一、图片压缩

1.1 直接格式转换压缩

UIImagePNGRepresentation(_albumImage);
UIImageJPEGRepresentation(_albumImage, scale);

1.2 Context重新绘制

// 通过上下文对图片压缩处理
- (UIImage*)scaleImage:(UIImage*)image size:(CGSize)imageSize{
   //并把它设置成为当前正在使用的context 
   UIGraphicsBeginImageContext(imageSize);
   //把图片渲染到上下文
   [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
   //从当前context中创建一个改变大小后的图片
   UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
   //使当前的context出堆栈 
   UIGraphicsEndImageContext();
   return newImage;
}

二、图片处理

2.1 图片像素上修改

- (UIImage *)eocFilter{
    
    CGImageRef imageRef = self.image.CGImage;
    size_t width = CGImageGetWidth(imageRef);
    size_t height = CGImageGetHeight(imageRef);
    size_t bits = CGImageGetBitsPerComponent(imageRef);
    size_t bitsPerRow = CGImageGetBytesPerRow(imageRef);
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
    int alphaInfo = CGImageGetAlphaInfo(imageRef);
    
    CGDataProviderRef provideRef = CGImageGetDataProvider(imageRef);
    CFDataRef dataRef = CGDataProviderCopyData(provideRef);
    int lenght = (int)CFDataGetLength(dataRef);
    ///////// 测试 data和const char* 
    NSString *testStr = @"abcdefg123456789";
    NSData *testData = [testStr dataUsingEncoding:NSUTF8StringEncoding];
    const char *testC = [testData bytes];
    for (int i = 0; i < testData.length; i++) {
        printf("i->%d: %c\n", i, testC[i]);
    }
    UInt8 *pixelBuf = (UInt8 *)CFDataGetMutableBytePtr((CFMutableDataRef)dataRef);
    for (int i = 0; i < lenght; i+=4) {
        //////修改原始像素RGB数据
        [self eocImageFilterFormBuf:pixelBuf offset:i];
    }
    
    CGContextRef contextRef = CGBitmapContextCreate(pixelBuf, width, height, bits, bitsPerRow, colorSpace, alphaInfo);
    
    CGImageRef backImageRef = CGBitmapContextCreateImage(contextRef);
    UIImage *backImage = [UIImage imageWithCGImage:backImageRef scale:[UIScreen mainScreen].scale orientation:self.image.imageOrientation];
    
    CFRelease(dataRef);
    CFRelease(contextRef);
    CFRelease(backImageRef);
    return backImage;
}

// 对像素点进行加工
- (void)eocImageFilterFormBuf:(UInt8*)pixelBuf offset:(int)offset{
    
    int offsetR = offset;
    int offsetG = offset + 1;
    int offsetB = offset + 2;
    
    int red   = pixelBuf[offsetR];
    int green = pixelBuf[offsetG];
    int blue  = pixelBuf[offsetB];
    
    int gray = (red + green + blue)/3;
    
    pixelBuf[offsetR] = gray;
    pixelBuf[offsetG] = gray;
    pixelBuf[offsetB] = gray;
}

2.2 Context上修改

1:01 ～ 1:34
3 缩放
3.1 利用系统缩放
3.2 自己实现

• 利用上下文，截取的图片为圆。

- (UIImage*)circleImage:(UIImage*)image{
    // 1 创建上下文
    UIGraphicsBeginImageContext(CGSizeMake(200, 200));
    // 2 获取上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    // 3 操作上下文
    CGRect rect = CGRectMake(0, 0, 200, 200);
    CGContextAddEllipseInRect(context, rect);
    // 截剪上下文为圆形 闭环的
    CGContextClip(context);
    // 4 把image 渲染到相应的上下文中
    [image drawInRect:CGRectMake(0, 0, 200, 200)];
    UIImage *backImage =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return backImage;
}

• 利用上下文将视图变成图片,见图一。

- (void)viewDidLoad {
    [super viewDidLoad];
    UIView * view = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 200)];
    view.backgroundColor = [UIColor purpleColor];
    [self.view addSubview:view];
    
    UIView * subView1 = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 50, 50)];
    subView1.backgroundColor = [UIColor redColor];
    UIView * subView2 = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 50, 50)];
    subView2.backgroundColor = [UIColor greenColor];
    [view addSubview:subView1];
    [view addSubview:subView2];
    
    UIImageView * imgView = [[UIImageView alloc] initWithFrame:CGRectMake(100,300 , 100, 100)];
    imgView.image = [self imgWithView:view];
    imgView.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:imgView];
    
