如何壓縮UIImage？

Question

我正在寫一個iPhone應用程序來創建一個屏幕截圖，並將它作爲PNG或JPG格式郵件。如何壓縮圖像以減小文件大小？

這裏是我的捕捉圖像代碼：

UIGraphicsBeginImageContext(containerView.frame.size); 
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()]; 
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext(); 
UIGraphicsEndImageContext(); 

// launch mail app 
[self performSelector:@selector(sendImage:) withObject:viewImage afterDelay:0.5]; 

Answer 1

類似的問題是answered here on the Stack。唯一的區別是你使用UIImage，但這不應該阻礙你，我認爲一般的方法仍然可以工作。你甚至可以編程設置壓縮因子。

希望這會有所幫助！

Answer 2

#import "UIImage+Compress.h" 

#define MAX_IMAGEPIX 200.0   // max pix 200.0px 
#define MAX_IMAGEDATA_LEN 50000.0 // max data length 5K 

@implementation UIImage (Compress) 

- (UIImage *)compressedImage { 
    CGSize imageSize = self.size; 
    CGFloat width = imageSize.width; 
    CGFloat height = imageSize.height; 

    if (width <= MAX_IMAGEPIX && height <= MAX_IMAGEPIX) { 
     // no need to compress. 
     return self; 
    } 

    if (width == 0 || height == 0) { 
     // void zero exception 
     return self; 
    } 

    UIImage *newImage = nil; 
    CGFloat widthFactor = MAX_IMAGEPIX/width; 
    CGFloat heightFactor = MAX_IMAGEPIX/height; 
    CGFloat scaleFactor = 0.0; 

    if (widthFactor > heightFactor) 
     scaleFactor = heightFactor; // scale to fit height 
    else 
     scaleFactor = widthFactor; // scale to fit width 

    CGFloat scaledWidth = width * scaleFactor; 
    CGFloat scaledHeight = height * scaleFactor; 
    CGSize targetSize = CGSizeMake(scaledWidth, scaledHeight); 

    UIGraphicsBeginImageContext(targetSize); // this will crop 

    CGRect thumbnailRect = CGRectZero; 
    thumbnailRect.size.width = scaledWidth; 
    thumbnailRect.size.height = scaledHeight; 

    [self drawInRect:thumbnailRect]; 

    newImage = UIGraphicsGetImageFromCurrentImageContext(); 

    //pop the context to get back to the default 
    UIGraphicsEndImageContext(); 

    return newImage; 

} 

- (NSData *)compressedData:(CGFloat)compressionQuality { 
    assert(compressionQuality <= 1.0 && compressionQuality >= 0); 

    return UIImageJPEGRepresentation(self, compressionQuality); 
} 

- (CGFloat)compressionQuality { 
    NSData *data = UIImageJPEGRepresentation(self, 1.0); 
    NSUInteger dataLength = [data length]; 

    if(dataLength > MAX_IMAGEDATA_LEN) { 
     return 1.0 - MAX_IMAGEDATA_LEN/dataLength; 
    } else { 
     return 1.0; 
    } 
} 

- (NSData *)compressedData { 
    CGFloat quality = [self compressionQuality]; 

    return [self compressedData:quality]; 
} 

@end