UIImage+grayColor.h#import 
     
      @interface UIImage (grayColor)+ (UIImage *)grayImage:(UIImage *)sourceImage;@endUIImage+grayColor.m#import "UIImage+grayColor.h"@implementation UIImage (grayColor)+ (UIImage *)grayImage:(UIImage *)sourceImage{    int bitmapInfo = kCGImageAlphaNone;    int width = sourceImage.size.width;    int height = sourceImage.size.height;    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();    CGContextRef context = CGBitmapContextCreate (nil,                                                  width,                                                  height,                                                  8,      // bits per component                                                  0,                                                  colorSpace,                                                  bitmapInfo);    CGColorSpaceRelease(colorSpace);    if (context == NULL) {        return nil;    }    CGContextDrawImage(context,                       CGRectMake(0, 0, width, height), sourceImage.CGImage);    UIImage *grayImage = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];    CGContextRelease(context);    return grayImage;}@end// 使用 UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 320, self.view.frame.size.height)]; [imageView setImage:[UIImage grayImage:[UIImage imageNamed:@"dark.jpg"]]]; [self.view addSubview:imageView];