Question

我正在编写一个iPhone应用程序来创建一个屏幕截图并将其作为png或jpg发送。如何压缩图像以减小文件大小？

以下是我拍摄图片的代码：

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

类似的问题是answered here on the Stack。唯一的区别是你正在使用UIImage，但这不应该让你退缩，我认为一般的方法仍然可以工作。您甚至可以以编程方式设置压缩因子。

希望这有帮助！

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

我怎样才能压缩UIImage？

2 个答案: