如何在上传到服务器之前在 iOS 上压缩/调整图像大小？

Question

我目前正在使用 iOS 上的 Imgur 使用以下代码将图像上传到服务器：

NSData* imageData = UIImagePNGRepresentation(image);
NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString* fullPathToFile = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"SBTempImage.png"];
[imageData writeToFile:fullPathToFile atomically:NO];

[uploadRequest setFile:fullPathToFile forKey:@"image"];

在模拟器中运行并从模拟器的照片库上传文件时，代码运行良好，因为我使用快速以太网连接。但是，当选择用 iPhone 拍摄的图像时，相同的代码在 iPhone 上会超时。因此，我尝试从网络上保存一张小图像并尝试上传该图像，结果成功了。

这让我相信 iPhone 拍摄的大图像在速度较慢的 3G 网络上会超时。有什么方法可以在发送之前压缩 iPhone 中的图像/调整其大小吗？

Answer 1

此代码片段将调整图像大小：

UIGraphicsBeginImageContext(newSize);
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

变量 newSize 是一个 CGSize ，可以像这样定义：

CGSize newSize = CGSizeMake(100.0f, 100.0f);

Answer 2

一个独立的解决方案：

- (UIImage *)compressForUpload:(UIImage *)original scale:(CGFloat)scale
{
    // Calculate new size given scale factor.
    CGSize originalSize = original.size;
    CGSize newSize = CGSizeMake(originalSize.width * scale, originalSize.height * scale);

    // Scale the original image to match the new size.
    UIGraphicsBeginImageContext(newSize);
    [original drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *compressedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return compressedImage;
}

感谢@Tuan Nguyen。

Answer 3

为了补充@Tuan Nguyen，这可能是最快、最优雅的方法。

链接到 John Muchow 的帖子iphonedevelopertips.com，向 UIImage 添加类别是一种非常非常方便的快速扩展方式。
只需调用

    UIImage *_image = [[[UIImage alloc] initWithData:SOME_NSDATA] scaleToSize:CGSizeMake(640.0,480.0)];

即可返回 NSDATA 的 640x480 表示图像（可能是在线图像），无需任何更多代码行。

Answer 4

Matt Gemmell 的 MGImageUtilities 非常好，可以有效地调整大小并使用一些减少工作量的方法。

Answer 5

在此代码中 0.5 表示 50% ...

UIImage *original = image;
UIImage *compressedImage = UIImageJPEGRepresentation(original, 0.5f);

Answer 6

使用这个简单的方法 NSData *data = UIImageJPEGRepresentation(chosenImage, 0.2f);

Answer 7

Zorayr 函数的快速实现（进行了一些更改，以包括实际单位而非比例的高度或宽度约束）：

class func compressForUpload(original:UIImage, withHeightLimit heightLimit:CGFloat, andWidthLimit widthLimit:CGFloat)->UIImage{

    let originalSize = original.size
    var newSize = originalSize

    if originalSize.width > widthLimit && originalSize.width > originalSize.height {

        newSize.width = widthLimit
        newSize.height = originalSize.height*(widthLimit/originalSize.width)
    }else if originalSize.height > heightLimit && originalSize.height > originalSize.width {

        newSize.height = heightLimit
        newSize.width = originalSize.width*(heightLimit/originalSize.height)
    }

    // Scale the original image to match the new size.
    UIGraphicsBeginImageContext(newSize)
    original.drawInRect(CGRectMake(0, 0, newSize.width, newSize.height))
    let compressedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return compressedImage
}

Answer 8

#import <ImageIO/ImageIO.h>
#import <MobileCoreServices/MobileCoreServices.h>

+ (UIImage *)resizeImage:(UIImage *)image toResolution:(int)resolution {
NSData *imageData = UIImagePNGRepresentation(image);
CGImageSourceRef src = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
CFDictionaryRef options = (__bridge CFDictionaryRef) @{
                                                       (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                       (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                       (id) kCGImageSourceThumbnailMaxPixelSize : @(resolution)
                                                       };
CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, options);
CFRelease(src);
UIImage *img = [[UIImage alloc]initWithCGImage:thumbnail];
return img;
}

Answer 9

Swift 2.0 版本的 Jagandeep Singh 方法但需要将数据转换为图像，因为 NSData？不会自动转换 UIImage。

let orginalImage:UIImage = image

let compressedData = UIImageJPEGRepresentation(orginalImage, 0.5)
let compressedImage = UIImage(data: compressedData!)

Answer 10

NsData *data=UiImageJPEGRepresentation(Img.image,0.2f);

Answer 11

UIImage *image = [UIImage imageNamed:@"image.png"];
NSData *imgData1 = UIImageJPEGRepresentation(image, 1);
NSLog(@"Original --- Size of Image(bytes):%d",[imgData1 length]);

NSData *imgData2 = UIImageJPEGRepresentation(image, 0.5);
NSLog(@"After --- Size of Image(bytes):%d",[imgData2 length]);
image = [UIImage imageWithData:imgData2];
imgTest.image = image;

尝试按比例因子转换 JPG。这里我用的是0.5
就我而言：
原始 --- 图像大小（字节）：85KB &之后 --- 图像大小（字节）：23KB

Answer 12

-(UIImage *) resizeImage:(UIImage *)orginalImage resizeSize:(CGSize)size
{
CGFloat actualHeight = orginalImage.size.height;
CGFloat actualWidth = orginalImage.size.width;
//  if(actualWidth <= size.width && actualHeight<=size.height)
//  {
//      return orginalImage;
//  }
float oldRatio = actualWidth/actualHeight;
float newRatio = size.width/size.height;
if(oldRatio < newRatio)
{
    oldRatio = size.height/actualHeight;
    actualWidth = oldRatio * actualWidth;
    actualHeight = size.height;
}
else
{
    oldRatio = size.width/actualWidth;
    actualHeight = oldRatio * actualHeight;
    actualWidth = size.width;
}

CGRect rect = CGRectMake(0.0,0.0,actualWidth,actualHeight);
UIGraphicsBeginImageContext(rect.size);
[orginalImage drawInRect:rect];
orginalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return orginalImage;
 }

这是调用它的方法

 UIImage *compimage=[appdel resizeImage:imagemain resizeSize:CGSizeMake(40,40)];      

返回图像，该图像可以在任何地方显示......

Answer 13

您应该能够通过执行类似的操作

UIImage *small = [UIImage imageWithCGImage:original.CGImage scale:0.25 orientation:original.imageOrientation];

（对于四分之一大小的图像）来制作较小的图像，然后将较小的图像转换为 PNG 或您需要的任何格式。