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,其中有一个用户拍摄的照片,但我没有任何关于转换图像颜色的想法.

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

我怎样才能做到这一点？

Answer 1

- (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; 
}

Answer 2

从ciimage标签来看,也许OP正在思考(正确地)Core Image会提供一种快速简便的方法吗？

这就是ObjC:

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

和斯威夫特:

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

CIColorControls只是可以将图像转换为灰度的几个内置核心图像滤镜之一.CIPhotoEffectMono,CIPhotoEffectNoir和CIPhotoEffectTonal是不同的色调映射预设(每个都不带参数),您可以使用CIColorMap等过滤器进行自己的色调映射.

与涉及创建和绘制自己的替代方案不同CGBitmapContext,它们保留原始图像的大小/比例和alpha而无需额外的工作.

Answer 3

虽然PiratM的解决方案有效,但您失去了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;
}

Answer 4

考虑到alpha通道,@ rickster的版本看起来很好.但是没有.AspectFit或Fill contentMode的UIImageView无法显示它.因此必须使用CGImage创建UIImage.此版本实现为Swift UIImage扩展,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
    }
}

更长但更快的方式是修改版本的@ChrisStillwells答案.考虑到Swift中的alpha通道和当前比例,实现为UIImage扩展:

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
    }
}

Answer 5

在 Swift 5 中？使用 CoreImage 做图像过滤，

谢谢@rickster

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
        }
    }
}