获取黑白 UIImage（非灰度）

Question

I need to get a pure black and white UIImage from another UIImage (not grayscale). Anyone can help me?

Thanks for reading.

EDITED:

Here is the proposed solution. Thanks to all. Almost I know that is not the better way to do it, it works fine.

// Gets an pure black and white image from an original image.
- (UIImage *)pureBlackAndWhiteImage:(UIImage *)image {

    unsigned char *dataBitmap = [self bitmapFromImage:image];

    for (int i = 0; i < image.size.width * image.size.height * 4; i += 4) {

        if ((dataBitmap[i + 1] + dataBitmap[i + 2] + dataBitmap[i + 3]) < (255 * 3 / 2)) {
            dataBitmap[i + 1] = 0;
            dataBitmap[i + 2] = 0;
            dataBitmap[i + 3] = 0;
        } else {
            dataBitmap[i + 1] = 255;
            dataBitmap[i + 2] = 255;
            dataBitmap[i + 3] = 255;
        }
    }

    image = [self imageWithBits:dataBitmap withSize:image.size];

    return image;
}

EDITED 1:

In response to comments, Here are methods bitmapFromImage and imageWithBits .

// Retrieves the bits from the context once the image has been drawn.
- (unsigned char *)bitmapFromImage:(UIImage *)image {

    // Creates a bitmap from the given image.
    CGContextRef contex = CreateARGBBitmapContext(image.size);
    if (contex == NULL) {
        return NULL;
    }

    CGRect rect = CGRectMake(0.0f, 0.0f, image.size.width, image.size.height);
    CGContextDrawImage(contex, rect, image.CGImage);
    unsigned char *data = CGBitmapContextGetData(contex);
    CGContextRelease(contex);

    return data;
}

// Fills an image with bits.
- (UIImage *)imageWithBits:(unsigned char *)bits withSize:(CGSize)size {

    // Creates a color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL) {

        fprintf(stderr, "Error allocating color space\n");
        free(bits);
        return nil;
    }

    CGContextRef context = CGBitmapContextCreate (bits, size.width, size.height, 8, size.width * 4, colorSpace, kCGImageAlphaPremultipliedFirst);
    if (context == NULL) {

        fprintf (stderr, "Error. Context not created\n");
        free (bits);
        CGColorSpaceRelease(colorSpace );
        return nil;
    }

    CGColorSpaceRelease(colorSpace );
    CGImageRef ref = CGBitmapContextCreateImage(context);
    free(CGBitmapContextGetData(context));
    CGContextRelease(context);

    UIImage *img = [UIImage imageWithCGImage:ref];
    CFRelease(ref);
    return img;
}

Answer 1

如果您正在寻找的是对图像进行阈值处理 - 比某个值更明亮的一切变为白色，一切变暗变暗，然后选择值 - 那么像GPU图像这样的库将适合您。

Answer 2

This code may help:

for (int i = 0; i < image.size.width * image.size.height * 4; i += 4) {
        if (dataBitmap[i + 0] >= dataBitmap[i + 1] && dataBitmap[i + 0] >= dataBitmap[i + 2]){
        dataBitmap[i + 1] = dataBitmap[i + 0];
        dataBitmap[i + 2] = dataBitmap[i + 0];
    }
    else if (dataBitmap[i + 1] >= dataBitmap[i + 0] && dataBitmap[i + 1] >= dataBitmap[i + 2]) {
        dataBitmap[i + 0] = dataBitmap[i + 1];
        dataBitmap[i + 2] = dataBitmap[i + 1];
    }
    else  {
        dataBitmap[i + 0] = dataBitmap[i + 2];
        dataBitmap[i + 1] = dataBitmap[i + 2];
    }
}

Answer 3

While it may be overkill for your purposes, I do just that for live video from the iPhone camera in my sample application here . That application takes a color and a sensitivity, and can turn all pixels white that are within that threshold and transparent if not. I use OpenGL ES 2.0 programmable shaders for this in order to get realtime responsiveness. The whole thing is described in this post here .

Again, this is probably overkill for what you want. In the case of a simple UIImage that you want to convert to black and white, you can probably read in the raw pixels, iterate through them, and apply the same sort of thresholding I did to output the final image. This won't be as fast as the shader approach, but it will be much simpler to code.

Answer 4

The code worked right for me,just need some tweak ...here are few changes I made to work it properly by assigning value to dataBitmap[] array 's zeroth index...

     for (int i = 0; i < image.size.width * image.size.height * 4; i += 4) {
            //here an index for zeroth element is assigned
            if ((dataBitmap[i + 0]+dataBitmap[i + 1] + dataBitmap[i + 2] + dataBitmap[i + 3]) < (255 * 4 / 2)) {   
         //  multiply four,instead of three              
                dataBitmap[i + 0] = 0;
                dataBitmap[i + 1] = 0;
                dataBitmap[i + 2] = 0;
                dataBitmap[i + 3] = 0;
            } else {
                dataBitmap[i + 0] = 255;
                dataBitmap[i + 1] = 255;
                dataBitmap[i + 2] = 255;
                dataBitmap[i + 3] = 255;
            }
        }

Hope it will work.

