iOS应用开发中对UIImage进行截取和缩放的方法详解

2020-07-26 03:21:54

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截取UIImage指定大小区域
最近遇到这样的需求：从服务器获取到一张照片，只需要显示他的左半部分，或者中间部分等等。也就是截取UIImage指定大小区域。

UIImage扩展：

我的解决方案是对UIImage进行扩展。通过CGImageRef和CGImage完成截取，调用的方法是：CGImageCreateWithImageInRect。扩展类叫UIImage+Crop，具体代码如下：

UIImage+Crop.h

#import <UIKit/UIKit.h>typedef NS_ENUM(NSInteger, XYCropImageStyle){  XYCropImageStyleRight        =0,   // 右半部分  XYCropImageStyleCenter       =1,   // 中间部分  XYCropImageStyleLeft        =2,   // 左半部分  XYCropImageStyleRightOneOfThird   =3,   // 右侧三分之一部分  XYCropImageStyleCenterOneOfThird  =4,   // 中间三分之一部分  XYCropImageStyleLeftOneOfThird   =5,   // 左侧三分之一部分  XYCropImageStyleRightQuarter    =6,   // 右侧四分之一部分  XYCropImageStyleCenterRightQuarter =7,   // 中间右侧四分之一部分  XYCropImageStyleCenterLeftQuarter  =8,   // 中间左侧四分之一部分  XYCropImageStyleLeftQuarter     =9,   // 左侧四分之一部分};@interface UIImage (Crop)- (UIImage *)imageByCroppingWithStyle:(XYCropImageStyle)style;@endUIImage+Crop.m#import "UIImage+Crop.h"@implementation UIImage (Crop)- (UIImage *)imageByCroppingWithStyle:(XYCropImageStyle)style{  CGRect rect;  switch (style) {    case XYCropImageStyleLeft:      rect = CGRectMake(0, 0, self.size.width/2, self.size.height);      break;    case XYCropImageStyleCenter:      rect = CGRectMake(self.size.width/4, 0, self.size.width/2, self.size.height);      break;    case XYCropImageStyleRight:      rect = CGRectMake(self.size.width/2, 0, self.size.width/2, self.size.height);      break;    case XYCropImageStyleLeftOneOfThird:      rect = CGRectMake(0, 0, self.size.width/3, self.size.height);      break;    case XYCropImageStyleCenterOneOfThird:      rect = CGRectMake(self.size.width/3, 0, self.size.width/3, self.size.height);      break;    case XYCropImageStyleRightOneOfThird:      rect = CGRectMake(self.size.width/3*2, 0, self.size.width/3, self.size.height);      break;    case XYCropImageStyleLeftQuarter:      rect = CGRectMake(0, 0, self.size.width/4, self.size.height);      break;    case XYCropImageStyleCenterLeftQuarter:      rect = CGRectMake(self.size.width/4, 0, self.size.width/4, self.size.height);      break;    case XYCropImageStyleCenterRightQuarter:      rect = CGRectMake(self.size.width/4*2, 0, self.size.width/4, self.size.height);      break;    case XYCropImageStyleRightQuarter:      rect = CGRectMake(self.size.width/4*3, 0, self.size.width/4, self.size.height);      break;    default:      break;  }  CGImageRef imageRef = self.CGImage;  CGImageRef imagePartRef = CGImageCreateWithImageInRect(imageRef, rect);  UIImage *cropImage = [UIImage imageWithCGImage:imagePartRef];  CGImageRelease(imagePartRef);  return cropImage;}

实际运用：

简单测试一下，看看有没有实现我们想要的效果。首先，先加载一个完整的UIImageView。这个应该不难。代码如下：

UIImageView *imgView = [[UIImageView alloc] init];imgView.frame = CGRectMake((SCREEN.width - 226) / 2, 100, 226, 106);UIImage *image = [UIImage imageNamed:@"ganggang"];imgView.image = image;[self.view addSubview:imgView];

运行一下：

201642391121594.png (640×1136)

要对UIImage进行裁剪，首先导入头文件：

#import "UIImage+Crop.h"

在上面UIImage *image = [UIImage imageNamed:@"ganggang"];这段代码之后加上下面这句：

image = [image imageByCroppingWithStyle:XYCropImageStyleLeft];

XYCropImageStyleLeft是截取照片的左半部分。效果如下：

201642391201105.png (640×1136)

截取成功，还可以截取其他区域的，只需要传入不同的XYCropImageStyle即可实现。

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。

1.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;}

2.等比缩放

（1）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。

（2）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;}

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