镜可以在不需要额外工作的情况下保留原始图像的大小/比例和透明度。

- rickster

---

无法在我的代码中使其正常工作。转换后的图像总是空白的。 - John Haager

这种方法还保留了透明度，而被接受的答案则没有。 - Nick

不保留原始尺寸。 - Charlton Provatas

Answer 3

虽然PiratM的解决方案是可行的，但您会丢失alpha通道。要保留alpha通道，您需要执行一些额外的步骤。

+(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);

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

    context = CGBitmapContextCreate(nil,image.size.width, image.size.height, 8, 0, nil, kCGImageAlphaOnly );
    CGContextDrawImage(context, imageRect, [image CGImage]);
    CGImageRef mask = CGBitmapContextCreateImage(context);

    // Create a new UIImage object
    UIImage *newImage = [UIImage imageWithCGImage:CGImageCreateWithMask(imageRef, mask)];
    CGImageRelease(imageRef);
    CGImageRelease(mask);

    // Return the new grayscale image
    return newImage;
}

- Chris Stillwell

---

谢谢，Chris - 这对我很有效！有一个注意点：第二个CGBitmapContextCreate似乎缺少相应的CGContextRelease。在return语句前添加CGContextRelease(context);就可以解决这个问题。 - Mischinab

Answer 4

在Swift 5中，使用CoreImage进行图像滤镜，

感谢@rickster的贡献。

extension UIImage{
    var grayscaled: UIImage?{
        let ciImage = CIImage(image: self)
        let grayscale = ciImage?.applyingFilter("CIColorControls",
                                                parameters: [ kCIInputSaturationKey: 0.0 ])
        if let gray = grayscale{
            return UIImage(ciImage: gray)
        }
        else{
            return nil
        }
    }
}

- dengST30

---

非常高效，比“CIPhotoEffectNoir”滤镜更快。谢谢！ - Pelanes

Answer 5

@rickster的版本在考虑alpha通道的情况下看起来很好。但是，没有使用.AspectFit或Fill contentMode的UIImageView无法显示它。因此，UIImage必须使用CGImage创建。这个版本作为Swift UIImage扩展实现，保持当前比例并提供一些可选的输入参数：

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
    }
}

更长但更快的方法是修改版的@ChrisStillwells答案。这个方法是在Swift中实现的UIImage扩展，考虑了 alpha 通道和当前比例：

extension UIImage
{
    /// 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

---

好的解决方案，但是如果使用if-let嵌套太多会造成代码难以阅读。可以考虑使用guard语句来简化代码。 - rickster

耶稣基督，毁灭金字塔 D: - Arbitur

Answer 6

将@FBente的代码更新至Swift 5，

使用CoreImage进行图像过滤，

extension UIImage
{
    /// Create a grayscale image with alpha channel. Is 5 times faster than grayscaleImage().
    /// - Returns: The grayscale image of self if available.
    var grayScaled: 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: CGPoint.zero, size: pixelSize)
        // Grayscale color space
         let colorSpace: CGColorSpace = CGColorSpaceCreateDeviceGray()

            // Create bitmap content with current image size and grayscale colorspace
        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)
        if let context: CGContext = CGContext(data: nil, width: Int(pixelSize.width), height: Int(pixelSize.height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
            {
                // Draw image into current context, with specified rectangle
                // using previously defined context (with grayscale colorspace)
                guard let cg = self.cgImage else{
                    return nil
                }
                context.draw(cg, in: imageRect)
                // Create bitmap image info from pixel data in current context
                if let imageRef: CGImage = context.makeImage(){
                    let bitmapInfoAlphaOnly = CGBitmapInfo(rawValue: CGImageAlphaInfo.alphaOnly.rawValue)

                    guard let context = CGContext(data: nil, width: Int(pixelSize.width), height: Int(pixelSize.height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfoAlphaOnly.rawValue) else{
                        return nil
                    }
                    context.draw(cg, in: imageRect)
                    if let mask: CGImage = context.makeImage() {
                        // Create a new UIImage object
                        if let newCGImage = imageRef.masking(mask){
                            // Return the new grayscale image
                            return UIImage(cgImage: newCGImage, scale: self.scale, orientation: self.imageOrientation)
                        }
                    }

