获得黑白UIImage(非灰度)

Question

我需要从另一个UIImage(不是灰度)获得纯黑白UIImage.有人可以帮帮我吗？

谢谢阅读.

编辑:

这是建议的解决方案.谢谢大家.几乎我知道这不是更好的方法,它工作正常.

// 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:

在回应评论时,这是方法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

此代码可能有所帮助:

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

使用 Swift 3，我能够通过使用 CIFilters 来实现这种效果，首先通过应用CIPhotoEffectNoir（使其成为灰度）然后应用CIColorControl过滤器并将kCIInputContrastKey输入参数设置为高值（即 50）。设置该kCIInputBrightnessKey参数还将调整黑白对比度出现的强度，负值表示较暗的图像，正值表示较亮的图像。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)
    }
}