参考：https://www.jianshu.com/p/0bd04e3fcb7c

一、图片缩放

image.png

image.png

二、设置图片黑白色

方式一：用GPUImage ，需要构建GPUImage到工程中。

/**
 图像黑白,像黑白漫画
 */
- (void)setupImageViewBlackAndWhiteWithImage:(UIImage *)image {
    GPUImagePicture *imagePicture = [[GPUImagePicture alloc] initWithImage:image];
    GPUImageAverageLuminanceThresholdFilter *averageFliter = [[GPUImageAverageLuminanceThresholdFilter alloc] init];
    averageFliter.thresholdMultiplier = 1.0;
    [imagePicture addTarget:averageFliter];
    [averageFliter useNextFrameForImageCapture];
    [imagePicture processImage];
    _imageView.image = [averageFliter imageFromCurrentFramebuffer];
}

方式二：使用CIImage

/**
 设置黑白色
 */
+ (UIImage *)blackAndWhite:(UIImage *)image
{
    CIImage *beginImage = [CIImage imageWithCGImage:image.CGImage];
    
    CIImage *blackAndWhite = [CIFilter filterWithName:@"CIColorControls" keysAndValues:kCIInputImageKey, beginImage, @"inputBrightness", @0.0, @"inputContrast", @2.5, @"inputSaturation", @0.0, nil].outputImage;
    CIImage *output = [CIFilter filterWithName:@"CIExposureAdjust" keysAndValues:kCIInputImageKey, blackAndWhite, @"inputEV", @1.0, nil].outputImage;
    
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef cgiimage = [context createCGImage:output fromRect:output.extent];
    UIImage *newImage = [UIImage imageWithCGImage:cgiimage scale:image.scale orientation:image.imageOrientation];
    
    CGImageRelease(cgiimage);
    return newImage;
}

三、图片按最大或者最小边缩放图片

//指定缩减的大小
+ (UIImage *)scaleToSize:(CGSize)size image:(UIImage *)image max:(BOOL)max {
    CGSize originImageSize = image.size;
    // 创建一个bitmap的context
    // 并把它设置成为当前正在使用的context
    CGFloat ratio = max ? MAX(size.width / originImageSize.width, size.height / originImageSize.height) :  MIN(size.width / originImageSize.width, size.height / originImageSize.height);
    UIGraphicsBeginImageContext(CGSizeMake(originImageSize.width * ratio, originImageSize.height * ratio));
    // 绘制改变大小的图片
    [image drawInRect:CGRectMake(0,0, originImageSize.width * ratio, originImageSize.height * ratio)];
    // 从当前context中创建一个改变大小后的图片
    UIImage * scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    // 使当前的context出堆栈
    UIGraphicsEndImageContext();
    //返回新的改变大小后的图片
    return scaledImage;
}