前言

• 最近做挺多的图片处理，透视、缩放、拼接、裁剪、效果等等，那么今天就先来详细对比一下系统API处理缩放的性能，这样也好方便选择那种更优的方式来处理

PNG	JPG

大致分为以下五种API：

1. UIKit，画布 drawInRect: 和 UIGraphicsGetImageFromCurrentImageContext
2. CoreGraphics / Quartz 2D，位图上下文CGContextScaleCTM 和 CGContextDrawImage
3. ImageIO，创建省略图 CGImageSourceCreateWithData 和 CGImageSourceCreateThumbnailAtIndex
4. CoreImage，滤镜 CILanczosScaleTransform
5. Accelerate，vImage CGBitmapContextCreate 和 CGContextDrawImage

API

/// UIKit方式
- (UIImage*)kj_UIKitChangeImageSize:(CGSize)size;
/// Quartz 2D
- (UIImage*)kj_QuartzChangeImageSize:(CGSize)size;
/// ImageIO
- (UIImage*)kj_ImageIOChangeImageSize:(CGSize)size;
/// CoreImage
- (UIImage*)kj_CoreImageChangeImageSize:(CGSize)size;
/// Accelerate
- (UIImage*)kj_AccelerateChangeImageSize:(CGSize)size;

UIKit

画布的形式，使用临时图形上下文来渲染缩放

- (UIImage*)kj_UIKitChangeImageSize:(CGSize)size{
    UIGraphicsBeginImageContext(size);
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

CoreGraphics / Quartz 2D

绘图引擎，提供低级别、轻量级、高保真度的2D渲染

- (UIImage*)kj_QuartzChangeImageSize:(CGSize)size{
    UIGraphicsBeginImageContext(size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0.0, size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextSetBlendMode(context, kCGBlendModeCopy);
    CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), self.CGImage);
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

ImageIO

使用导入 #import <ImageIO/ImageIO.h>
CGImageSource的键值说明

• kCGImageSourceCreateThumbnailWithTransform - 设置缩略图是否进行Transfrom变换
• kCGImageSourceCreateThumbnailFromImageAlways - 设置是否创建缩略图，无论原图像有没有包含缩略图，默认kCFBooleanFalse
• kCGImageSourceCreateThumbnailFromImageIfAbsent - 设置是否创建缩略图，如果原图像有没有包含缩略图，则创建缩略图，默认kCFBooleanFalse
• kCGImageSourceThumbnailMaxPixelSize - 设置缩略图的最大宽/高尺寸 需要设置为CFNumber值，设置后图片会根据最大宽/高 来等比例缩放图片
• kCGImageSourceShouldCache - 设置是否以解码的方式读取图片数据 默认为kCFBooleanTrue，如果设置为true，在读取数据时就进行解码 如果为false 则在渲染时才进行解码

- (UIImage*)kj_ImageIOChangeImageSize:(CGSize)size{
    NSData *date = UIImagePNGRepresentation(self);
    CGFloat max = size.width;
    if (max < size.height) max = size.height;
    CFDictionaryRef dicOptionsRef = (__bridge CFDictionaryRef) @{(id)kCGImageSourceCreateThumbnailFromImageIfAbsent : @(YES),
                                                                 (id)kCGImageSourceThumbnailMaxPixelSize : @(max),
                                                                 (id)kCGImageSourceShouldCache : @(YES),};
    CGImageSourceRef src = CGImageSourceCreateWithData((__bridge CFDataRef)date, nil);
    CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(src, 0, dicOptionsRef);
    UIImage *newImage = [UIImage imageWithCGImage:imageRef];
    if (imageRef != nil) CFRelease(imageRef);
    CFRelease(src);
    return newImage;
}

CoreImage

滤镜的处理方式，综合对比下来，这种是最差
使用导入 #import <CoreImage/CoreImage.h>

- (UIImage*)kj_CoreImageChangeImageSize:(CGSize)size{
    CIImage *ciImage = [CIImage imageWithCGImage:self.CGImage];
    CGFloat scale = fminf(size.height/self.size.height, size.width/self.size.width);
    NSDictionary *dict = @{kCIInputScaleKey:@(scale),kCIInputAspectRatioKey:@(1.),kCIInputImageKey:ciImage};
    CIFilter *filter = [CIFilter filterWithName:@"CILanczosScaleTransform" withInputParameters:dict];
    CIContext *ciContext = [[CIContext alloc] initWithOptions:@{kCIContextUseSoftwareRenderer : @(NO)}];
    CGImageRef ciImageRef = [ciContext createCGImage:filter.outputImage fromRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = [UIImage imageWithCGImage:ciImageRef];
    return newImage;
}

Accelerate

vImage，使用CPU的矢量处理器处理大图像
使用导入 #import <Accelerate/Accelerate.h>

- (UIImage*)kj_AccelerateChangeImageSize:(CGSize)size{
    const size_t width = size.width, height = size.height;
    const size_t bytesPerRow = width * 4;
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
#if __IPHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_6_1
    int bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast;
#else
    int bitmapInfo = kCGImageAlphaPremultipliedLast;
#endif
    CGContextRef bmContext = CGBitmapContextCreate(NULL, width, height, 8, bytesPerRow, space, bitmapInfo);
    CGColorSpaceRelease(space);
    if (!bmContext) return nil;
    CGContextDrawImage(bmContext, CGRectMake(0, 0, width, height), self.CGImage);
    UInt8 * data = (UInt8*)CGBitmapContextGetData(bmContext);
    if (!data){
        CGContextRelease(bmContext);
        return nil;
    }
    CGImageRef imageRef = CGBitmapContextCreateImage(bmContext);
    UIImage *newImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGContextRelease(bmContext);
    return newImage;
}

