iOS 史上最全的图片压缩方法集合

  做上传图片功能,特别是类似于微信,QQ里面,发布9张图片, 少不了碰到一个问题,就是图片压缩问题,当然我也遇到了.

我研究了这个问题,发现网上普遍的方法是如下

 //压缩图片质量
+(UIImage *)reduceImage:(UIImage *)image percent:(float)percent
 {
    NSData *imageData = UIImageJPEGRepresentation(image, percent);
     UIImage *newImage = [UIImage imageWithData:imageData];
    return newImage;
 }
//压缩图片尺寸
 + (UIImage*)imageWithImageSimple:(UIImage*)image scaledToSize:(CGSize)newSize
{
     // Create a graphics image context
    UIGraphicsBeginImageContext(newSize);
     // new size
    [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
     // Get the new image from the context
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

    // End the context
     UIGraphicsEndImageContext();
    // Return the new image.
     return newImage;
}

上面的方法比较常见，可是需要加载到内存中来处理图片，当图片数量多了的时候就会收到内存警告，程序崩溃,

我测试过上面方法,上面方法真不好用,真的不推荐大家用.那么我推荐下面这个方法:

 static size_t getAssetBytesCallback(voidvoid *info, voidvoid *buffer, off_t position, size_t count) {
    ALAssetRepresentation *rep = (__bridge id)info;

    NSError *error = nil;
     size_t countRead = [rep getBytes:(uint8_t *)buffer fromOffset:position length:count error:&error];

     if (countRead == 0 && error) {
        // We have no way of passing this info back to the caller, so we log it, at least.
         NDDebug(@"thumbnailForAsset:maxPixelSize: got an error reading an asset: %@", error);
    }

    return countRead;
 }

 static void releaseAssetCallback(voidvoid *info) {
    // The info here is an ALAssetRepresentation which we CFRetain in thumbnailForAsset:maxPixelSize:.
     // This release balances that retain.
    CFRelease(info);
 }

 // Returns a UIImage for the given asset, with size length at most the passed size.
// The resulting UIImage will be already rotated to UIImageOrientationUp, so its CGImageRef
 // can be used directly without additional rotation handling.
// This is done synchronously, so you should call this method on a background queue/thread.
 - (UIImage *)thumbnailForAsset:(ALAsset *)asset maxPixelSize:(NSUInteger)size {
    NSParameterAssert(asset != nil);
     NSParameterAssert(size > 0);

     ALAssetRepresentation *rep = [asset defaultRepresentation];

     CGDataProviderDirectCallbacks callbacks = {
        .version = 0,
         .getBytePointer = NULL,
        .releaseBytePointer = NULL,
         .getBytesAtPosition = getAssetBytesCallback,
        .releaseInfo = releaseAssetCallback,
     };

     CGDataProviderRef provider = CGDataProviderCreateDirect((voidvoid *)CFBridgingRetain(rep), [rep size], &callbacks);
    CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, NULL);

    CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(source, 0, (__bridge CFDictionaryRef) @{
                                                                                                       (NSString *)kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                                                                                                      (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithInt:size],
                                                                                                       (NSString *)kCGImageSourceCreateThumbnailWithTransform : @YES,
                                                                                                      });
     CFRelease(source);
    CFRelease(provider);

    if (!imageRef) {
         return nil;
    }

    UIImage *toReturn = [UIImage imageWithCGImage:imageRef];

    CFRelease(imageRef);

    return toReturn;
 }

采用上面的方法之后内存占用率很低！

上面这么长的东西,大家一定看的很费劲,那么我直接上我源码,给大家看看,照着我的源码,写就好了.

static size_t getAssetBytesCallback(void *info, void *buffer, off_t position, size_t count) {

    ALAssetRepresentation *rep = (__bridge id)info;

    

    NSError *error = nil;

    size_t countRead = [rep getBytes:(uint8_t *)buffer fromOffset:position length:count error:&error];

    

    if (countRead == 0 && error) {

        // We have no way of passing this info back to the caller, so we log it, at least.

        NSLog(@"thumbnailForAsset:maxPixelSize: got an error reading an asset: %@", error);

    }

    

    return countRead;

}

static void releaseAssetCallback(void *info) {

    // The info here is an ALAssetRepresentation which we CFRetain in thumbnailForAsset:maxPixelSize:.

    // This release balances that retain.

    CFRelease(info);

}

//压缩图片

- (UIImage *)thumbnailForAsset:(ALAsset *)asset maxPixelSize:(NSUInteger)size

{

    NSParameterAssert(asset != nil);

    NSParameterAssert(size > 0);

    

    ALAssetRepresentation *rep = [asset defaultRepresentation];

    

    CGDataProviderDirectCallbacks callbacks =

    {

        .version = 0,

        .getBytePointer = NULL,

        .releaseBytePointer = NULL,

        .getBytesAtPosition = getAssetBytesCallback,

        .releaseInfo = releaseAssetCallback,

    };

    

    CGDataProviderRef provider = CGDataProviderCreateDirect((void *)CFBridgingRetain(rep), [rep size], &callbacks);

    

    CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, NULL);

    

    CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(source, 0, (__bridge CFDictionaryRef)

                                                              @{   (NSString *)kCGImageSourceCreateThumbnailFromImageAlways: @YES,

                                                                   (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithInt:size],

                                                                   (NSString *)kCGImageSourceCreateThumbnailWithTransform :@YES,

                                                                   });

    

    CFRelease(source);

    CFRelease(provider);

    

    if (!imageRef) {

        return nil;

    }

    

    UIImage *toReturn = [UIImage imageWithCGImage:imageRef];

    

    CFRelease(imageRef);

    

    return toReturn;

}

把上面的代码复制到工程里面,然后调用这个方法就好了,如下图:

好了,有问题,欢迎评论给我.....

本文部分内容参考自http://www.lyitnews.com/portal.php?mod=view&aid=1206,感谢他的分享....