Is it possible to lower the resolution of already taken videos/pictures? I need to export low resolution videos/pictures.
U can use "scale" for it, i.e.: 0.5 for half-size
UIImage *ret = nil;
ALAsset *asset =[_assetImages objectAtIndex:page];
ALAssetRepresentation *defaultRep = [asset defaultRepresentation];
ret = [UIImage imageWithCGImage:[defaultRep fullScreenImage] scale:0.5 orientation:0];
You should also look at Joshua Sullivan's answere on:
How to compress/resize image on iPhone OS SDK before uploading to a server?
This changes the reported size of the scaled image, but does not actually change the image data. The data length of the NSData generated on the original and the scaled image is virtually identical.
Related
I am trying to implement a Coverflow ( iCarousel ) with AsyncImageView ( https://github.com/nicklockwood/AsyncImageView ) as cover. It works well with images of size upto 4 MB. But the app crashes when trying to load images of size more than 10 MB. My question is -
1 ) Can i load a image of size 10 MB without tiling ? Since the source of image is from device camera, is it possible to tile those images and then load those images. If so can you share some ideas/code blocks on tiling a large image ?
P.s : I have tried compressing the images, by using UIImageJPEGRepresentation(image,scale), although the image size got reduced from 10 MB to 100 KB, but when i try to load the compressed images, memory issues shows up again. (Looks like iOS decompresses to some extent)
You are confused with the dimensions of the image and its size on disk.
In memory an image take WIDTH*HEIGHT*4 pixels, so let's say your image is 1000x1000px you end up using 4Mb ram.
UIImageJPEGRepresentation save the image with a compression factor, so you end up with a smaller image on disk, but the image has still the same dimensions.
To solve your problem you need to scale the image you downloaded to the correct dimension for your coverflow item.
You can do this using ImageIO framework :
Create a CGImageSource from the downloaded data
Call CGImageSourceCreateThumbnailAtIndex with the 2 properties kCGImageSourceCreateThumbnailFromImageIfAbsent and kCGImageSourceThumbnailMaxPixelSize
Here is the working code
UIImage *result = nil;
if ([data length]) { // NSData of the image
CGImageSourceRef sourceRef = CGImageSourceCreateWithData((CFDataRef)data, nil);
NSMutableDictionary *options = [NSMutableDictionary dictionary];
[options setObject:(id)kCFBooleanTrue forKey:(id)kCGImageSourceCreateThumbnailFromImageIfAbsent];
[options setObject:[NSNumber numberWithInt:400] forKey:(id)kCGImageSourceThumbnailMaxPixelSize];
CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(sourceRef, 0, (CFDictionaryRef)options);
if (imageRef) {
result = [UIImage imageWithCGImage:imageRef]; //Resulting image
CGImageRelease(imageRef);
}
if (sourceRef) CFRelease(sourceRef);
I parsed the data from a web which also contains jpg image. The problem is that the image looks blurry/pixelated on retina display. Any solution for this? Thanks.
NSData *data = [NSData dataWithContentsOfURL:linkUrl];
UIImage *img = [[UIImage alloc] initWithData:data];
// detailViewController.faces.contentScaleFactor=[UIScreen mainScreen].scale;//Attampt to solve the problem
detailViewController.faces.image=img;
After initializing your image with the data, create a new one from it with the correct scale like this:
img = [UIImage imageWithCGImage:img.CGImage scale:[UIScreen mainScreen].scale orientation:img.imageOrientation];
...but note that the image will now appear half the size on retina displays unless you scale it up, for example by stretching it in an image view.
I m taking images from photo library.I have large images of 4-5 mb but i want to compress those images.As i need to store those images in local memory of iphone.for using less memory or for getting less memory warning i need to compress those images.
I don't know how to compress images and videos.So i want to know hot to compress images?
UIImage *image = [info objectForKey:#"UIImagePickerControllerOriginalImage"];
NSData* data = UIImageJPEGRepresentation(image,1.0);
NSLog(#"found an image");
NSString *path = [destinationPath stringByAppendingPathComponent:[NSString stringWithFormat:#"%#.jpeg", name]];
[data writeToFile:path atomically:YES];
This is the code for saving my image. I dont want to store the whole image as its too big. So, I want to compress it to a much smaller size as I'll need to attach multiple images.
Thanks for the reply.
You can choose a lower quality for JPEG encoding
NSData* data = UIImageJPEGRepresentation(image, 0.8);
Something like 0.8 shouldn't be too noticeable, and should really improve file sizes.
On top of this, look into resizing the image before making the JPEG representation, using a method like this:
+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
UIGraphicsBeginImageContext(newSize);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
Source: The simplest way to resize an UIImage?
UIImageJPEGRepresentation(UIImage,Quality);
1.0 means maximum Quality and 0 means minimum quality.
SO change the quality parameter in below line to reduce file size of the image
NSData* data = UIImageJPEGRepresentation(image,1.0);
NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);
OR
NSData *image_Data=UIImageJPEGRepresentation(image_Name,compressionQuality);
return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compressionQuality is 0(most) & 1(least).
I current have an app that uses ALAsssetsLibrary to fetch the photos. I have placed the photo to an image view and I am able to upload to the server. When I tested on the real device after taking some photos, I found out the photos that supposed to be taken in Portrait become a landscape.
