I am showing all the images from the camera roll in my iPhone app. I build an array of ALAsset * that contains the list of all images in the camera roll when the app starts. I form cells by loading these images in a image view:
// Get the full resolution image for asset
ALAssetRepresentation *assetRep = [asset defaultRepresentation];
UIImage *image = [UIImage imageWithCGImage:[assetRep fullResolutionImage]];
[cell.imageCropper setImage:image];
I do this when a new cell is requested in
- (AQGridViewCell *) gridView: (AQGridView *) aGridView cellForItemAtIndex: (NSUInteger) index
The problem is that it lags when there are many images and the user scrolls quickly through the images. What is the correct way of handling this?
Consider loading the images in the background using GCD.
Maybe this helps: loading images from a background thread using blocks
Use thumbnail instead of fullResolutionImages
Related
Using ALAssetsLibrary the Thumbnail images takes time to load.is there any solution to load images faster.
the images are more than 900 images in photos.
Code:
[ALAssetsGroupObj enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger i, BOOL *load)
{
if(asset == nil)
{
asset;
}
UIImage* thumbImage = [UIImage imageWithCGImage:[asset thumbnail]
}
Thanks
No, there is no way to make it go any faster. But there are a few tricks:
Cache them to a static NSDictionary. Next time you'll need to draw them in your app, it will be much faster than pulling them from the library. I've tried with far more than 900 thumbnails.
Your screen won't fit 900 thumbs. As the user scrolls, you can populate the images in blocks and load say 16-32 or so per time. This is a bit tricky though as both the operation to draw the thumbnails and the scrolling needs to run on the main thread.
I am loading image with data in my table view. Images are coming from web. I created method to get image url in model class.Model class has Nsdictionary and objects.
But this images is slowing down scrolling .Here is my code
UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:#"%#",
[(Tweet *)[recentTweets objectAtIndex:indexPath.row]urlString]]]]];
cell.imageView.image = image;
Please tell Where I am going wrong?
Use lazy loading and do your own drawing. Try to understand the techniques on the sample projects I linked. These are the best ways to improve the performance of tables with images.
here is the methodology I use for loading images into a UITableView from a remote location:
in your .h file, declare a mutable dictionary for storing the images:
NSMutableDictionary *images;
initialize the dictionary in -init... or in -viewDidLoad
images = [[NSMutableDictionary alloc]init];
in the .m, tableView:cellForRowAtIndexPath:, see if the image exists in your dictionary for the indexPath
UIImage *img = [images objectForKey: indexPath];
if the image does exist, just set it.
if (img) cell.imageView.image = img;
if the image does NOT exist, set the cell's image to a temporary image...
if (!img) cell.imageView.image = [UIImage imageNamed:#"imageUnavailable.png"];
AND add that image to your dictionary so it doesnt try to refetch the image if you scroll off and back to that image before it loads...
[images setObject:[UIImage imageNamed:#"imageUnvailable.png"] forKey: indexPath];
then, in this same block, use an NSOperationQueue, and a custom NSOperation ( here is a reference - NSOperation and SetImage) to get your image and call back into your UITableViewController with that image.
in your callback, add your image to the dictionary (overwriting the temp image) and call [tableView reloadData]
this will give you a nice non blocking user experience.
The are a couple of ways how to do it. I had the best experience with a Queue for the HttpRequests, which I pause during the scrolling process.
I highly recommend this framework for that:
http://allseeing-i.com/ASIHTTPRequest/
I also implemented an image cache, which only loads the images if there weren't in the cache.
And the last tweak was to actually draw the images instead of using a high level uicomponent like the UIImageView
The number one reason your code is slow right now is because you're making a network call on the main thread. This blocks an UI from being updated and prevents the OS from handling events (such as taps).
As already suggested, I recommend ASIHTTPRequest. Combine asynchronous requests with an NSOperationQueue with a smaller concurrency count (say, 2) for the image requests, caching, and reloading the rows when images come in (on the main thread) (also only reloading the row if its currently visible). You can get a smooth scrolling table view.
I have an example of this on github here: https://github.com/subdigital/iphonedevcon-boston
It's in the Effective Network Programming project and includes a set of projects that progressively improve the experience.
Download the images before you load the tableView, and store them in an NSArray. Then when the cellForRowAtIndexPath method is called, show a loading image until the image is in the array.
I'm trying to emulate the animation seen in the default camera app, where a snapshot of the cameras viewfinder is animated into the corner of the apps display.
The AVCaptureVideoPreviewLayer object that holds the key to solving this problem isn't very open to these requirements: trying to create a copy of it in a new layer with ..
- (id)initWithLayer:(id)layer
.. returns an empty layer, without the image snapshot, so clearly there is some deeper magic going on here.
Your clues/boos are most welcome.
