iOS開發之UIImage等比縮放

前面講了截取UIImage指定大小區域，很方便的截取UIImage。今天要和大家分享的是UIImage的縮放。

兩種縮放:

1. 縮放到指定大小，也就是指定的size.
2. 等比縮放。
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縮放到指定大小

- (UIImage*)imageCompressWithSimple:(UIImage*)image scaledToSize:(CGSize)size
{
    UIGraphicsBeginImageContext(size);
    [image drawInRect:CGRectMake(0,0,size.width,size.height)];
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

等比縮放

通過縮放系數

- (UIImage*)imageCompressWithSimple:(UIImage*)image scale:(float)scale
{
    CGSize size = image.size;
    CGFloat width = size.width;
    CGFloat height = size.height;
    CGFloat scaledWidth = width * scale;
    CGFloat scaledHeight = height * scale;
    UIGraphicsBeginImageContext(size); // this will crop
    [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];
    UIImage* newImage= UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

scale是縮放系數 。

通過計算得到縮放系數

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize
{


UIImage *sourceImage = [UIImage imageNamed:@"test.jpg"];
UIImage *newImage = nil;
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

if (CGSizeEqualToSize(imageSize, targetSize) == NO)
{
    CGFloat widthFactor = targetWidth / width;
    CGFloat heightFactor = targetHeight / height;
    if (widthFactor > heightFactor)
        scaleFactor = widthFactor; // scale to fit height
    else
        scaleFactor = heightFactor; // scale to fit width

    scaledWidth= width * scaleFactor;
    scaledHeight = height * scaleFactor;
    // center the image
    if (widthFactor > heightFactor)
    {
        thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
    }
    else if (widthFactor < heightFactor)
    {
        thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
    }
}

UIGraphicsBeginImageContext(targetSize); // this will crop
CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width= scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect:thumbnailRect];
newImage = UIGraphicsGetImageFromCurrentImageContext();

if(newImage == nil)
    NSLog(@"could not scale image");
//pop the context to get back to the default
UIGraphicsEndImageContext();

return newImage;


}</pre> 
很久之前寫了一篇文章解決MWPhotoBrowser中的SDWebImage加載大圖導致的內存警告問題。這個我記得當時從服務器拿到的照片大概有10幾M的樣子，加載出來會導致內存警告。所以我當時通過修改SDWebImage源碼，就是把下載下來的照片進行縮放，內存就降下來了。一般情況下應該不會加載這么大的照片的，用戶要是知道，早把你的APP給刪掉了。 

Posted by 李剛 Jul 29th, 2015 12:01 am ios開發 

來源：剛剛在線（微信：iOSDevTip），歡迎分享本文，轉載請保留出處！ 

原文鏈接：http://www.superqq.com/blog/2015/07/29/uiimage-geometric-zoom/