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,公布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例如以下

1. //压缩图片质量
2. +(UIImage *)reduceImage:(UIImage *)image percent:(float)percent
3. {
4. NSData *imageData = UIImageJPEGRepresentation(image, percent);
5. UIImage *newImage = [UIImage imageWithData:imageData];
6. return newImage;
7. }
8. //压缩图片尺寸
9. + (UIImage*)imageWithImageSimple:(UIImage*)image scaledToSize:(CGSize)newSize
10. {
11. // Create a graphics image context
12. UIGraphicsBeginImageContext(newSize);
13. // new size
14. [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
15. // Get the new image from the context
16. UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
17. // End the context
18. UIGraphicsEndImageContext();
19. // Return the new image.
20. return newImage;
21. }

上面的方法比較常见，但是须要载入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,

我測试过上面方法,上面方法真不好用,真的不推荐大家用.那么我推荐以下这种方法:

1. static size_t getAssetBytesCallback(voidvoid *info, voidvoid *buffer, off_t position, size_t count) {
2. ALAssetRepresentation *rep = (__bridge id)info;
3. NSError *error = nil;
4. size_t countRead = [rep getBytes:(uint8_t *)buffer fromOffset:position length:count error:&error];
5. if (countRead == 0 && error) {
6. // We have no way of passing this info back to the caller, so we log it, at least.
7. NDDebug(@"thumbnailForAsset:maxPixelSize: got an error reading an asset: %@", error);
8. }
9. return countRead;
10. }
11. static void releaseAssetCallback(voidvoid *info) {
12. // The info here is an ALAssetRepresentation which we CFRetain in thumbnailForAsset:maxPixelSize:.
13. // This release balances that retain.
14. CFRelease(info);
15. }
16. // Returns a UIImage for the given asset, with size length at most the passed size.
17. // The resulting UIImage will be already rotated to UIImageOrientationUp, so its CGImageRef
18. // can be used directly without additional rotation handling.
19. // This is done synchronously, so you should call this method on a background queue/thread.
20. - (UIImage *)thumbnailForAsset:(ALAsset *)asset maxPixelSize:(NSUInteger)size {
21. NSParameterAssert(asset != nil);
22. NSParameterAssert(size > 0);
23. ALAssetRepresentation *rep = [asset defaultRepresentation];
24. CGDataProviderDirectCallbacks callbacks = {
25. .version = 0,
26. .getBytePointer = NULL,
27. .releaseBytePointer = NULL,
28. .getBytesAtPosition = getAssetBytesCallback,
29. .releaseInfo = releaseAssetCallback,
30. };
31. CGDataProviderRef provider = CGDataProviderCreateDirect((voidvoid *)CFBridgingRetain(rep), [rep size], &callbacks);
32. CGImageSourceRef source = CGImageSourceCreateWithDataProvider(provider, NULL);
33. CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(source, 0, (__bridge CFDictionaryRef) @{
34. (NSString *)kCGImageSourceCreateThumbnailFromImageAlways : @YES,
35. (NSString *)kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithInt:size],
36. (NSString *)kCGImageSourceCreateThumbnailWithTransform : @YES,
37. });
38. CFRelease(source);
39. CFRelease(provider);
40. if (!imageRef) {
41. return nil;
42. }
43. UIImage *toReturn = [UIImage imageWithCGImage:imageRef];
44. CFRelease(imageRef);
45. return toReturn;
46. }

採用上面的方法之后内存占用率非常低。

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

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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;

}

把上面的代码拷贝到project里面,然后调用这种方法就好了,例如以下图:

好了,有问题,欢迎评论给我.....

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