}

- (UIImage *)imgWithView:(UIView *)view{
    //1、开始上下文
    UIGraphicsBeginImageContext(view.frame.size);
    //2、获取上下文
    CGContextRef contextRef = UIGraphicsGetCurrentContext();
    //3、将视图绘制到上下文中
//    [view.layer renderInContext:contextRef];
    [view.layer drawInContext:contextRef];
    //4、获取上下文图片
    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

图一

• 利用上下文修改，将图片进行颜色混合,见图二：

    UIImage * img = [UIImage imageNamed:@"1.jpg"];
    self.imgView1.image = img;
    //1、创建上下文
    UIGraphicsBeginImageContext(img.size);
    //2、获取上下文
    CGContextRef contextRef = UIGraphicsGetCurrentContext();
    NSLog(@"%@",NSStringFromCGSize(img.size));
    //3、将图片绘制到上下文
    [img drawInRect:CGRectMake(0, 0, img.size.width, img.size.height)];
    UIColor *redColor = [UIColor colorWithRed:1 green:0 blue:0 alpha:0.4];
    CGContextSetFillColorWithColor(contextRef, redColor.CGColor);
    //4、将颜色渲染到上下文
    CGContextSetBlendMode(contextRef, kCGBlendModeNormal);
    //5、设置渲染区域
    CGContextFillRect(contextRef, CGRectMake(0, 0, img.size.width, img.size.height));
    //6、生成图片
    CGImageRef imgRef = CGBitmapContextCreateImage(contextRef);
    self.imgView2.image = [UIImage imageWithCGImage:imgRef];
    //7、退出上下文
    UIGraphicsEndImageContext();
    //释放对象
    CFRelease(imgRef);

图二

• 截取图片大小，保证填充UIImageView，并且图片不失真。

- (void)viewDidLoad {
    [super viewDidLoad];
    UIImageView * imgView = [[UIImageView alloc] initWithFrame:CGRectMake(10, 100, 100, 100)];
    UIImage * img = [UIImage imageNamed:@"2"];
    imgView.image = [self ct_imageFromImage:img inRect:imgView.bounds];
    imgView.contentMode = UIViewContentModeScaleAspectFit;
    imgView.backgroundColor = [UIColor redColor];
    [self.view addSubview:imgView];
}

/**
 *  从图片中按指定的位置大小截取图片的一部分
 *
 *  @param image UIImage image 原始的图片
 *  @param rect  CGRect rect 要截取的区域
 *
 *  @return UIImage
 */
- (UIImage *)ct_imageFromImage:(UIImage *)image inRect:(CGRect)rect{
    
    //把像 素rect 转化为 点rect（如无转化则按原图像素取部分图片）
    
    CGFloat x = 0;
    CGFloat y = 0;
    CGFloat width = 0;
    CGFloat height = 0;

    if (rect.size.width / rect.size.height > image.size.width / image.size.height) {
        //截取图片的整个宽度，高度按比例截取
        x = 0;
        width = image.size.width;
        height = rect.size.height / rect.size.width * image.size.width;
        y = (image.size.height - height) / 2.0;
    }else{
        //截取图片的整个高度，宽度按比例截取
        y = 0;
        height = image.size.height;
        width = rect.size.width / rect.size.height * image.size.height;
        x = (image.size.width - width) / 2.0;
    }
    CGRect dianRect = CGRectMake(x, y, width, height);
    
    //截取部分图片并生成新图片
    CGImageRef sourceImageRef = [image CGImage];
    //需要释放改对象
    CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, dianRect);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
    return newImage;
}

2.3 图片缩放

- (void)viewDidLoad {
    [super viewDidLoad];
    self.imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
    self.imgView.image = [UIImage imageNamed:@"1.jpg"];
    [self.scrollView addSubview:self.imgView];
    UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchHandel:)];
    [_scrollView addGestureRecognizer:pinchGesture];
}
- (void)pinchHandel:(UIPinchGestureRecognizer*)gesture{
    NSLog(@"%f", gesture.scale);
    if (gesture.state == UIGestureRecognizerStateBegan) {
        _preScal = 1;
    }
    float scaleF = gesture.scale - _preScal + 1;
    _preScal = gesture.scale;
    self.imgView.transform = CGAffineTransformScale(self.imgView.transform, scaleF, scaleF);
    [_scrollView setContentSize:self.imgView.frame.size];
}