灰度图片和灰度颜色（代码里面只是一些相关的方法替换按需选取几个就好）

+ (UIImage *)convertToGrayscale:(UIImage*)sourceImage {
    return [self convertToGrayscale:sourceImage.CGImage scale:sourceImage.scale];
}

+ (UIImage *)convertToGrayscale:(CGImageRef)sourceImage scale:(CGFloat)scale {
    if (!sourceImage) {
        return nil;
    }
    
    UIImage *resultUIImage = nil;
    
    @autoreleasepool {
        int width = (int)CGImageGetWidth(sourceImage);
        int height = (int)CGImageGetHeight(sourceImage);

        // the pixels will be painted to this array
        uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));

        // clear the pixels so any transparency is preserved
        memset(pixels, 0, width * height * sizeof(uint32_t));

        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

        // create a context with RGBA pixels
        CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
                                                     kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);

        // paint the bitmap to our context which will fill in the pixels array
        CGContextDrawImage(context, CGRectMake(0, 0, width, height), sourceImage);

        for(int y = 0; y < height; y++) {
            for(int x = 0; x < width; x++) {
                uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];

                // convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
                uint8_t gray = (uint8_t)round(0.299 * rgbaPixel[1] + 0.587 * rgbaPixel[2] + 0.114 * rgbaPixel[3]);
                // set the pixels to gray
                rgbaPixel[1] = gray;
                rgbaPixel[2] = gray;
                rgbaPixel[3] = gray;
            }
        }

        // create a new CGImageRef from our context with the modified pixels
        CGImageRef image = CGBitmapContextCreateImage(context);

        // we're done with the context, color space, and pixels
        CGContextRelease(context);
        CGColorSpaceRelease(colorSpace);
        free(pixels);
        resultUIImage = [UIImage imageWithCGImage:image
                                                     scale:scale
                                               orientation:UIImageOrientationUp];

        // we're done with image now too
        CGImageRelease(image);
    }

    // make a new UIImage to return
    
    return resultUIImage;
}

@interface CALayer (CustomerColorsLayer)


@end


@implementation CALayer (CustomerColorsLayer)


+ (void)load {
//    [self ms_swizzleMethod:@selector(setContents:) withMethod:@selector(mm_setContents:)];
//    [self ms_swizzleMethod:@selector(drawInContext:) withMethod:@selector(mm_drawInContext:)];
}

- (void)mm_setContents:(id)contents {
    static CFTypeID imageType = 0;
    if (imageType == 0) {
        imageType = CFGetTypeID([UIImage imageWithColor:[UIColor whiteColor]].CGImage);
    }
    if (contents != NULL && CFGetTypeID((__bridge CFTypeRef)(contents)) == imageType) {
        @autoreleasepool {
            UIImage *sourceImage = [UIImage imageWithCGImage:(__bridge CGImageRef _Nonnull)(contents)];
            UIImage *grayImage = [UIImage convertToGrayscale:sourceImage];
            [self mm_setContents:(__bridge id)grayImage.CGImage];
        }
    } else {
        [self mm_setContents:contents];
    }
    
    
}

// 这个方法无效
- (void)mm_drawInContext:(CGContextRef)ctx {
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    CGContextSetFillColorSpace(ctx, colorSpace);
    [self mm_drawInContext:ctx];
    CGColorSpaceRelease(colorSpace);
}

@end

@interface UIImageView (CustomerColorsLayer)

@end

@implementation UIImageView (CustomerColorsLayer)

+ (void)load {
    [self ms_swizzleMethod:@selector(setImage:) withMethod:@selector(mm_setImage:)];
}

- (void)mm_setImage:(UIImage *)image {
    [self mm_setImage:[UIImage convertToGrayscale:image]];
}

@end

// 这个方法一定要有
@interface UIColor (CustomerColorsLayer)

@end


@implementation UIColor (CustomerColorsLayer)

+ (void)load {
    [self ms_swizzleClassMethod:@selector(colorWithRed:green:blue:alpha:) withMethod:@selector(grayColorWithRed:green:blue:alpha:)];
}

+ (UIColor *)grayColorWithRed:(CGFloat)r green:(CGFloat)g blue:(CGFloat)b alpha:(CGFloat)a {
    CGFloat gray = r * 0.299 +g * 0.587 + b * 0.114;
    UIColor *grayColor = [UIColor grayColorWithRed:gray green:gray blue:gray alpha:a];
    return  grayColor;
}

@end

 图片全部通过SD加载时使用以下方案：

@interface SDImageIOAnimatedCoder (CustomerColorsLayer)

+ (UIImage *)createFrameAtIndex:(NSUInteger)index source:(CGImageSourceRef)source scale:(CGFloat)scale preserveAspectRatio:(BOOL)preserveAspectRatio thumbnailSize:(CGSize)thumbnailSize options:(NSDictionary *)options;

@end

@implementation SDImageIOAnimatedCoder (CustomerColorsLayer)

+ (void)load {
    [self ms_swizzleClassMethod:@selector(createFrameAtIndex:source:scale:preserveAspectRatio:thumbnailSize:options:) withMethod:@selector(mmCreateFrameAtIndex:source:scale:preserveAspectRatio:thumbnailSize:options:)];
}

+ (nullable UIImage *)mmCreateFrameAtIndex:(NSUInteger)index source:(nonnull CGImageSourceRef)source scale:(CGFloat)scale preserveAspectRatio:(BOOL)preserveAspectRatio thumbnailSize:(CGSize)thumbnailSize options:(nullable NSDictionary *)options {
    UIImage *image = [self mmCreateFrameAtIndex:index source:source scale:scale preserveAspectRatio:preserveAspectRatio thumbnailSize:thumbnailSize options:options];
    return [UIImage convertToGrayscale:image];
}

@end

 使用CoreImage框架里面的方法，性能会好一些

+ (UIImage*)updateDataToGrayImage:(UIImage*)sourceImage {
    CIFilter * filter = [CIFilter filterWithName:@"CIColorControls"];
    [filter setValue:[CIImage imageWithCGImage:sourceImage.CGImage] forKey:kCIInputImageKey];
    //饱和度 0---2 默认为1
    [filter setValue:@0 forKey:kCIInputSaturationKey];
    CIImage *inputImage;
    if (sourceImage.CIImage) {
        inputImage = sourceImage.CIImage;
    } else {
        CGImageRef imageRef = sourceImage.CGImage;
        if (!imageRef) {
            return nil;
        }
        inputImage = [CIImage imageWithCGImage:imageRef];
    }
    if (!inputImage) return nil;
    CIContext *context = [CIContext context];
    [filter setValue:inputImage forKey:kCIInputImageKey];
    CIImage *outputImage = filter.outputImage;
    if (!outputImage) return nil;
    CGImageRef imageRef = [context createCGImage:outputImage fromRect:outputImage.extent];
    if (!imageRef) return nil;
    UIImage *image = [UIImage imageWithCGImage:imageRef scale:sourceImage.scale orientation:sourceImage.imageOrientation];
    CGImageRelease(imageRef);
    
    return image;
}