- (UIImage*)image:(UIImage*)image  fortargetSize: (CGSize)targetSize{

      UIImage*sourceImage = image;

      CGSize imageSize = sourceImage.size;//圖片的size

      CGFloat imageWidth = imageSize.width;//圖片寬度

      CGFloat imageHeight = imageSize.height;//圖片高度

      NSInteger judge;//聲明一個(gè)判斷屬性

       //判斷是否需要調(diào)整尺寸(這個(gè)地方的判斷標(biāo)準(zhǔn)又個(gè)人決定,在此我是判斷高大于寬),因?yàn)閳D片是800*480,所以也可以變成480*800

       if( ( imageHeight - imageWidth)>0) {

               //在這里我將目標(biāo)尺寸修改成480*800

               CGFloat tempW = targetSize.width;

               CGFloat tempH = targetSize.height;

               targetSize.height= tempW;

               targetSize.width= tempH;

        }

         CGFloat targetWidth = targetSize.width;//獲取最終的目標(biāo)寬度尺寸

         CGFloat targetHeight = targetSize.height;//獲取最終的目標(biāo)高度尺寸

         CGFloat scaleFactor ;//先聲明拉伸的系數(shù)

         CGFloat scaledWidth = targetWidth;

         CGFloat scaledHeight = targetHeight;

         CGPoint thumbnailPoint =CGPointMake(0.0,0.0);//這個(gè)是圖片剪切的起點(diǎn)位置

         //第一個(gè)判斷,圖片大小寬跟高都小于目標(biāo)尺寸,直接返回image

         if( imageHeight < targetHeight && imageWidth < targetWidth) {

                return image;

         }

       if ( CGSizeEqualToSize(imageSize, targetSize ) ==NO ) {

              CGFloat widthFactor = targetWidth / imageWidth;  //這里是目標(biāo)寬度除以圖片寬度

               CGFloat heightFactor = targetHeight / imageHeight; //這里是目標(biāo)高度除以圖片高度

               //分四種情況,

               //第一種,widthFactor,heightFactor都小于1,也就是圖片寬度跟高度都比目標(biāo)圖片大,要縮小

        if(widthFactor <1&& heightFactor<1){

               //第一種,需要判斷要縮小哪一個(gè)尺寸,這里看拉伸尺度,我們的scale在小于1的情況下,誰(shuí)越小,等下就用原圖的寬度高度??那一個(gè)系數(shù)(這里不懂的話(huà),代個(gè)數(shù)想一下,例如目標(biāo)800*480  原圖1600*800  系數(shù)就采用寬度系數(shù)widthFactor = 1/2  )

              if(widthFactor > heightFactor){
              judge =1;//右部分空白
               scaleFactor = heightFactor; //修改最后的拉伸系數(shù)是高度系數(shù)(也就是最后要*這個(gè)值)
               }else{
              judge =2;//下部分空白
              scaleFactor = widthFactor;
              }
    }else if(widthFactor >1&& heightFactor <1){

           //第二種,寬度不夠比例,高度縮小一點(diǎn)點(diǎn)(widthFactor大于一,說(shuō)明目標(biāo)寬度比原圖片寬度大,此時(shí)只要拉伸高度系數(shù))

           judge =3;//下部分空白 

            //采用高度拉伸比例

           scaleFactor = imageWidth / targetWidth;// 計(jì)算高度縮小系數(shù) 

}else if(heightFactor >1&& widthFactor <1){

         //第三種,高度不夠比例,寬度縮小一點(diǎn)點(diǎn)(heightFactor大于一,說(shuō)明目標(biāo)高度比原圖片高度大,此時(shí)只要拉伸寬度系數(shù))

         judge =4;//下邊空白

         //采用高度拉伸比例

        scaleFactor = imageHeight / targetWidth;

     }else{

           //第四種,此時(shí)寬度高度都小于目標(biāo)尺寸,不必要處理放大(如果有處理放大的,在這里寫(xiě)).

     }

       scaledWidth= imageWidth * scaleFactor;

       scaledHeight = imageHeight * scaleFactor; 

}

        if(judge ==1){

       //右部分空白

       targetWidth = scaledWidth;//此時(shí)把原來(lái)目標(biāo)剪切的寬度改小,例如原來(lái)可能是800,現(xiàn)在改成780

      }else if(judge ==2){

    //下部分空白

       targetHeight = scaledHeight;

      }else if(judge ==3){

      //第三種,高度不夠比例,寬度縮小一點(diǎn)點(diǎn)

       targetWidth  = scaledWidth; 

      }else{

      //第三種,高度不夠比例,寬度縮小一點(diǎn)點(diǎn)

       targetHeight= scaledHeight;
      }

      UIGraphicsBeginImageContext(targetSize);//開(kāi)始剪切

      CGRect thumbnailRect =CGRectZero;//剪切起點(diǎn)(0,0)

      thumbnailRect.origin= thumbnailPoint;

      thumbnailRect.size.width= scaledWidth;

      thumbnailRect.size.height= scaledHeight;

       [sourceImage drawInRect:thumbnailRect];

       UIImage*newImage =UIGraphicsGetImageFromCurrentImageContext();//截圖拿到圖片

    return newImage;
}