iOS 图片压缩UIImage方法扩展

淡淡的烟草味﹌ 2022-08-21 01:26 309阅读 0赞

[iOS][]自带的提供了一个API如下

NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);

在Iphone上有两种读取图片数据的简单方法: UIImageJPEGRepresentation和UIImagePNGRepresentation. UIImageJPEGRepresentation函数需要两个参数:图片的引用和压缩系数.而UIImagePNGRepresentation只需要图片引用作为参数.通过在实际使用过程中,比较发现: UIImagePNGRepresentation(UIImage\* image) 要比UIImageJPEGRepresentation(UIImage\* image, 1.0) 返回的图片数据量大很多.譬如,同样是读取摄像头拍摄的同样景色的照片, UIImagePNGRepresentation()返回的数据量大小为199K ,而 UIImageJPEGRepresentation(UIImage\* image, 1.0)返回的数据量大小只为140KB,比前者少了50多KB.如果对图片的清晰度要求不高,还可以通过设置 UIImageJPEGRepresentation函数的第二个参数,大幅度降低图片数据量.譬如,刚才拍摄的图片, 通过调用UIImageJPEGRepresentation(UIImage\* image, 1.0)读取数据时,返回的数据大小为140KB,但更改压缩系数后,通过调用UIImageJPEGRepresentation(UIImage\* image, 0.5)读取数据时,返回的数据大小只有11KB多,大大压缩了图片的数据量 ,而且从视角角度看,图片的质量并没有明显的降低.因此,在读取图片数据内容时,建议优先使用UIImageJPEGRepresentation,并可根据自己的实际使用场景,设置压缩系数,进一步降低图片数据量大小。

UIImage *imageNew = [info objectForKey:@"UIImagePickerControllerOriginalImage"];  
    imageNew = [self imageWithImage:imageNew scaledToSize:CGSizeMake(100, 100)];  
    NSData *imageData = UIImageJPEGRepresentation(imageNew, 0.0001);  
    m_selectImage = [UIImage imageWithData:imageData];

.h具体code

#import <Foundation/Foundation.h>  
    @interface UIImage (UIImageExt)  
    - (UIImage *)scaleToSize:(UIImage *)img size:(CGSize)size;  //图片压缩到指定尺寸
    - (UIImage *)imageByScalingAndCroppingForSize:(CGSize)targetSize;  //压缩到指定尺寸等比例压缩
    @end

.m具体code

#import "UIImageExt.h"  
    @implementation UIImage (UIImageExt)  
      
    - (UIImage *)scaleToSize:(UIImage *)img size:(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  
        [img 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;  
    }  
    - (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize  
    {  
        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;  
    }  
    @end

[iOS]: http://lib.csdn.net/base/ios