M.
facing the same woes, from a slightly different angle.
Here are possible solutions, that none are too great IMO:
You can add to an AVCaptureSession both an AVCaptureStillImageOutput and an AVCaptureVideoDataOutput. When you set the sessionPreset to AVCaptureSessionPresetHigh you'll start getting frames by the API, and when you switch to AVCaptureSessionPresetPhoto you can take real images. So right before taking the picture, you can switch to video, get a frame, and then return to camera. Major caveat is that it takes a "long" time (couple of seconds) for the camera to switch between the video camera and picture camera.
Another option would be to use only the camera output (AVCaptureStillImageOutput), and use UIGetScreenImage to get a screen capture of the phone. You could then crop out the controls and leave only the image. This gets complicated if you're showing UI controls over the image. Also, according to this post, Apple started rejecting apps that use this function (it was always iffy).
Aside from these I also tried playing with AVCaptureVideoPreviewLayer. There's this post to save a UIView or CALayer to a UIImage. But it all produces clear or white images. I tried accessing the layer, the view's layer, the superlayer, the presentationLayer, the modelLayer, but to no avail. I guess the data in AVCaptureVideoPreviewLayer is very internal, and not really part of the regular layer infrastructure.
Hope this helps,
Oded.
I think you should add an AVCaptureVideoDataOutput to the current session with:
AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init];
videoOutput.videoSettings = #{ (NSString *)kCVPixelBufferPixelFormatTypeKey : #(kCVPixelFormatType_32BGRA) };
[session addOutput:videoOutput];
dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);
[videoOutput setSampleBufferDelegate:self queue:queue];
dispatch_release(queue);
Then, implement the delegate method below to get your image snapshot:
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
// Add your code here that uses the image.
dispatch_async(dispatch_get_main_queue(), ^{
_imageView.image = image;
});
}
This will consume memory and reduce the performance of the app. To improve, you can also optimize your AVCaptureVideoDataOutput with:
videoOutput.minFrameDuration = CMTimeMake(1, 15);
You can also use alwaysDiscardsLateVideoFrames.
there are 2 ways to grab frames of the preview.. AVCaptureVideoDataOutput & AVCaptureStillImageOutput :)
is your capture session is setup to grab video frames, then make your layer with the cgimage from a chosen frame. if it's setup for stills, wait until getting your still image and make your layer from a scaled down version of that cgimage. if you don't have an output on your session yet, you'll have to add one i think.
Starting in iOS 7, you can use UIView::snapshotViewAfterScreenUpdates to snapshot the UIView wrapping your AVCaptureVideoPreviewLayer. This is not the same as UIGetScreenImage, which will get your app rejected.
UIView *snapshot = [self.containerView snapshotViewAfterScreenUpdates:YES];
Recall the old-school way of turning a view into an image. For some reason it worked on everything except for camera previews:
UIGraphicsBeginImageContextWithOptions(self.containerView.bounds.size, NO, [UIScreen mainScreen].scale);
[self.containerView drawViewHierarchyInRect:self.containerView.bounds afterScreenUpdates:YES];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
I have a UIImageView, which pics up different images from the web, they are all different res. I have them to display as Aspect fit so that the whole picture displays even if it means leaving empty space on top or sides.
What i want to have the feature of doing is, once its displayed, to zoom in and out using the pinch or any other way.
NSURL* iURL = [NSURL URLWithString:tURL];
NSData* iData = [NSData dataWithContentsOfURL:iURL];
UIImage* iImage;
iImage = [UIImage imageWithData:iData];
FullScreenImage.image = iImage;
All this code is being executed on another thread, then it returns to the main thread and is displayed on a view using
[navigationController pushViewController:vFullscreen animated:YES];
Thanks for the help
You will need to use a UIScrollView as UIImageView does not offer any built-in zooming. See the Apple example entitled: ScrollViewSuite
I am making an app that adds a picture frame to a photo.
I would like to know how to have my Save button save both Images (the photo, and the frame) as one Image.
Right now it only saves one of the images.
In interface builder I have the save action saving the image that is loaded into an ImageView, with the frame ImageView overlaying that image.
I'd like to merge the two photos as one, so the save action can save the image with the frame.
Thanks!
If you've displayed the frame over the photo in your UI, just use UIScreenGetImage something like
...
CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
// You could, e.g., save the captured image to photo album
UIImageWriteToSavedPhotosAlbum(image, self, #selector(image:didFinishSavingWithError:contextInfo:), nil);
This probably isn't what you want, but if you load both images into OpenGL (there's a nice Apple sample that loads images in OpenGL), lay one on top of the other, and then write the result to an image (excellent tutorial here - http://www.bit-101.com/blog/?p=1861).
You don't even need to render it to the screen, so there's no fiddling around with EAGL.