获取黑白 UIImage（非灰度）

Question

我需要从另一个 UIImage （不是灰度）获取纯黑白 UIImage。有人可以帮助我吗？

感谢您的阅读。

已编辑：

这是建议的解决方案。感谢大家。我几乎知道这不是更好的方法，但效果很好。

// 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;
}

编辑1：

为了回应评论，这里有方法bitmapFromImage和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

如果您要寻找的是图像阈值 - 一切都比某个值更明亮，将所有值变成白色，一切都变暗，然后选择该值 - 然后像

Answer 2

这段代码可能有帮助：

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

在 Swift 3 中，我能够通过使用 CIFilters 来实现此效果，首先应用 CIPhotoEffectNoir （使其灰度化），然后应用带有 CIColorControl 滤镜kCIInputContrastKey 输入参数设置为较高值（即 50）。设置 kCIInputBrightnessKey 参数还将调整黑白对比度的强度，负值表示图像较暗，正值表示图像较亮。例如：

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 4

虽然这对于您的目的来说可能有些过分，但我只是在示例应用程序中对来自 iPhone 摄像头的实时视频执行此操作 这里。该应用程序采用颜色和灵敏度，并且可以将在该阈值内的所有像素变为白色，如果不在阈值内则变为透明。为此，我使用 OpenGL ES 2.0 可编程着色器以获得实时响应能力。整个事情在这篇文章这里进行了描述。

再说一次，这对于你想要的东西来说可能有点过分了。对于要转换为黑白的简单 UIImage，您可能可以读取原始像素，迭代它们，并应用与输出最终图像相同的阈值。这不会像着色器方法那么快，但编码会简单得多。

Answer 5

该代码对我来说工作正常，只需要一些调整...这里有一些更改，我通过为 dataBitmap[] 数组 的第 0 个索引赋值来使其正常工作...

     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;
            }
        }

希望它能工作。

Answer 6

这是一个 swift 3 解决方案：

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

这是 Swift 5 的方法，在彩色图标 UIImage 上进行了测试。它将把有颜色的图标变成相同大小的黑白版本：

原始：

转换后：

 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
     }
 }

在 UIButton 上调用它的示例：

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

在此示例中，你可以做更简单的事情：

button.tintColor = .black

但这只是为了展示如果由于某种原因你没有使用按钮，如何取消某些东西的着色。