1、改变图片颜色

//改变图片颜色
- (UIImage *)imageWithColor:(UIColor *)color
{
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    CGContextRef   context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, self.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGRect   rect = CGRectMake(0, 0, self.size.width, self.size.height);
    CGContextClipToMask(context, rect, self.CGImage);
    [color setFill];
    CGContextFillRect(context, rect);
    UIImage  *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

2、获取image中指定区域的颜色

- (UIColor *)getPixelColorAtLocation:(CGPoint)point {
    UIColor* color = nil;
    CGImageRef inImage = [self CGImage];
    CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
    if (cgctx == NULL) { return nil;  }
    size_t w = CGImageGetWidth(inImage);
    size_t h = CGImageGetHeight(inImage);
    CGRect rect = {{0,0},{w,h}};
    CGContextDrawImage(cgctx, rect, inImage);
    unsigned char* data = CGBitmapContextGetData (cgctx);
    if (data != NULL) {
        @try {
            int offset = 4*((w*round(point.y))+round(point.x));
            int alpha =  data[offset];
            int red = data[offset+1];
            int green = data[offset+2];
            int blue = data[offset+3];
            color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
        }
        @catch (NSException* e) {
            NSLog(@"%@",[e reason]);
        }
        @finally {
        }
    }
    CGContextRelease(cgctx);
    if (data) { free(data); }
    return color;
}
- (CGContextRef)createARGBBitmapContextFromImage:(CGImageRef) inImage {
    CGContextRef    context = NULL;
    CGColorSpaceRef colorSpace;
    void *          bitmapData;
    int             bitmapByteCount;
    int             bitmapBytesPerRow;
    size_t pixelsWide = CGImageGetWidth(inImage);
    size_t pixelsHigh = CGImageGetHeight(inImage);
    bitmapBytesPerRow   = (int)(pixelsWide * 4);
    bitmapByteCount     = (int)(bitmapBytesPerRow * pixelsHigh);
    colorSpace = CGColorSpaceCreateDeviceRGB();
    if (colorSpace == NULL)
    {
        fprintf(stderr, "Error allocating color space\n");
        return NULL;
    }
    bitmapData = malloc( bitmapByteCount );
    if (bitmapData == NULL)
    {
        fprintf (stderr, "Memory not allocated!");
        CGColorSpaceRelease( colorSpace );
        return NULL;
    }
    context = CGBitmapContextCreate (bitmapData,
                                     pixelsWide,
                                     pixelsHigh,
                                     8,      
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedFirst);
    if (context == NULL)
    {
        free (bitmapData);
        fprintf (stderr, "Context not created!");
    }
    CGColorSpaceRelease( colorSpace );
    return context;
}

3、设置图片圆角

//设置图片圆角
- (UIImage *)circleImage {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
    CGContextAddArc(ctx, self.size.width/2.0, self.size.height/2.0, (self.size.width/2.0)>(self.size.height/2.0)?(self.size.height/2.0):(self.size.width/2.0), 0, M_PI*2, 1);
    CGContextClip(ctx);
    [self drawInRect:rect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}