ios 生成图片缩略图

来源：互联网发布：数据库工程师发展怎样编辑：程序博客网时间：2024/04/29 15:48

1.自动缩放到指定大小+ (UIImage *)thumbnailWithImage:(UIImage *)image size:(CGSize)asize{UIImage *newimage;if (nil == image) {newimage = nil;}else{UIGraphicsBeginImageContext(asize);[image drawInRect:CGRectMake(0, 0, asize.width, asize.height)];newimage = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();}return newimage;}2.保持原来的长宽比，生成一个缩略图+ (UIImage *)thumbnailWithImageWithoutScale:(UIImage *)image size:(CGSize)asize{UIImage *newimage;if (nil == image) {newimage = nil;}else{CGSize oldsize = image.size;CGRect rect;if (asize.width/asize.height > oldsize.width/oldsize.height) {rect.size.width = asize.height*oldsize.width/oldsize.height;rect.size.height = asize.height;rect.origin.x = (asize.width - rect.size.width)/2;rect.origin.y = 0;}else{rect.size.width = asize.width;rect.size.height = asize.width*oldsize.height/oldsize.width;rect.origin.x = 0;rect.origin.y = (asize.height - rect.size.height)/2;}UIGraphicsBeginImageContext(asize);CGContextRef context = UIGraphicsGetCurrentContext();CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);UIRectFill(CGRectMake(0, 0, asize.width, asize.height));//clear background[image drawInRect:rect];newimage = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();}return newimage;}

缩略图在使用图像的任何应用程序中都发挥着重要的作用。我们常需要调整图像的大小以将其放入一个较小的空间。

当然，你可以装载一个完全填充有原图的 UIImangeView 并调整其框架的大小，不过将图像重新绘制为占用较小字节

的图像可节省大量内存。重绘缩略图可使用以下3种方法，分别是调整、居中、填充方式。

1、保持图像比例不变的同时调整其大小。需要根据图像的长宽比在其四周留出一些额外区域，用透明像素为图像消关。

2、抽取部分图像来匹配可用空间。并裁剪掉落在像素区外的任何元素。

3、通过匹配可用空间的长度和宽度来填充图像。每个像素都被使用，但是图像将水平或垂直裁剪。

源代码：

//计算适合的大小。并保留其原始图片大小

+ (CGSize) fitSize: (CGSize)thisSize inSize: (CGSize) aSize{    CGFloat scale;    CGSize newsize = thisSize;        if (newsize.height && (newsize.height > aSize.height))    {        scale = aSize.height / newsize.height;        newsize.width *= scale;        newsize.height *= scale;    }        if (newsize.width && (newsize.width >= aSize.width))    {        scale = aSize.width / newsize.width;        newsize.width *= scale;        newsize.height *= scale;    }        return newsize;}／／返回调整的缩略图+ (UIImage *) image: (UIImage *) image fitInSize: (CGSize) viewsize{    // calculate the fitted size    CGSize size = [ImageHelper fitSize:image.size inSize:viewsize];        UIGraphicsBeginImageContext(viewsize);    float dwidth = (viewsize.width - size.width) / 2.0f;    float dheight = (viewsize.height - size.height) / 2.0f;        CGRect rect = CGRectMake(dwidth, dheight, size.width, size.height);    [image drawInRect:rect];        UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();          return newimg;  }／／返回居中的缩略图+ (UIImage *) image: (UIImage *) image centerInSize: (CGSize) viewsize{    CGSize size = image.size;        UIGraphicsBeginImageContext(viewsize);    float dwidth = (viewsize.width - size.width) / 2.0f;    float dheight = (viewsize.height - size.height) / 2.0f;        CGRect rect = CGRectMake(dwidth, dheight, size.width, size.height);    [image drawInRect:rect];        UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();          return newimg;  }／／返回填充的缩略图+ (UIImage *) image: (UIImage *) image fillSize: (CGSize) viewsize{    CGSize size = image.size;        CGFloat scalex = viewsize.width / size.width;    CGFloat scaley = viewsize.height / size.height;    CGFloat scale = MAX(scalex, scaley);            UIGraphicsBeginImageContext(viewsize);        CGFloat width = size.width * scale;    CGFloat height = size.height * scale;        float dwidth = ((viewsize.width - width) / 2.0f);    float dheight = ((viewsize.height - height) / 2.0f);        CGRect rect = CGRectMake(dwidth, dheight, size.width * scale, size.height * scale);    [image drawInRect:rect];        UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();          return newimg;  }

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