Answer 5

With Swift 3, I was able to accomplish this effect by using CIFilters, first by applying CIPhotoEffectNoir (to make it grayscale) and then applying the CIColorControl filter with the kCIInputContrastKey input parameter set to a high value (ie 50). Setting the kCIInputBrightnessKey parameter will also adjust how intense the black-and-white contrast appears, negative for a darker image, and positive for a brighter image. For example:

extension UIImage {
    func toBlackAndWhite() -> UIImage? {
        guard let ciImage = CIImage(image: self) else {
            return nil
        }
        guard let grayImage = CIFilter(name: "CIPhotoEffectNoir", withInputParameters: [kCIInputImageKey: ciImage])?.outputImage else {
            return nil
        }
        let bAndWParams: [String: Any] = [kCIInputImageKey: grayImage,
                                          kCIInputContrastKey: 50.0,
                                          kCIInputBrightnessKey: 10.0]
        guard let bAndWImage = CIFilter(name: "CIColorControls", withInputParameters: bAndWParams)?.outputImage else {
            return nil
        }
        guard let cgImage = CIContext(options: nil).createCGImage(bAndWImage, from: bAndWImage.extent) else {
            return nil
        }
        return UIImage(cgImage: cgImage)
    }
}

Answer 6

Here's a swift 3 solution:

class func pureBlackAndWhiteImage(_ inputImage: UIImage) -> UIImage? {

    guard let inputCGImage = inputImage.cgImage, let context = getImageContext(for: inputCGImage), let data = context.data else { return nil }

    let white = RGBA32(red: 255, green: 255, blue: 255, alpha: 255)
    let black = RGBA32(red: 0, green: 0, blue: 0, alpha: 255)

    let width = Int(inputCGImage.width)
    let height = Int(inputCGImage.height)
    let pixelBuffer = data.bindMemory(to: RGBA32.self, capacity: width * height)

    for x in 0 ..< height {
        for y in 0 ..< width {
            let offset = x * width + y
            if pixelBuffer[offset].red > 0 || pixelBuffer[offset].green > 0 || pixelBuffer[offset].blue > 0 {
                pixelBuffer[offset] = black
            } else {
                pixelBuffer[offset] = white
            }
        }
    }

    let outputCGImage = context.makeImage()
    let outputImage = UIImage(cgImage: outputCGImage!, scale: inputImage.scale, orientation: inputImage.imageOrientation)

    return outputImage
}

class func getImageContext(for inputCGImage: CGImage) ->CGContext? {

    let colorSpace       = CGColorSpaceCreateDeviceRGB()
    let width            = inputCGImage.width
    let height           = inputCGImage.height
    let bytesPerPixel    = 4
    let bitsPerComponent = 8
    let bytesPerRow      = bytesPerPixel * width
    let bitmapInfo       = RGBA32.bitmapInfo

    guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo) else {
        print("unable to create context")
        return nil
    }

    context.setBlendMode(.copy)
    context.draw(inputCGImage, in: CGRect(x: 0, y: 0, width: CGFloat(width), height: CGFloat(height)))

    return context
}

struct RGBA32: Equatable {
    var color: UInt32

    var red: UInt8 {
        return UInt8((color >> 24) & 255)
    }

    var green: UInt8 {
        return UInt8((color >> 16) & 255)
    }

    var blue: UInt8 {
        return UInt8((color >> 8) & 255)
    }

    var alpha: UInt8 {
        return UInt8((color >> 0) & 255)
    }

    init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) {
        color = (UInt32(red) << 24) | (UInt32(green) << 16) | (UInt32(blue) << 8) | (UInt32(alpha) << 0)
    }

    static let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
}

func ==(lhs: RGBA32, rhs: RGBA32) -> Bool {
    return lhs.color == rhs.color
}

Answer 7

Here is a Swift 5 way of doing this, was tested on a colorized icon UIImage. It will take the icon which had color into a black and white version of the same size:

Original:

Transformed:

 extension UIImage {

    func blackAndWhite() -> UIImage? {
        let renderer = UIGraphicsImageRenderer(size: size)
        let result = renderer.image { _ in
            let imageRect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
            draw(in: imageRect, blendMode: .luminosity, alpha: 1.0)
        }
        return result
     }
 }

example of calling it on a UIButton:

button.setTitle("Filters", for: .normal)
button.setImage(icon.blackAndWhite(), for: .normal)

In this example, you can just do the simpler:

button.tintColor = .black

but this was just to show how to un-colorize something if for some reason you were not using a button.