UIImage 缩放

两种缩放:

1.缩放到指定大小，也就是指定的`size`.

2.等比缩放。

缩放到指定大小

-(UIImage*)imageCompressWithSimple:(UIImage*)imagescaledToSize:(CGSize)size

{

UIGraphicsBeginImageContext(size);

[imagedrawInRect:CGRectMake(0,0,size.width,size.height)];

UIImage*newImage=UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

returnnewImage;

}

等比缩放

通过缩放系数

-(UIImage*)imageCompressWithSimple:(UIImage*)imagescale:(float)scale

{

CGSizesize=image.size;

CGFloatwidth=size.width;

CGFloatheight=size.height;

CGFloatscaledWidth=width*scale;

CGFloatscaledHeight=height*scale;

UIGraphicsBeginImageContext(size);//thiswillcrop

[imagedrawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];

UIImage*newImage=UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

returnnewImage;

}

`scale`是缩放系数。

通过计算得到缩放系数

-(UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize

{

UIImage*sourceImage=[UIImageimageNamed:@"test.jpg"];

UIImage*newImage=nil;

CGSizeimageSize=sourceImage.size;

CGFloatwidth=imageSize.width;

CGFloatheight=imageSize.height;

CGFloattargetWidth=targetSize.width;

CGFloattargetHeight=targetSize.height;

CGFloatscaleFactor=0.0;

CGFloatscaledWidth=targetWidth;

CGFloatscaledHeight=targetHeight;

CGPointthumbnailPoint=CGPointMake(0.0,0.0);

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

{

CGFloatwidthFactor=targetWidth/width;

CGFloatheightFactor=targetHeight/height;

if(widthFactor>heightFactor)

scaleFactor=widthFactor;//scaletofitheight

else

scaleFactor=heightFactor;//scaletofitwidth

scaledWidth=width*scaleFactor;

scaledHeight=height*scaleFactor;

//centertheimage

if(widthFactor>heightFactor)

{

thumbnailPoint.y=(targetHeight-scaledHeight)*0.5;

}

elseif(widthFactor<heightFactor)

{

thumbnailPoint.x=(targetWidth-scaledWidth)*0.5;

}

}

UIGraphicsBeginImageContext(targetSize);//thiswillcrop

CGRectthumbnailRect=CGRectZero;

thumbnailRect.origin=thumbnailPoint;

thumbnailRect.size.width=scaledWidth;

thumbnailRect.size.height=scaledHeight;

[sourceImagedrawInRect:thumbnailRect];

newImage=UIGraphicsGetImageFromCurrentImageContext();

if(newImage==nil)

NSLog(@"couldnotscaleimage");

//popthecontexttogetbacktothedefault

UIGraphicsEndImageContext();

returnnewImage;

}

很久之前写了一篇文章解决MWPhotoBrowser中的SDWebImage加载大图导致的内存警告问题。这个我记得当时从服务器拿到的照片大概有10几M的样子，加载出来会导致内存警告。所以我当时通过修改SDWebImage源码，就是把下载下来的照片进行缩放，内存就降下来了。一般情况下应该不会加载这么大的照片的，用户要是知道，早把你的APP给删掉了。