I have an app which is photo-based, and had a ton of large-scaled resolution images on Parse. I currently have my app set up to grab these images from Parse with a query, and storing each photo into an UIImage array with a loop, and then displaying these photos in a UICollectionView.
It works great, if we are pulling less than 10 photos from Parse. However, if I am retrieving, say 20 photos, when I scroll down my UICollectonView after the photos have been loaded, around the 18th or so photo, my app will crash, and Xcodes console will output "Received memory warning".
What is the best practice for retrieving a large amount of large sized photos from Parse? (If you are displaying them in a UICollectionView)
I would download only the thumbnails. You can even do this using lazy loading (http://www.theappguruz.com/blog/ios-lazy-loading-images) if so inclined.
When the image is clicked on and you want to see it full size, then you download the full size image :)
Set a limit on how many images you want to retain in memory, and use a queue to decide when to store/get rid of the old images.
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I am making what can be described as an image manipulation app. My idea is that the user imports UIImages through the pod YPImagePicker and they are stored in two arrays, one for thumbnails and one for the fullsized images. A UICollectionView is then populated with the thumbnails and when the user taps the thumbnail the fullsized image is displayed in a UIImageView.
I am having memory issues with this solution. The RAM hits 300 MB on an iPhone X when I have roughly 10-12 images imported, which I have understood is too much. I guess it is because I store all the fullsized images in an array? Should I store the fullsized images on the users hard drive and not in RAM-memory? Or is there any way I can access the images from the users photo library and fetch the image when the user taps the thumbnail?
I know this is a stupid problem, but this is my first real app that I have to make, I have no one to ask and I looked up this problem and found no other similar problems.
My app crashes on real devices with no exception. I saw in the simulator that uses too much RAM and after a while I got to the conclusion that the pictures I am using are to blame.
The app is structured in this way: it has 8 viewControllers for different things: for example, it starts with one which lets the user select the avatar with which he/she will play and here I have two pictures, next is a viewController which shows the stats for that avatar and here it is another picture and so on. The problem is that each picture uses 40MB of RAM to be displayed and things add up so the app uses more than 300MB of RAM when the user gets to the gameviewCOntroller where the game is. Because of this, on devices like iPAD 2 or iphone 4 it crashes, but not on iphone 5.
I tried to set the images both from "images.xcassets" and from a ".atlas" folder, but the result is exactly the same. The pictures have a dimension of no more than 1500x1999px, they are in png format.
Also, I saw that if the app were to start directly into the gaveViewController it would use 180MB so the other viewController remain in memory or something like that. Should I "clear" them or something similar?
//-------update-------
This is what I got from Instruments:
Memory is a big deal on mobile devices, there is not a clear answer to you question, but I can give you some advices:
If your images are plain colors or have symmetric axes use resizable images. You can just use one line of pixel multiplied by with or height to cover the entire screen using a small amount of memory
Image compression doens't have effects when the image is decompressed. So if you have a png that is 600kb and you are thinking that converting in a 300kb will lower memory usage is only true for "disk space" when an image is decompressed in memory the size is widthXheightXNumber_of_channelXbit_for_channel
resize images: if are loading a 2000px square image into memory and you show it inside an image view of 800 px square, resize before adding it.You will have just a peak while resizing, but later it will use less memory
If you need to use big images, use tiling techniques such as CATiledLayer
If you don't need an image anymore get rid of it. It's ok to have an array of path to images, but not an array of full uncompressed images
Avoid -imageNamed it caches images and even if Apple says that this cache is released under memory pressure, you don't have a lot of control on it and it could be too late to avoid a crash
Those are general advices, it's up to you if they fit your requirements.
You should definitely follow Andrea's advices.
Additionally you should consider setting the image size to exactly what your need is. You're saying that you've tried to set them from xcassets so you have full control over the images you're loading, which is great (compared to downloading an image that you cannot modify).
I highly suggest you read some documentation on using Asset catalog files. This will allow you to have high-resolution image for bigger screens that also have more memory, and smaller ones for older devices, which is what you want here.
Also, note that 1500x1999px is still a very big size for most mobile devices.
More links about screen-size:
https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html
http://www.paintcodeapp.com/news/iphone-6-screens-demystified
I have an app that has 12 images contained in an array. All these images are displayed at the same time on the screen. (1 view - 12 much wider and higher images (UIImageView's) one on another. When user does something, app moves the images, thus the view displays different scenes)
The images themselves are not too heavy (it is about 2500x5000 in size, but the whole folder with images is around 3.5 MB).
