How to compress/resize image on iOS before uploading to a server?

问题

I\'m currently uploading an image to a server using Imgur on iOS with the following code:

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\"];

The code works fine when run in the simulator and uploading a file from the simulator\'s photo library because I\'m on a fast ethernet connection. However, the same code times out on the iPhone when selecting an image taken with the iPhone. So, I tried it by saving a small image from the web and attempting to upload that, which worked.

This leads me to believe the large images taken by the iPhone are timing out over the somewhat slow 3G network. Is there any way to compress/resize the image from the iPhone before sending it?

回答1:

You should be able to make a smaller image by doing something like

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

(for a quarter-size image) then convert the smaller image to a PNG or whatever format you need.

回答2:

This snippet will resize the image:

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

The variable newSize is a CGSize and can be defined like so:

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

回答3:

A self-contained solution:

- (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;
}

Thanks to @Tuan Nguyen.

回答4:

To complement @Tuan Nguyen, this is maybe the fastest and most elegant way to do that.

To link to John Muchow's post at iphonedevelopertips.com , adding a category to a UIImage is a very very handy way to scale in a very fast fashion. Just calling

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

returns you a 640x480 representation image of your NSDATA ( that could be an online image ) without any more line of code.

回答5:

Matt Gemmell's MGImageUtilities are very nice, resizing efficiently and with some effort-reducing methods.

回答6:

In this code 0.5 means 50% ...

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

回答7:

use this simple method NSData *data = UIImageJPEGRepresentation(chosenImage, 0.2f);

回答8:

Swift implementation of Zorayr's function (with a bit of a change to include height or width constraints by actual units not scale):

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
}

回答9:

#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;
}

回答10:

Swift 2.0 version of Jagandeep Singh method but need to convert data to image because NSData? is not converted UIImage automatically.

let orginalImage:UIImage = image

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

回答11:

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

回答12:

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;

try to convert JPG by scaling factor. Here I am using 0.5 In my case: Original --- Size of Image(bytes): 85KB & After --- Size of Image(bytes): 23KB

回答13:

-(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;
 }

This is the method calling

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

it returns image this image u can display any where...........

来源：https://stackoverflow.com/questions/4394491/how-to-compress-resize-image-on-ios-before-uploading-to-a-server

标签

ios

file-upload

ios4

uiimage

nsdata