上传到服务器之前，如何在iOS上压缩/调整图像大小？

我目前正在使用Imgur在iOS上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"];

当我在模拟器中运行并从模拟器的图片库上传文件时，该代码可以正常工作，因为我处于快速以太网连接中。但是，选择使用iPhone拍摄的图像时，相同的代码在iPhone上超时。因此，我通过从网络上保存一个小图像并尝试将其上传的方式进行了尝试，该方法可以正常工作。

这使我相信iPhone拍摄的大图像正在通过速度较慢的3G网络超时。有没有办法在发送之前压缩/调整iPhone中的图像大小？

您应该可以通过执行以下操作来制作较小的图像

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

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

此代码段将调整图像的大小：

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

变量newSize是a CGSize，可以这样定义：

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

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。

为了补充@Tuan Nguyen，这也许是最快，最优雅的方法。

要链接到iphonedevelopertips.com上John Muchow的帖子，在UIImage中添加类别是一种非常便捷的方法，可以非常快速地进行缩放。刚打电话

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

返回您的NSDATA的640x480表示图像（可能是在线图像），而无需任何其他代码行。

Matt Gemmell的MGImageUtilities非常好，可以有效地调整大小并使用一些省力的方法。

在此代码中0.5表示50％...

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

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

Zorayr函数的快速实现（略有变化，以实际单位（不按比例缩放）包括高度或宽度约束）：

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
}

#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;
}

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

let orginalImage:UIImage = image

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

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

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。在这里，我使用的是0.5：原始---图片大小（字节）：85KB及之后---图片大小（字节）：23KB

-(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;
 }

这是方法调用

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

它返回该图像，您可以在任何地方显示该图像。