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
- //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:
- 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;
- }
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....