如何调整UIImage的大小以减少上传图像大小

Question

我一直在搜索谷歌，并且只会遇到减少高度/宽度的库或者通过CoreImage编辑UIImage外观的库。但我没有看到或找到一个库，帖子解释了如何减少图像大小，所以当它上传时，它不是完整的图像大小。

到目前为止我有这个：

        if image != nil {
        //let data = NSData(data: UIImagePNGRepresentation(image))
        let data = UIImagePNGRepresentation(image)
        body.appendString("--\(boundary)\r\n")
        body.appendString("Content-Disposition: form-data; name=\"image\"; filename=\"randomName\"\r\n")
        body.appendString("Content-Type: image/png\r\n\r\n")
        body.appendData(data)
        body.appendString("\r\n")
    }

它正在发送12MB的照片。我怎样才能减少到1mb？谢谢！

Answer 1

使用此方法，您可以控制所需的大小：

func jpegImage(image: UIImage, maxSize: Int, minSize: Int, times: Int) -> Data? {
    var maxQuality: CGFloat = 1.0
    var minQuality: CGFloat = 0.0
    var bestData: Data?
    for _ in 1...times {
        let thisQuality = (maxQuality + minQuality) / 2
        guard let data = image.jpegData(compressionQuality: thisQuality) else { return nil }
        let thisSize = data.count
        if thisSize > maxSize {
            maxQuality = thisQuality
        } else {
            minQuality = thisQuality
            bestData = data
            if thisSize > minSize {
                return bestData
            }
        }
    }
    return bestData
}

方法调用示例：

jpegImage(image: image, maxSize: 500000, minSize: 400000, times: 10)  

它将尝试在maxSize和minSize的最大和最小大小之间获取文件，但只尝试次数。如果在这段时间内失败，它将返回零。

Answer 2

我认为swift本身最简单的方法就是将图像压缩成压缩数据，这是swift 4.2中的代码

let imageData = yourImageTobeCompressed.jpegData(compressionQuality: 0.5)

并且您可以发送此imageData以上传到服务器。

Answer 3

Objective-C中相同：

界面：

@interface UIImage (Resize)

- (UIImage *)resizedWithPercentage:(CGFloat)percentage;
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality;

@end

实施：

#import "UIImage+Resize.h"

@implementation UIImage (Resize)

- (UIImage *)resizedWithPercentage:(CGFloat)percentage {
    CGSize canvasSize = CGSizeMake(self.size.width * percentage, self.size.height * percentage);
    UIGraphicsBeginImageContextWithOptions(canvasSize, false, self.scale);
    [self drawInRect:CGRectMake(0, 0, canvasSize.width, canvasSize.height)];
    UIImage *sizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return sizedImage;
}

- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality {
    NSData *imageData = isPng ? UIImagePNGRepresentation(self) : UIImageJPEGRepresentation(self, compressionQuality);
    if (imageData && [imageData length] > 0) {
        UIImage *resizingImage = self;
        double imageSizeKB = [imageData length] / weight;

        while (imageSizeKB > weight) {
            UIImage *resizedImage = [resizingImage resizedWithPercentage:0.9];
            imageData = isPng ? UIImagePNGRepresentation(resizedImage) : UIImageJPEGRepresentation(resizedImage, compressionQuality);
            resizingImage = resizedImage;
            imageSizeKB = (double)(imageData.length / weight);
        }

        return resizingImage;
    }
    return nil;
}

用法：

#import "UIImage+Resize.h"

UIImage *resizedImage = [self.picture resizeTo:2048 isPng:NO jpegCompressionQuality:1.0];

Answer 4

当我尝试使用接受的答案调整图像大小以便在我的项目中使用时，它会出现非常像素化和模糊的情况。我最终得到了这段代码来调整图像大小而不添加像素化或模糊：

func scale(withPercentage percentage: CGFloat)-> UIImage? {
        let cgSize = CGSize(width: size.width * percentage, height: size.height * percentage)

        let hasAlpha = true
        let scale: CGFloat = 0.0 // Use scale factor of main screen

        UIGraphicsBeginImageContextWithOptions(cgSize, !hasAlpha, scale)
        self.draw(in: CGRect(origin: CGPoint.zero, size: cgSize))

        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        return scaledImage
    }

Answer 5

extension UIImage {
func resized(toValue value: CGFloat) -> UIImage {
    if size.width > size.height {
        return self.resize(toWidth: value)!
    } else {
        return self.resize(toHeight: value)!
    }
}

Answer 6

使用.resizeToMaximumBytes调整UIImage的大小