I am new to iOS, and I am trying a image on a view. The image in question is large, and fetched from a URL, so to load the view it takes quite some time (almost 5-10 sec).
I don't want to display a place holder and to do some asynchronous call to update the image;
instead, I want image processing similar to how it is implemented in the Facebook iOS app: the big image display hazy at first, slowly becoming the original image as it loads. Does anyone know how this can be achieved in iOS?
The 'hazy' image you talk about is a 'progressive' jpeg. You can re-format any arbitrary image to a progressive jpeg (on the server side), then use the Image I/O methods to display partial versions. There are a variety of techniques you could use - see this prior post for more pointers.
You can download and display a thumbnail image view first or just display a temporary loading image while you are downloading the big image. Take a look at ASIHTTP for asynchronous image downloading. There are several other frameworks available as well and tons of sample code if you take time to google.
Related
I want to store a bunch of images that are taken while the user uses the app, while making sure that I can view them with decently high resolution later on. And by "store", for now I don't need to store them past the closure of the app. Simply having them available after some point while the app is still alive is all I need.
I first tried simply storing the UIImages in their original size on the app, but then the app would crash after 7 or 8 pics were taken because of memory usage.
I then tried shrinking them (since my app has a grid display wherein I can see all the pictures, but shrunk to fit on a 3x3 grid of images) , and my app stopped crashing. But when I wanted the pictures to be viewed individually on full screen, the quality was terrible because I was enlarging a shrunk photo.
So I figured why not find a way to store the original image through another object in a way that wouldn't eat up too much memory. Searching online lead me to decide to store them in a file, by converting the images into NSData and then writing this into a file. BUT, when I would then load the NSData back into a UIImage, the orientation of my photos taken through the camera were all sideways! And after hours of looking (and failing) through how to transform it back into the proper orientation, I've decided to give up on trying to fix this orientation bug.
Instead, I just want to know if there is any other way for me to store large/high-res UIImages (without hogging up memory) besides using NSData. What ideas do you guys have?
And pardon me for having to write so much for a one-liner question. I just didn't want to get suggestions on doing something I've already tried.
Save it as a jpeg instead of a PNG, that way the image will be rotated for you. See https://stackoverflow.com/a/4868914/96683
I want to display a high resolution image in imageview. Here is what i do
Prepare UIImage in the background
When the file is loaded, switch to main thread
Display the image [ by using UIImageView's setImage: ]
The problem is there is a lag in the 3rd step. It takes few seconds and loads the file. And if its a large image, I get the memory warning and a crash. So is there a way by which i can draw images from top to bottom ( like how the browser does) ? Also I need to preserve the quality of the image.
Is there a way by which i can achieve my requirement. Thanks in advance
And if its a large image, I get the memory warning and a crash.
it seems you are hitting some "hard" (memory related) limit of your device trying to load and display the image into memory at once.
So is there a way by which i can draw images from top to bottom ( like how the browser does)?
You should try with CATiledLayer, which provides a way to draw very large images without incurring a memory hit.
Here you can find a tutorial about it.
You could also give a look at the PhotoScrollerNetwork project:
blazingly fast tile rendering - visually much much faster than Apple's code (which uses png files in the file system)
you supply a single jpeg file or URL and this code does all the tiling for you, quickly and painlessly
UIImage will not decode its underlying image data until it is actually requested, which will happen on the main thread when you assign it to an image view. So although you are trying to load the image in a background thread, the work is being delayed and actually occurs on the main thread.
The workarounds to this issue are pretty hacky and usually involve writing the image to a new graphics context to force the decoding, and then creating a CGImageRef or UIImage from that. This all takes place on the background thread. By the time you ship the new image to the main thread, all the decoding has already taken place and you shouldn't see a delay. This question has some answers which demonstrate this technique.
Drawing images from top-to-bottom is not possible with the standard APIs provided by Apple (as far as I know). You would have to write your own streaming image decoder which would be a significant task.
You can use SDWebImage framework which helps you for :
1.An asynchronous image downloader
2.Automatic image caching .
3.Avoid duplications .
