1. 图片压缩

1.1 直接格式转换(jpg(三个颜色通道,rgb) png(四个颜色通道,rgba) (jpg更轻量)

NSData *pngData = UIImagePNGRepresentation(_albumImage);
NSData *jpgData = UIImageJPEGRepresentation(_albumImage, scale);

将图片压缩到小于指定大小(通常限制在36kb以下)

//利用遍历压缩
while (jpgData.length > 36*1024) {
        scale = -0.1;
        jpgData = UIImageJPEGRepresentation(_albumImage, scale);
        if (scale <= 0.1) {
            break;
        }
    }

1.2 context上修改

// 通过上下文对图片压缩处理
- (UIImage*)scaleImage:(UIImage*)image size:(CGSize)imageSize{
    
    UIGraphicsBeginImageContext(imageSize);
    [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

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2. 图片处理

2.1 图片像素上修改

位图的创建

//1.图片data 2.图片width 3.height
//4.位图的每一个组成部分多少大小 5.每一行多少个字节
//6.图片空间 7图片信息(图片的透明度 )
CGBitmapContextCreate(void * _Nullable data, size_t width, size_t height, size_t bitsPerComponent, size_t bytesPerRow, CGColorSpaceRef _Nullable space, uint32_t bitmapInfo)

#注意的是:用core框架的时候要边写边注意释放!!!
- (UIImage *)cpcFilter{
    //获取图片基本信息
    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);
    
    
    
    //获得CFDataRef
    CGDataProviderRef provideRef = CGImageGetDataProvider(imageRef);
    CFDataRef dataRef = CGDataProviderCopyData(provideRef);
    
    
    //原生的像素长度
    int lenght = (int)CFDataGetLength(dataRef);
    //转换成指针形式
    UInt8 *pixelBuf = (UInt8 *)CFDataGetMutableBytePtr((CFMutableDataRef)dataRef);
    for (int i = 0; i < lenght; i+=4) {//注意:每个像素有4个颜色通道 故i+=4  !!!
        //////修改原始像素RGB数据
        [self cpcImageFilterFormBuf:pixelBuf offset:i];
    }
    
    CGContextRef contextRef = CGBitmapContextCreate(pixelBuf, width, height, bits, bitsPerRow, colorSpace, alphaInfo);
    
    
    
    
    //转换uiimage
    CGImageRef backImageRef = CGBitmapContextCreateImage(contextRef);
    UIImage *backImage = [UIImage imageWithCGImage:backImageRef scale:[UIScreen mainScreen].scale orientation:self.image.imageOrientation];
    
    
    //记得要释放
    CFRelease(dataRef);
    CFRelease(contextRef);
    CFRelease(backImageRef);
    
    return backImage;
    
}

// 这块就是对每个像素点进行加工(可以根据自己需求进行图形运算,可以用第三方)
- (void)cpcImageFilterFormBuf:(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

#圆形图片
- (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
    CGContextSetLineWidth(context, 1);
    CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
    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;
    
}

#截图
- (UIImage*)imageFromView:(UIView*)view{
    
    
    // 1 创建上下文
    UIGraphicsBeginImageContext(view.frame.size);
    // 2 获取上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    // 3 把view 渲染到上下吻
    [view.layer renderInContext:context];
    // 4 把上下文中生成图片
    UIImage *image =  UIGraphicsGetImageFromCurrentImageContext();
    
    # 5 局部截图(本质是截图片的部分)
    image = [self getSubImage:CGRectMake(100, 100, _eocImageV.frame.size.width, _eocImageV.frame.size.height) image:image.CGImage];
    UIGraphicsEndImageContext();
    return image;
   
}



- (UIImage*)getSubImage:(CGRect)rect image:(CGImageRef)cgImage{
    
    CGImageRef imageRef = CGImageCreateWithImageInRect(cgImage, rect);
    UIImage *subImage = [UIImage imageWithCGImage:imageRef];
    return subImage;
    
}

#对图片颜色渲染
- (UIImage*)imageWithColor:(UIColor*)color{
    
    
    UIImage *rendImage = [UIImage imageNamed:@"3.jpg"];
    // 1 创建上下文
    UIGraphicsBeginImageContext(rendImage.size);
    // 2 获取上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    // 3 把图片渲染到上下文
    [rendImage drawInRect:CGRectMake(0, 0, rendImage.size.width, rendImage.size.height)];
    
    UIColor *redColor = [UIColor colorWithRed:1 green:0 blue:0 alpha:0.5];
    CGContextSetFillColorWithColor(context, redColor.CGColor);
    // 3 把颜色渲染到上下文
    CGContextSetBlendMode(context, kCGBlendModeNormal);
    // 4 颜色渲染区域
    CGContextFillRect(context, CGRectMake(0, 0,rendImage.size.width, rendImage.size.height));
    // 5 生成图片
    CGImageRef imageRef =  CGBitmapContextCreateImage(context);
    
    UIImage *redImage = [UIImage imageWithCGImage:imageRef];
    CFRelease(imageRef);
    
    UIGraphicsEndImageContext();

    
    // 裁剪
    return redImage;
    
}

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3. 图片缩放

3.1 利用系统缩放

#放在scrollView上缩放 ,但不大满意
- (void)viewDidLoad {
    [super viewDidLoad];
    self.title = @"缩放";
    
    _scrollview.maximumZoomScale = 5;
    _scrollview.minimumZoomScale = 0.5;
    
    
}
- (UIView*)viewForZoomingInScrollView:(UIScrollView *)scrollView{
    
    return _imageView;
    
}

3.2 自己实现

- (void)viewDidLoad {
    [super viewDidLoad];
    self.title = @"缩放";
    


    
    [self cpcScale];
}

- (void)cpcScale{
    
    //默认会覆盖掉scrollView的系统pinch
    UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchHandel:)];
    [_scrollview addGestureRecognizer:pinchGesture];
    
}

- (void)pinchHandel:(UIPinchGestureRecognizer*)gesture{
    
    NSLog(@"%f", gesture.scale);
    //记得把scale置1
    if (gesture.state == UIGestureRecognizerStateBegan) {
        _preScal = 1;
    }
    float scaleF = gesture.scale - _preScal + 1;
    _preScal = gesture.scale;
    _imageView.transform = CGAffineTransformScale(_imageView.transform, scaleF, scaleF);
    [_scrollview setContentSize:_imageView.frame.size];
 
}