I am loading a UIImage of size 2480 × 3508 into UIImageView using UIViewContentModeScaleAspectFit. I am getting memory warning while loading this image. And after i loaded a few images of this size in this UIImageView the application crashes. Is there any method to solve this.
Solution to this problem consists of either loading scaled version of the image (*1) or you have option to display it in full resolution with help of CATiledLayer(*2).
[UIImage imageWithCGImage:scale:orientation:];
CATiledLayer example
Addendum: If your image source is Photo Library, ALASSet provides already scaled image to full screen and full resolution image. You can use combination of both with CATiledLayer. Full screen image is added to layer beneath the CATiledLayer to serve as placeholder while you're waiting for tiles in CATiledLayer to load.
Well, according to the documentation :
You should avoid creating UIImage objects that are greater than 1024 x 1024 in size.
Reduce your image then load it in your ImageView, there are plenty of libraries to do this, here is one :
https://github.com/Nyx0uf/NYXImagesUtilities
You can use this for scaling
The method is described simply in the following link:
How to scale a UIImageView proportionally?
Related
I'm working on a comic viewer app that downloads the latest content from a server. It downloads a single file regardless of the screen scale. What I'd like to do is make this file work correctly on both screens.
What's the procedure for this and how should I size the photos to fit? The trouble I'm having is that the graphics are retina screen size, but the iPhone doesn't interpret them as such. That means they're displayed twice as large as they should be.
CGImageRef cgImage = [myImage cgImage];
UIImage *retinaImage = [UIImage imageWithCGImage:cgImage scale:2.0 orientation:UIImageOrientationUp];
You could also change your image's dpi value in an image editor to make UIImage recognize the scale automatically.
Generally though, you should use lower-resolution images on devices that don't have a retina display because otherwise you're wasting precious memory.
For normal screen, you can resize them programmatically, by adding a scale category to the UIImage class by example, there are many code samples on stackoverflow like :
UIImage resize (Scale proportion)
For retina, you need to set the scale of the UIImage to let the ios know for what screen size it is used (you can set this with the initWithCGImage:scale:orientation: method of UIImage).
I have a table where the cells' image views are being populated by images that have been previously pulled down off a server. So:
[[cell imageView] setImage:[[[UIImage alloc] initWithContentsOfFile:filePath] autorelease]];
Where "filePath" is the location of these images. Working beautifully, until I decided to be clever and add retina display images to my server. These images (double-sized, obviously) are being displayed, but are shrunk. I had labelled them image#2x.png, hoping that the iPhone would just know what to do with them, but obviously that doesn't work in this context.
I've looked at the discussions, and am guessing I need to do something with the contentsScale of the cell's imageView, like matching it to the screen scale, but I'm not sure exactly how to do this. Any help appreciated.
From server you cannot download automatically retina images.
You need a control like
if (iphone == 4) image=img#2x.png
else image=img.png
to get correct images.
You would need to set the scale factor of the image correctly. Please check the scale property in UIImage
If you load an image from a file whose
name includes the #2x modifier, the
scale is set to 2.0. If the filename
does not include the modifier but is
in the PNG or JPEG format and has an
associated DPI value, a corresponding
scale factor is computed and reflected
in this property. You can also specify
an explicit scale factor when
initializing an image from a Core
Graphics image. All other images are
assumed to have a scale factor of 1.0.
So you can read your image as above, get the CGImage from it and create a new UIImage using + (UIImage *)imageWithCGImage:(CGImageRef)imageRef scale:(CGFloat)scale orientation:(UIImageOrientation)orientation.
A nicer way could be to check the DPI of your retina image and make it 144dpi with a graphics program. According to the scale property documentation this might work, too.
I am using following code to resize an image - it all works well and as expected...
Resize UIImage the right way
I use interpolation quality as kCGInterpolationLow and UIImageJPEGRepresentation(image,0.0) to get the NSData of that image.
The problem is that the image size is still a bit high in size at around 100kb.
My question is can I reduce it further?
The images originate from the iPhone Photo Album and are selected via a imagePickerController.
Many thanks,
I am trying to improve scrolling performance of a UITableView. I am loading the images using imageNamed: and dispatch_async, but scrolling is very good once the images have been loaded into the cells. I would like to fade in the images only if they are not in the system cache to reduce the jarring effect of the images "popping" into view.
Is there a way to know if an image is already in the system cache?
There is no documented way to look inside the UIImage to check such things.
I think the only way to know for sure that the image is available immediately, is to force the UIImage to be loaded. This can be done in the background, by creating the UIImage and accessing it's pixels, using CGImage functions. If you ensure that there is no rescaling needed (i.e. don't put a 3000x2000 image in a 30x20 space) then it should display without a glitch.
I want to show some images as a thumbnail in View controller but i dont know how to do this. Can anyone please give me some ideas or sample code if possible.
Are you asking how to create thumbnails from larger images, or about how to build a view controller which displays them nicely?
Building a view controller:
You could use TTPhotoViewController from the Three20 project (description), which acts similarly to the iPhone's built in camera roll to view images.
You can look at the Scrolling sample code from apple, referred to in this question about using it for thumbnails.
If you want to build one yourself, you might consider using a GridView from the moriarty library, either as a large grid in a UIScrollView, or on a more efficient row-by-row basis in a UITableView. There's a previous question on optimized image loading in a UIScrollView.
Creating thumbnails from larger images:
The code-easiest way to scale down an image is to simply display it in a UIImageView with a frame set to the smaller size that you want - it's scaled for you.
If you want to save a thumbnail, or care about memory usage, you can create a hard-scaled version. The sample code below is taken from this blog post, and can be added to UIImage as a category method:
- (UIImage*) imageScaledToSize: (CGSize) newSize {
UIGraphicsBeginImageContext(newSize);
[self drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
Finally, here's a previous question on masking out round corners on an image, similar to the app icons used on the home screen.
Added
Using an image's built-in thumbnail:
There's a nice function called CGImageSourceCreateThumbnailAtIndex that understands built-in thumbnails in certain image data formats. You can see some useful sample code for this under Creating a Thumbnail Image from an Image Source in the Image I/O Programming Guide from Apple.
There are multiple issues with thumbnails; perhaps you could clarify which ones you are most concerned about?
How to display a smaller version of an existing image
How to speed up paging by caching the thumbnails (instead of just dynamically shrinking the originals)
How to allow the user to page through the thumbnails
How to synchronize the thumbnails with the originals, in the event that your images are editable or the user can add to them