iOS开发之UIImage等比缩放
jopen
9年前
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。
Posted by 李刚 Jul 29th, 2015 12:01 am ios开发
来源：刚刚在线（微信：iOSDevTip），欢迎分享本文，转载请保留出处！
原文链接：http://www.superqq.com/blog/2015/07/29/uiimage-geometric-zoom/