图片压缩 UIGraphicsBeginImageContext

+(UIImage *)zipScaleWithImage:(UIImage *)sourceImage{
    //进行图像尺寸的压缩
    CGSize imageSize = sourceImage.size;//取出要压缩的image尺寸
    CGFloat width = imageSize.width;    //图片宽度
    CGFloat height = imageSize.height;  //图片高度
    //1.宽高大于1280(宽高比不按照2来算，按照1来算)
    if (width>1280||height>1280) {
        if (width>height) {
            CGFloat scale = height/width;
            width = 1280;
            height = width*scale;
        }else{
            CGFloat scale = width/height;
            height = 1280;
            width = height*scale;
        }
    //2.宽大于1280高小于1280
    }else if(width>1280||height<1280){
        CGFloat scale = height/width;
        width = 1280;
        height = width*scale;
    //3.宽小于1280高大于1280
    }else if(width<1280||height>1280){
        CGFloat scale = width/height;
        height = 1280;
        width = height*scale;
    //4.宽高都小于1280
    }else{
    }
//进行尺寸重绘
    UIGraphicsBeginImageContext(CGSizeMake(width, height));
    [sourceImage drawInRect:CGRectMake(0,0,width,height)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}