Therefore, I called different function to get the CGImage like this:
UIImage *image = [UIImage imageWithCGImage:[representation fullResolutionImage] scale:1.0 orientation:(UIImageOrientation)[representation orientation]];
The first tried out, I used this :
UIImage *image = [UIImage imageWithCGImage:[representation fullResolutionImage]]
I thought the one with scale and orientation could give me the right orientation that the photo was taken. But it didn't give me the right solution.
Do I miss anything that is necessary to generate a correct orientation of photo?
The correct orientation handling depends on the iOS version you are using.
On iOS4 and iOS 5 the thumbnail is already correctly rotated, so you can initialize your UIImage without specifying any rotation parameters.
However for the fullScreenImage, the behavior is different for each iOS version. On iOS 5 the image is already rotated on iOS 4 not.
So on iOS4 you should use:
ALAssetRepresentation *defaultRep = [asset defaultRepresentation];
UIImage *_image = [UIImage imageWithCGImage:[defaultRep fullScreenImage]
scale:[defaultRep scale] orientation:(UIImageOrientation)[defaultRep orientation]];
On iOS5 the following code should work correctly:
ALAssetRepresentation *defaultRep = [asset defaultRepresentation];
UIImage *_image = [UIImage imageWithCGImage:[defaultRep fullScreenImage] scale:[defaultRep scale] orientation:0];
Cheers,
Hendrik
Try this code:-
UIImage* img = [UIImage imageWithCGImage:asset.thumbnail];
img = [UIImage imageWithCGImage:img.CGImage scale:1.0 orientation:UIImageOrientationUp];
This may help you.
My experience is limited to IOS 5.x but I can tell you that the thumbnail and fullscreen images are oriented properly. It's the fullresolutionimage that's horizontal when shot vertically. My solution is to use a category on uiimage that I got from here:
http://www.catamount.com/forums/viewtopic.php?f=21&t=967&start=0
It provides a nice rotating method on a UIImage like this:
UIImage *tmp = [UIImage imageWithCGImage:startingFullResolutionImage];
startingFullResolutionImage = [[tmp imageRotatedByDegrees:-90.0f] CGImage];
For fullResolutionImage, I'd like to provide a solution as follows,
ALAssetRepresentation *rep = [asset defaultRepresentation];
// First, write orientation to UIImage, i.e., EXIF message.
UIImage *image = [UIImage imageWithCGImage:[rep fullResolutionImage] scale:rep.scale orientation:(UIImageOrientation)rep.orientation];
// Second, fix orientation, and drop out EXIF
if (image.imageOrientation != UIImageOrientationUp) {
UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);
[image drawInRect:(CGRect){0, 0, image.size}];
UIImage *normalizedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
image = normalizedImage;
}
// Third, compression
NSData *imageData = UIImageJPEGRepresentation(image, 1.0);
imageData is what you want, and just upload it to your photo server.
By the way, if you think EXIF is useful, you can complement it to normalizedImage as you wish.
I have a tableview, and i am loading images to it. I have images which are ranging from 150kb - 2MB. Since this is too much for a tableview to handle (it takes long time to load, and makes the scrolling slow), i thought of using ImageIO framework to create thumbnail images of images.
I found a code that does this, but i can't undestand it.
1.) Can someone please explain me the code
2.) My problem is that, I have a tableview and i need to load thumbnail images to it. So how can i use the following code and display it on my tableview. Can someone show me some sample code or a tutorial that does this ?
heres the code ;
-(void)buildGallery
{
for (NSUInteger i = 0; i < kMaxPictures; i++)
{
NSInteger imgTag = i + 1;
NYXPictureView* v = [[NYXPictureView alloc] initWithFrame:(CGRect){.origin.x = x, .origin.y = y, .size = _thumbSize}];
NSString* imgPath = [[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:#"%d", imgTag] ofType:#"jpg"];
CGImageSourceRef src = CGImageSourceCreateWithURL((CFURLRef)[NSURL fileURLWithPath:imgPath], NULL);
CFDictionaryRef options = (CFDictionaryRef)[[NSDictionary alloc] initWithObjectsAndKeys:(id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailWithTransform, (id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailFromImageIfAbsent, (id)[NSNumber numberWithDouble:_maxSize], (id)kCGImageSourceThumbnailMaxPixelSize, nil];
CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, options); // Create scaled image
CFRelease(options);
CFRelease(src);
UIImage* img = [[UIImage alloc] initWithCGImage:thumbnail];
[v setImage:img];
[img release];
CGImageRelease(thumbnail);
}
}
Basically the problem you have is due to the fact that when you scale down an image, the number of bytes stored in memory doesnt change when you scale it down. The hardware still has to read your 2mb image, and then render it to a smaller scale. What you need to do is to either change the size of your image (use photoshop or other) or the way im suggesting is to compress your image, and then scale it down. The image will look rough at normal size, but will look ok when you scale it down to a thumbview.
To generate an NSData version of your image encoded as a PNG.
NSData *PNGFile = UIImagePNGRepresentation(myImage);
Or a JPEG, with a quality value set
NSData *JPEGFile = UIImageJPEGRepresentation(myImage, 0.9f);
Both of these will give you an image smaller than you currently have, which will be easier to render in the tableView.
In order to get better performance you're going to have to load the image in a background thread, and after it's in memory add the UIImage to the image view on the main thread. There are a couple ways to go about doing this, but the simplest is going to be using GCD's block based methods.
Resizing the image is definitely still important for memory considerations, but get the asynchronous image loading part down first.