变更记录

序号 录入时间 录入人 备注
1 2016-01-22 Alfred Jiang -

方案名称

UIImage - 获取 UIImage 大小与压缩 UIImage

关键字

UIImage \ 大小 \ 尺寸 \ 压缩

需求场景

  1. 需要对加载的 UIImage 进行压缩时

参考链接

  1. CSDN - UIImage 图片处理：截图，缩放，设定大小，存储
  2. Stack Overflow - iOS get UIImage memory size

详细内容

获取 UIImage 大小

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UIImage *testImage = [UIImage imageNamed:@"blue2.png"]; //877KB 600*600像素
    
NSUInteger s1 = UIImagePNGRepresentation(testImage).length;         //992400

NSUInteger s2 = UIImageJPEGRepresentation(testImage, 1).length;     //923162

NSUInteger s3  = CGImageGetHeight(testImage.CGImage) * CGImageGetBytesPerRow(testImage.CGImage);    //1440000 = 600 * 600 * 4

//像素尺寸
CGFloat fixelW = CGImageGetWidth(testImage.CGImage);

CGFloat fixelH = CGImageGetHeight(testImage.CGImage);

测试文件大小为 877KB 600*600像素

其中 s1 为保存 PNG 格式文件最大内存占用大小

其中 s2 为保存 JPEG 格式文件最大内存占用大小

其中 s3 为该图片文件当前实际内存占用大小，与像素有关

从测试数据可见实际使用图片所占用内存大小往往大于图片实际大小，所以建议对较大图片进行压缩使用

压缩 UIImage

UIImage+Scale.h

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@interface UIImage (Scale)

//等比率缩放
- (UIImage *)scaleImageToScale:(float)scale;

//自定长宽
- (UIImage*)scaleImageToSize:(CGSize)size;

@end

UIImage+Scale.m

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#import "UIImage+Scale.h"

@implementation UIImage (Scale)
 
//等比率缩放
- (UIImage *)scaleImageToScale:(float)scale
{
    UIGraphicsBeginImageContext(CGSizeMake(self.size.width * scale, self.size.height * scale));
    [self drawInRect:CGRectMake(0, 0, self.size.width * scale, self.size.height * scale)];
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return scaledImage;
}

//自定长宽
- (UIImage*)scaleImageToSize:(CGSize)size
{
    UIGraphicsBeginImageContext(size);
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return scaledImage;
}

@end

使用

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- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    UIImage *imagePhoto = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData * imageData_before = UIImageJPEGRepresentation(imagePhoto,1);
    NSLog(@"Before : %d , %@",[imageData_before length]/1024,imagePhoto);
    
    imagePhoto = [imagePhoto scaleImageToSize:CGSizeMake(600, 600)];
    
    NSData * imageData_after = UIImageJPEGRepresentation(imagePhoto,1);
    NSLog(@"After : %d , %@",[imageData_after length]/1024,imagePhoto);
}

输出:
Before : 1504 , <UIImage: 0x796561e0> size {2560, 1600} orientation 0 scale 1.000000
After : 341 , <UIImage: 0x78e4e2f0> size {600, 600} orientation 0 scale 1.000000

效果图

（无）

备注

（无）