图片缩放的三个函数

程序中一个界面用到了好多张大图，内存报警告了，所以做了一下图片缩放，在网上找了别人写的代码

//把图片做等比缩放，生成一个新图片

- (UIImage *) imageByScalingProportionallyToSize:(CGSize)targetSize sourceImage:(UIImage *)sourceImage {

    UIGraphicsBeginImageContext(targetSize);
        [sourceImage drawInRect:CGRectMake(0, 0, targetSize.width, targetSize.height)];
        UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return scaledImage;

    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);

    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;
}

 

//把图片按照新大小进行裁剪，生成一个新图片

- (UIImage*) imageByScalingAndCroppingForSize:(CGSize)targetSize image:(UIImage *) sourceImage
{
    //    UIImage *sourceImage = self;
    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;
}

- (UIImage *)generatePhotoThumbnail:(UIImage *)image 
{
    // Create a thumbnail version of the image for the event object.
    CGSize size = image.size;
    CGSize croppedSize;
    CGFloat ratio = 64.0;//这个是设置转换后图片的尺寸大小
    CGFloat offsetX = 0.0;
    CGFloat offsetY = 0.0;
    
    // check the size of the image, we want to make it
// a square with sides the size of the smallest dimension
    if (size.width > size.height) {
        offsetX = (size.height - size.width) / 2;
        croppedSize = CGSizeMake(size.height, size.height);
    } else {
        offsetY = (size.width - size.height) / 2;
        croppedSize = CGSizeMake(size.width, size.width);
    }
    
    // Crop the image before resize
    CGRect clippedRect = CGRectMake(offsetX * -1, offsetY * -1, croppedSize.width, croppedSize.height);
 　　//裁剪图片

　　　　CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], clippedRect);

    // Done cropping
    
// Resize the image
    CGRect rect = CGRectMake(0.0, 0.0, ratio, ratio);
    
    UIGraphicsBeginImageContext(rect.size);
    [[UIImage imageWithCGImage:imageRef] drawInRect:rect];
    UIImage *thumbnail = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    // Done Resizing
    
    return thumbnail;
}

实际应用简化

- (UIImage *)generatePhotoThumbnail:(UIImage *)image
{
    CGRect rect=CGRectMake(0, 0, 60, 78);

　　//裁剪图片
    CGImageRef imageRef=CGImageCreateWithImageInRect([image CGImage], CGRectMake(0, 0, 140, 182));
  
    UIGraphicsBeginImageContext(rect.size);
    [[UIImage imageWithCGImage:imageRef]drawInRect:rect];

　　//如果不裁剪图片可以直接画

    //[image drawInRect:CGRectMake(0, 0, theSize.width, theSize.height)];

    UIImage *thumbnail=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return thumbnail;
}

附：

UIImage类并没有提供缩放图片需要用到的API，是不是觉得很吃惊？没关系，我们自己来添加一个。

 

定义缩放图片的Category

//  UIImage+Scale.h
 
@interface UIImage (scale)
 
-(UIImage*)scaleToSize:(CGSize)size;
 
@end
 
实现这个Category的定义

// UIImage+Scale.m  

#import "UIImage+Scale.h"
 
@implementation UIImage (scale)
 
-(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
  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;
}
 
@end

如何使用

// 创建图片
UIImage *image =[UIImage imageNamed:@"myImage.png"];
 
// 更改图片大小
UIImage *scaledImage =[image scaleToSize:CGSizeMake(25.0f, 35.0f)]