按比例缩放,size 是你要把图显示到多大区域

+(UIImage*)imageCompressFitSizeScale:(UIImage*)sourceImage targetSize:(CGSize)size

{

    UIImage*newImage =nil;

    CGSizeimageSize = sourceImage.size;

    CGFloatwidth = imageSize.width;

    CGFloatheight = imageSize.height;

    CGFloattargetWidth = size.width;

    CGFloattargetHeight = size.height;

    CGFloatscaleFactor =0.0;

    CGFloatscaledWidth = targetWidth;

    CGFloatscaledHeight = targetHeight;

    CGPointthumbnailPoint =CGPointMake(0.0,0.0);

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

        CGFloatwidthFactor = targetWidth / width;

        CGFloatheightFactor = targetHeight / height;

        if(widthFactor > heightFactor){

            scaleFactor = widthFactor;

        }

        else{

            scaleFactor = heightFactor;

        }

        scaledWidth = width * scaleFactor;

        scaledHeight = height * scaleFactor;

        if(widthFactor > heightFactor){

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

        }elseif(widthFactor < heightFactor){

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

        }

    }

    UIGraphicsBeginImageContext(size);

    CGRectthumbnailRect =CGRectZero;

    thumbnailRect.origin= thumbnailPoint;

    thumbnailRect.size.width= scaledWidth;

    thumbnailRect.size.height= scaledHeight;

    [sourceImagedrawInRect:thumbnailRect];

    newImage =UIGraphicsGetImageFromCurrentImageContext();

    if(newImage ==nil){

        NSLog(@"scale image fail");

    }

    UIGraphicsEndImageContext();

    returnnewImage;

}

-(UIImage*)scaleToSize:(CGSize)size

{

//创建一个bitmap的context

// 并把它设置成为当前正在使用的context

//Determine whether the screen is retina

if([[UIScreen mainScreen]scale]== 2.0){

UIGraphicsBeginImageContextWithOptions(size,NO,2.0);

}else{

UIGraphicsBeginImageContext(size);

}

// 绘制改变大小的图片

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

// 从当前context中创建一个改变大小后的图片

UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();

//使当前的context出堆栈

UIGraphicsEndImageContext();

// 返回新的改变大小后的图片

return scaledImage;

}