测试示例

- (void)viewDidLoad {
    [super viewDidLoad];
    CGFloat x,y;
    CGFloat sp = kAutoW(10);
    CGFloat w = (kScreenW-sp*2)/2.;
    CGFloat h = (kScreenH-4*sp-kSTATUSBAR_NAVIGATION_HEIGHT)/3;
    NSArray *names = @[@"原图",@"UIKit",@"Quartz 2D",@"ImageIO",@"CoreImage",@"Accelerate"];
    UIImage *image = kGetImage(@"xxsf");
    CGSize size = CGSizeMake(image.size.width/4.3, image.size.height/4.3);
    for (int k=0; k<names.count; k++) {
        x = k%2*(w+sp)+sp/2;
        y = k/2*(h+sp)+sp+kSTATUSBAR_NAVIGATION_HEIGHT;
        UILabel *label = [UILabel kj_createLabelWithText:names[k] FontSize:16 TextColor:UIColor.orangeColor];
        label.frame = CGRectMake(x, y, w, 20);
        [self.view addSubview:label];
        UIImageView *imageView = [[UIImageView alloc]initWithFrame:CGRectMake(x, y+25, w, h-25)];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.backgroundColor = [UIColor.orangeColor colorWithAlphaComponent:0.1];
        [self.view addSubview:imageView];
        if (k==0) {
            imageView.image = image;
            NSData *date = UIImagePNGRepresentation(image);
            NSLog(@"OriginalData：%lu", (unsigned long)date.length);
        }else if (k==1) {
            CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
            UIImage *img = [image kj_UIKitChangeImageSize:size];
            NSData *date = UIImagePNGRepresentation(img);
            NSLog(@"UIKitTime：%f，Data：%lu", CFAbsoluteTimeGetCurrent() - start,(unsigned long)date.length);
            imageView.image = img;
        }else if (k==2) {
            CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
            UIImage *img = [image kj_QuartzChangeImageSize:size];
            NSData *date = UIImagePNGRepresentation(img);
            NSLog(@"QuartzTime：%f，Data：%lu", CFAbsoluteTimeGetCurrent() - start,(unsigned long)date.length);
            imageView.image = img;
        }else if (k==3) {
            CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
            UIImage *img = [image kj_ImageIOChangeImageSize:size];
            NSData *date = UIImagePNGRepresentation(img);
            NSLog(@"ImageIOTime：%f，Data：%lu", CFAbsoluteTimeGetCurrent() - start,(unsigned long)date.length);
            imageView.image = img;
        }else if (k==4) {
            CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
            UIImage *img = [image kj_CoreImageChangeImageSize:size];
            NSData *date = UIImagePNGRepresentation(img);
            NSLog(@"CoreImageTime：%f，Data：%lu", CFAbsoluteTimeGetCurrent() - start,(unsigned long)date.length);
            imageView.image = img;
        }else if (k==5) {
            CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
            UIImage *img = [image kj_AccelerateChangeImageSize:size];
            NSData *date = UIImagePNGRepresentation(img);
            NSLog(@"AccelerateTime：%f，Data：%lu", CFAbsoluteTimeGetCurrent() - start,(unsigned long)date.length);
            imageView.image = img;
        }
    }
}

PNG图片耗时对比，等比缩放

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:38
打印信息:OriginalData：466290

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:43
打印信息:UIKitTime：0.009362，Data：36902

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:49
打印信息:QuartzTime：0.009098，Data：36901

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:55
打印信息:ImageIOTime：0.053086，Data：38576

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:61
打印信息:CoreImageTime：0.128086，Data：40243

------- 🎈 给我点赞 🎈 -------
编译时间:14:11:38
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:67
打印信息:AccelerateTime：0.008618，Data：35748

JPG耗时比较

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:38
打印信息:OriginalData：189364

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:43
打印信息:UIKitTime：0.001181，Data：19778

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:49
打印信息:QuartzTime：0.001097，Data：19783

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:55
打印信息:ImageIOTime：0.010663，Data：17099

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:61
打印信息:CoreImageTime：0.020129，Data：21078

------- 🎈 给我点赞 🎈 -------
编译时间:14:08:03
文件名:KJImageCompressVC.m
方法名:-[KJImageCompressVC viewDidLoad]
行号:67
打印信息:AccelerateTime：0.001000，Data：19062

综合耗时比较

类型	UIKit	CoreGraphics	ImageIO	CoreImage	Accelerate
PNG	0.009362	0.009098	0.053086	0.128086	0.008618
JPG	0.001181	0.001097	0.010663	0.020129	0.001000

• 大小比较

类型	原图	UIKit	CoreGraphics	ImageIO	CoreImage	Accelerate
PNG	466290	36902	36901	38576	40243	35748
JPG	189364	19778	19783	17099	21078	19062

总结

1. Accelerate 压缩出来质量最小
2. ImageIO 肉眼感觉清晰度最高
3. ImageIO 和 CoreImage 只能做等比缩放

• 感兴趣的朋友可以换不同尺寸的图片多次测试，这样就可得到每种方式在不同区域的性能对比

备注：本文用到的部分函数方法和Demo，均来自三方库KJCategories

图片缩放性能对比介绍就到此完毕，后面有相关再补充