Adding thumbnail size images to tableview - iphone

Question

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);
}
}

Answer 1

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.

Answer 2

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.