如何在Objective-C中将UIImage转换为黑白UIImage？

Question

I don't want grayscale but rather for the darker colors to turn black and the lighter to turn white. How can I do this? I found something that looks promising here Getting a Black and White UIImage (Not Grayscale) but the line below in the code gives me an error that I can not fix.

CGContextRef contex = CreateARGBBitmapContext(image.size); 

Answer 1

You should used GPUImage .

GPUImageAdaptiveThresholdFilter and GPUImageLuminanceThresholdFilter might be what you're looking for.

Example code:

UIImage *image = [UIImage imageNamed:@"yourimage.png"];
GPUImageLuminanceThresholdFilter *filter = [[GPUImageLuminanceThresholdFilter alloc] init];
UIImage *quickFilteredImage = [filter imageByFilteringImage:image];

Hope this helps!

Answer 2

You can convert your black and white image by using following code.

-(UIImage *)convertOriginalImageToBWImage:(UIImage *)originalImage
{
UIImage *newImage;

CGColorSpaceRef colorSapce = CGColorSpaceCreateDeviceGray();
CGContextRef context = CGBitmapContextCreate(nil, originalImage.size.width * originalImage.scale, originalImage.size.height * originalImage.scale, 8, originalImage.size.width * originalImage.scale, colorSapce, kCGImageAlphaNone);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextSetShouldAntialias(context, NO);
CGContextDrawImage(context, CGRectMake(0, 0, originalImage.size.width, originalImage.size.height), [originalImage CGImage]);

CGImageRef bwImage = CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSapce);

UIImage *resultImage = [UIImage imageWithCGImage:bwImage];
CGImageRelease(bwImage);

UIGraphicsBeginImageContextWithOptions(originalImage.size, NO, originalImage.scale);
[resultImage drawInRect:CGRectMake(0.0, 0.0, originalImage.size.width, originalImage.size.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();


return newImage;
}

Or else you can use GPUImage framework .

It is a BSD-licensed iOS library that lets you apply GPU-accelerated filters and other effects to images, live camera video, and movies.

GPUImage framework

May be it will help you.

Answer 3

For those interested I created a Swift 3 version of @bHuMiCA solution:

extension UIImage {
    var bwImage: UIImage? {
        guard let cgImage = cgImage,
            let bwContext = bwContext else {
                return nil
        }

        let rect = CGRect(origin: .zero, size: size)
        bwContext.draw(cgImage, in: rect)
        let bwCgImage = bwContext.makeImage()

        return bwCgImage.flatMap { UIImage(cgImage: $0) }
    }

    private var bwContext: CGContext? {
        let bwContext = CGContext(data: nil,
                                  width: Int(size.width * scale),
                                  height: Int(size.height * scale),
                                  bitsPerComponent: 8,
                                  bytesPerRow: Int(size.width * scale),
                                  space: CGColorSpaceCreateDeviceGray(),
                                  bitmapInfo: CGImageAlphaInfo.none.rawValue)

        bwContext?.interpolationQuality = .high
        bwContext?.setShouldAntialias(false)

        return bwContext
    }
}