截取UIImage指定大小區域
最近遇到這樣的需求：從服務器獲取到一張照片，只需要顯示他的左半部分，或者中間部分等等。也就是截取UIImage指定大小區域。
UIImage擴展：
我的解決方案是對UIImage進行擴展。通過CGImageRef和CGImage完成截取，調用的方法是：CGImageCreateWithImageInRect。擴展類叫UIImage+Crop，具體代碼如下：
UIImage+Crop.h
#import <UIKit/UIKit.h>typedef NS_ENUM(NSInteger, XYCropImageStyle){ XYCropImageStyleRight =0, // 右半部分 XYCropImageStyleCenter =1, // 中間部分 XYCropImageStyleLeft =2, // 左半部分 XYCropImageStyleRightOneOfThird =3, // 右側三分之一部分 XYCropImageStyleCenterOneOfThird =4, // 中間三分之一部分 XYCropImageStyleLeftOneOfThird =5, // 左側三分之一部分 XYCropImageStyleRightQuarter =6, // 右側四分之一部分 XYCropImageStyleCenterRightQuarter =7, // 中間右側四分之一部分 XYCropImageStyleCenterLeftQuarter =8, // 中間左側四分之一部分 XYCropImageStyleLeftQuarter =9, // 左側四分之一部分};@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;}實際運用：
簡單測試一下，看看有沒有實現我們想要的效果。首先，先加載一個完整的UIImageView。這個應該不難。代碼如下：
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];
運行一下：
要對UIImage進行裁剪，首先導入頭文件：
#import "UIImage+Crop.h"
在上面UIImage *image = [UIImage imageNamed:@"ganggang"];這段代碼之后加上下面這句：
image = [image imageByCroppingWithStyle:XYCropImageStyleLeft];
XYCropImageStyleLeft是截取照片的左半部分。效果如下：
截取成功，還可以截取其他區域的，只需要傳入不同的XYCropImageStyle即可實現。
UIImage等比縮放
前面講了截取UIImage指定大小區域，很方便的截取UIImage。今天要和大家分享的是UIImage的縮放。
兩種縮放:
1.縮放到指定大小
- (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.等比縮放
（1）通過縮放系數：
- (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是縮放系數 。
（2）通過計算得到縮放系數
- (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;}新聞熱點
疑難解答