                }
            }


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

- black_pearl

Answer 7

Swift 3.0版本：

extension UIImage {
    func convertedToGrayImage() -> UIImage? {
        let width = self.size.width
        let height = self.size.height
        let rect = CGRect(x: 0.0, y: 0.0, width: width, height: height)
        let colorSpace = CGColorSpaceCreateDeviceGray()
        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

        guard let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: 8, bytesPerRow: 0, space: colorSpace, bitmapInfo: bitmapInfo.rawValue) else {
            return nil
        }
        guard let cgImage = cgImage else { return nil }

        context.draw(cgImage, in: rect)
        guard let imageRef = context.makeImage() else { return nil }
        let newImage = UIImage(cgImage: imageRef.copy()!)

        return newImage
    }
}

- Anson Yao

---

这会将我的图像逆时针旋转。你知道为什么吗？ - bhakti123

也许你的原始图像有一个方向。尝试复制这个方向。newImage.imageOrientation = self.imageOrientation - Anson Yao

我尝试使用CIFilters和CIContext，但即使对于相对较小的图像，它也需要很长时间。您的答案更快，并且是我最终使用的方法。 - Phontaine Judd

Answer 8

Swift 4 解决方案

extension UIImage {            
    var withGrayscale: UIImage {    
        guard let ciImage = CIImage(image: self, options: nil) else { return self }    
        let paramsColor: [String: AnyObject] = [kCIInputBrightnessKey: NSNumber(value: 0.0), kCIInputContrastKey: NSNumber(value: 1.0), kCIInputSaturationKey: NSNumber(value: 0.0)]
        let grayscale = ciImage.applyingFilter("CIColorControls", parameters: paramsColor)    
        guard let processedCGImage = CIContext().createCGImage(grayscale, from: grayscale.extent) else { return self }
        return UIImage(cgImage: processedCGImage, scale: scale, orientation: imageOrientation)
    }
}

- Charlton Provatas

Answer 9

Swift3 + GPUImage

import GPUImage

extension UIImage {
    func blackWhite() -> UIImage? {
        guard let image: GPUImagePicture = GPUImagePicture(image: self) else {
            print("unable to create GPUImagePicture")
            return nil
        }
        let filter = GPUImageAverageLuminanceThresholdFilter()
        image.addTarget(filter)
        filter.useNextFrameForImageCapture()
        image.processImage()
        guard let processedImage: UIImage = filter.imageFromCurrentFramebuffer(with: UIImageOrientation.up) else {
            print("unable to obtain UIImage from filter")
            return nil
        }
        return processedImage
    }
}

- neoneye

Answer 10

这是 Swift 1.2 版本

/// convert background image to gray scale
///
/// param: flag if true, image will be rendered in grays scale
func convertBackgroundColorToGrayScale(flag: Bool) {
    if flag == true {
        let imageRect = self.myImage.frame

        let colorSpace = CGColorSpaceCreateDeviceGray()
        let width = imageRect.width
        let height = imageRect.height

        let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.None.rawValue)
        var context = CGBitmapContextCreate(nil, Int(width), Int(height), 8, 0, colorSpace, bitmapInfo)
        let image = self.musicBackgroundColor.image!.CGImage

        CGContextDrawImage(context, imageRect, image)
        let imageRef = CGBitmapContextCreateImage(context)

        let newImage = UIImage(CGImage: CGImageCreateCopy(imageRef))

        self.myImage.image = newImage
    } else {
        // do something else
    }
}

- Miralem Cebic

---

这段代码无法编译，它包含了对未声明变量的引用，比如musicBackgroundColor。 - ChucK