IOS 图片不失真（网络图片，本地图片-）-不涉及分辨率(px➗2 跟本地点做比较)

+ (CGRect )scaleImage:(UIImage *)image toSize:(CGRect)newSize{

    float actualHeight = image.size.height;

    float actualWidth = image.size.width;

    float imgRatio = actualWidth/actualHeight;

    float maxRatio = newSize.size.width/newSize.size.height;

    if(imgRatio!=maxRatio){

        if(imgRatio < maxRatio){

            imgRatio = newSize.size.height/ actualHeight;

            actualWidth = imgRatio * actualWidth;

            actualHeight = newSize.size.height;

        }else{

            imgRatio = newSize.size.width / actualWidth;

            actualHeight = imgRatio * actualHeight;

            actualWidth = newSize.size.width;

        }

    }

    CGRect rect = CGRectMake(0.0,0.0, actualWidth, actualHeight);

    return rect;

}

图片不失真方法：http://superdanny.link/2016/01/28/iOS-Upload-Image/

https://www.jianshu.com/p/76f7eb00ef13

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以下是涉及分辨率，对于图片像素px 确保不失真，方案

    CGFloatw =790;

    CGFloath =200;

    //point  = px / scale

    CGFloatscale = [[UIScreenmainScreen]scale];

    CGFloatnewW = w/scale;

    CGFloatnewH = h/scale;

    if (newW < [UIScreen mainScreen].bounds.size.width) {

        NSLog(@"iphone6+");

        //XR  scale = 2; newW  = 395点  屏幕宽点 = 414点

        //6S+ scale = 3; newW  = 250点  屏幕宽点 = 414点

        //对于分辨率来说, 无法全屏，因为全屏会放大图片，因为图片小

    }else{

        NSLog(@"iphone6以下");

        // 6S scale = 2; newW  = 395点  屏幕宽点 = 375点

        // 对于分辨率来说,可以全屏，因为全屏会缩小图片，因为图片大

    }

iPhone 各屏幕尺寸整理