I'm working on an iPhone App that uses the camera to take pictures, then I'm saving them to the Applications Documents directory. I'm using the following code to convert the UIImage to NSData,
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(image)];
Then I write the NSData using
[imageData writeToFile:path atomically:NO]
It all works. The problem is that UIImagePNGRepresentation() is really slow. It takes 8-9 secs on my 3G to convert the image to NSData. This seems wrong to me. Does anyone have any experience with this? Is this just slow function or am I doing something terribly wrong?
Thanks
Are you sure you want to save pictures captured with the camera as PNG?
JPEG is a more appropriate format for photographs. Additionally, its likely much faster!
Related
Well this may be a very easy Question but I'm not getting the answer after searching a lot.
I have one application in which I send the image taken from camera. The path of image captured from camera is stored in database. So in mail attachment code I load image from path and attach like this:
UIImage *myImage = [UIImage imageWithContentsOfFile:ImagePath];
NSData *imageData = UIImagePNGRepresentation(myImage);
[mailer addAttachmentData:imageData mimeType:#"image/png" fileName:#"Spotted"];
but the image is rotated by 90 Degree left every time. Can anyone guide me what am I doing wrong here??
P.S.: NSLog of ImagePath -->
/var/mobile/Applications/4BFB1BD9-DD83-42AF-A2BF-A5E4CC0DEAE3/Documents/459443.png
There has been some discussion on the Apple site about this issue in pictures sent by mail.
Unless you need it to be a PNG, I suggest converting it to a JPEG. JPEGs are more compressed (useful when it comes to email) and don't seem to have this rotating problem. Try using NSData *imageData = UIImageJPEGRepresentation(myImage); instead.
I've twisted my brain on this problem for several days as well. If you need it to be a PNG, here's a pretty good write up of what I learned on the topic: iOS PNG Image rotated 90 degrees
On the iPhone I saved an image to the photo library with modifications (appending data after the image code) using the assest library to save the NSData directly to the photo library. Now I want to read the image back from the photo library as an NSData to read it. If I read it as a UIImage, it changes the data inside the image.
How can I read the photo from the photo library as NSData? I tried looking into the reference URL in 4.1 but no luck.
Edit: I edited to explain why I'm saving it as an NSData. The URL method in the answers works if you just want pure NSData, but does not help in the context that I am asking.
Edit 2: The answer with the getBytes was the answer that did it for me. The code I used was:
int8_t *bytes = malloc([representation size]);
NSUInteger length = [representation getBytes:bytes fromOffset:0 length:[representation size] error:&error];
This was able to get me everything inside the file which gave me the image code PLUS what I added in NSData form.
Edit 3:
Is there a way to do this now in iOS 10 with the PHPhotoLibrary which replaces AssetLibrary? I need the image in NSData being the original RAW image with no modifications.
You should look into the getBytes method of ALAssetRepresentation.
This gives you the original RAW image data of your image and also makes it possible to use a buffer to process the image instead of reading the image into memory all at once.
And of course you can always generate NSData from the getBytes method.
Cheers,
Hendrik
If you already have your ALAsset, you should be able to get an NSData of the default representation using the following:
NSData *data = [NSData dataWithContentsOfURL:[[asset defaultRepresentation] url]];
I'm try to allow users to pull images out of their Photos collections using ALAssetsLibrary. Users can then upload these images. My goal is to allow users to upload any GIFs they may have in their library w/o loosing any animation they may have.
For PNG and JPEG files I can grab the ALAssetRepresentation, use - (CGImageRef)fullResolutionImage to get a CGImageRef, and then save it to NSData using UIImageJPEGRepresentation or UIImagePNGRepresentation.
However, because no similar function exists for GIF files, all I can do is covert the GIF to either JPEG or PNG, but then I lose the animation.
Is there either
a way to grab the NSData straight from an ALAssetRepresentation object or
a way to go from ALAssetRepresentation -> CGImageRef -> NSData without loosing any gif animation frames?
Thanks in advance!
Yes, there is a quite simple way:
Use the getBytes:fromOffset:length:error: method of ALAssetRepresentation. This gives youthe raw file data of the ALAsset, in your case the GIF file.
What's the best way to save and retrieve an array of images across app restarts?
I'm implementing a caching feature for offline viewing of downloaded images and just want to make sure I'm using the right persisting methods.
Thanks!
The quickest & probably best solution would be to persist your images to disk, no question about it.
You could do something like this to save them as JPEG.
NSData *data = UIImageJPEGRepresentation(image, 1.0f);
[data writeToFile:imagePath atomically:YES];
I am coding an iPhone application where images are transferred from one iPhone to another using Bluetooth. How do I archive an image and send it to another iPhone, then un-archive the image back? Archiving the image directly using NSKeyedarchiver doesn't work.
You can turn UIImage objects into NSData representations using the Image Manipulation function UIImageJPEGRepresentation or UIImagePNGRepresentation.
You can turn the NSData representation into a UIImage using the UIImage convenience method imageWithData: or initializer initWithData:.