You can download this from:https://github.com/rs/SDWebImage
About the memory warning it is not only due to your application its due to effective memory use from all the application running on the background so try to stop the background running applications.
I want to allow the user to select a photo, without limiting the size, and then edit it.
My idea is to create a thumbnail of the large photo with the same size as the screen for editing, and then, when the editing is finished, use the large photo to make the same edit that was performed on the thumbnail.
When I use UIGraphicsBeginImageContext to create a thumbnail image, it will cause a memory issue.
I know it's hard to edit the whole large image directly due to hardware limits, so I want to know if there is a way I can downsample the large image to less then 2048*2048 wihout memory issues?
I found that there is a BitmapFactory Class which has an inSampleSize option which can downsample a photo in Android platform. How can this be done on iOS?
You need to handle the image loading using UIImage which doesn't actually load the image into memory and then create a bitmap context at the size of the resulting image that you want (so this will be the amount of memory used). Then you need to iterate a number of times drawing tiles from the original image (this is where parts of the image data are loaded into memory) using CGImageCreateWithImageInRect into the destination context using CGContextDrawImage.
See this sample code from Apple.
Large images don't fit in memory. So loading them into memory to then resize them doesn't work.
To work with very large images you have to tile them. Lots of solutions out there already for example see if this can solve your problem:
https://github.com/dhoerl/PhotoScrollerNetwork
I implemented my own custom solution but that was specific to our environment where we had an image tiler running server side already & I could just request specific tiles of large images (madea server, it's really cool)
The reason tiling works is that basically you only ever keep the visible pixels in memory, and there isn't that many of those. All tiles not currently visible are factored out to the disk cache, or flash memory cache as it were.
Take a look at this work by Trevor Harmon. It improved my app's performance.I believe it will work for you too.
https://github.com/coryalder/UIImage_Resize
I am hiding a text file in an image using http://github.com/anirudhsama it works fine and I could able to extract the text file again back with my program.
But when I programmatically share the image in facebook, twitter and email, that shared image is not decode properly so I'm not getting the file back.
I retrive the image as follows:
UIImage *finalImageWithStegno = [UIImage imageWithContentsOfFile:fileName];
What I suspect is image compression when it is uploaded to the site. A simple way to check this is to hide a message in a cover image (obtain stego image). Upload the image on a website and download it. Compare the original stego image to the downloaded image. If they differ (byte by byte), there's your problem.
From a quick look at the code, it seems the app hides the data in the spatial domain, which is not robust. Your message is directly hidden in the image pixels and if they change (due to lossy compression, blurring, etc), your message will be lost. A solution to this would be to hide the data in the frequency domain. Another solution could be uploading the images with a filetype which doesn't get compressed? I don't know much how sites deal with images so the second suggestion may be impossible.
In any case, if uploading to a site distorts the image, look around for another app which may serve you unless you can code yourself. Then we can get into the specifics. :)
Your algorithm is not robust. Use Transform domain Stegnography to retain the information when its is re encoded. You may choose to embed in DCT coefficients or DWT Coefficients for better robustness.
In my website, I have a library contain all image of user, I want to display all image in this library. How can I do it?
I have solution but I can’t do it. This’s my solution. I’ll create thumbnail for each image and display it in library. Size of thumbnail is very small, so I don’t worry about performance. If I create thumbnail in my server. It must download, read and resize these images, then it return for my website. This way I feel not good. I have many images, each customer have about hundreds images, size of each image about 1mb or 2mb. I think have no server can handle it. Another way is create thumbnail on client by jQuery, but I can’t do it and my friend talk with me. jQuery don’t handle it. How can I do it for my solution? Hope you understand what I mean
I think you can use pagination if you would like to return million images in a page
so for instance 50 images per page to keep up with your web performance
You need to generate thumbnails on server and show thumbnails in the gallery. When a user clicks on a thumbnail in the gallery, show the full image.
I think your first idea is better. Because you don't want to show the images in actual size and you want to make them smaller. So using their thumbnail is a good solution. If you think this could add some complexity you can make the thumbnails for each image when user uploads them and in your view just use the thumbnails.