After loading, the app consumes 355 MB.
When I put breakpoint in viewDidLoad (and all images are loaded at that time), xcode shows that the app consumes only 9 MB, but in viewDidAppear it is 355 MB.
What is the reason of it? And how can I store images compactly? (As I assume that the problem is in the images).
Thank you for any help!
An image open will occupy something like : H x W x number of channel x number of bit for channel, the file size is another thing, because images are compressed according to their type. Your images are 50Mb each one in memory.
The only way is to resize the image before displaing them. There are plenty of image resizing categories online, just google a little bit.
The other suggestion is to not load all the images togheter, just bring in the array the file path, and instantiate the image lazily.
If you need to use hires images you should look for CATiledLayer and tiling techniques.
These images probably cannot be displayed all at the same time onscreen, so you may want to load them only when necessary.
If you still need to display them all together onscreen, think about reducing their size.
Still, 355Mb is huge. Are you doing anything else in that application, that might use up all of that memory?
In Xcode go to Product->Profile. You will find there a lot of useful instruments which will help you to find problems with memory, CPU or battery usage. However, check it if you haven't seen it before.
I'm making a camera app in iOS. Everything is fine except from the memory usage. This is the flow of the "takeImageTask":
AVCaptureStillImageOutput -> NSData -> UIImage (which I crop and do other changes to) -> save to ALAssetsLibrary
I need to keep the UIImage in an array because I need to have them in a UICollectionView, and I have the possibility to show the images in a "big size" view.
This flow uses a lot of memory, so what I thought could be a better solution was to use the AssetURL I get from the AVCaptureStillImageOutput writeImageToSavedPhotosAlbum to fetch the images from the phone storage. My app also have the possibility to fetch images from the photo album by using UIImagePickerController, and I've noticed that this just uses a fraction of the memory compared to the "takeImageTask". I first made the app as an Android version, and there I just stored all the URLs, and used them to present images. Does anyone have any experience using asseturls to present images in iOS?
I need to keep the UIImage in an array because I need to have them in a UICollectionView, and I have the possibility to show the images in a "big size" view.
This is flawed logic. You might want to keep a minimal size thumbnail image in memory for the collection view, but you should even drop these from memory before the count gets too big. And the big images should be loaded from disk on demand because it is relatively infrequent and relatively expensive (using the asset URL is a good plan for this).
I'm building a camera application that saves the image data to a single JPEG file in the sandbox. The images average at about 2mb in size.
Problem : I cannot display the images in a photo viewer because having a few images in memory throws memory warnings and makes scrolling through the images very slow.
I cannot split the image into tiles and save them to disk because that's even more expensive than displaying the single image. I tried splitting the image up into tiles upon capture, but on the 5S it took, on average, 5 1/2 seconds to save all the tiles to disk. It will only get worse from there as the app is executed on older devices. This is very bad because what if the user exists the app in the middle of the save? I will have missing tiles and no uncompressed original file to find missing tiles later.
Question : what's the best way to show a full sized image without causing memory issues and keeping the scrolling fast? Tons of camera applications on the App Store do this and the Photos app does this, there has to be a good solution.
Note : I'm currently showing a thumbnail of the image and then loading the full size image from disk in another thread. Once the full size image loading has finished, I present the full size image on the main thread. This removes the memory issues because I only have one full size image in memory at once, with two thumbnails, but still causes lagging on the scrollview because drawing the full size image in the main thread is still pretty expensive.
I would greatly appreciate any input!
you could..
create a down sized thumb nail..
create a smaller image and save that in a different "sandbox" folder.. and read that for browsing.. then after that load the image if the user wants to look at it full size.
One way to deal with this is to tile the image.
You can save the large decompressed image to "disk" as a series of tiles, and as the user pans around pull out only the tiles you need to actually display. You only ever need 1 tile in memory at a time because you draw it to the screen, then throw it out and load the next tile. (You'll probably want to cache the visible tiles in memory, but that's an implementation detail. Even having the whole image as tiles may relieve memory pressure as you don't need one large contiguous block.)
This is how applications like Photoshop deal with this situation.
Second way which I suggest you is to
check the example from Apple for processing large images called PhotoScroller. The images have already been tiled. If you need an example of tiling an image in Cocoa check out cimgf.com
Hope this will helps you.