iOS开发之UIImage等比缩放

前面讲了截取UIImage指定大小区域，很方便的截取

UIImage

。今天要和大家分享的是

UIImage

的缩放。

两种缩放:

缩放到指定大小，也就是指定的

size

.

等比缩放。

缩放到指定大小

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

等比缩放

通过缩放系数

- (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

是缩放系数
。

通过计算得到缩放系数

- (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;

}

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。