Brilliant. Simple and neat solution to a vexing problem. I guess they left the resizing out because most of the time you’ll be using UIImageView, which handles the scaling for you. Unfortunately, the UIImageView for an image on a UITableViewCell isn’t accessible, so you’re stuffed if you don’t manually resize your image to the correct size.

Thanks !

Actually, you can put UIImageView on a UITableViewCell by putting it as a subview. Nothing wrong with that. Something along:

- (id)initWithFrame:(CGRect)frame reuseIdentifier:(NSString *)reuseIdentifier {
   if (self = [super initWithFrame:frame reuseIdentifier:reuseIdentifier]) {
      UIImageView* imgView = [[UIImageView alloc] initWithFrame:CGMakeRect(0,0,30,frame.size.height)];
      imgView.image = [UIImage imageWithName:@"anImage.png"];
      [self addSubview:[imgView autorelease]];
   }
   return self;
}

Should work out of the box. But what I use my solution for mainly is when taking pictures in the image album and then using them in a CALayer, which cannot take images larger than 1024×1024. Also, managing resources by releasing the original… saves a lot of memory.

The solution is great and seems to be working for everyone. But I’ve got a problem here. I need to save a smaller version of an image to file, so I do the following:

	UIImage *initialImage = [UIImage imageNamed:@"SomeName.jpg"];
 
	UIGraphicsBeginImageContext(CGSizeMake(176.0, 235.0));
	[initialImage drawInRect:CGRectMake(0.0, 0.0, 176.0, 235.0)];
	UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
 
	NSData *jpegData = UIImageJPEGRepresentation(newImage, 0.5);
        [jpegData writeToFile:imagePath atomically:NO];

The file it creates is of the required size, but blank – just a white rectangle. The undocumented method does just the same. I’m totally noob, so my mistake must be painfully stupid, but I’m stuck here. Any ideas what could be wrong?

Thank you!

I’ve just found out that it works when the initial picture is of PNG format, but it makes blank resized images for JPG. Must be some obvious reason, but I just don’t get it.

PS What is the correct tag for quoting code in here?

Hey Thorny,

The right way to put code here is with the <pre lang=”objc”>. For syntax highlighting, you can change the lang parameter. There is also a way to put line numbers in there. I might change the syntax plugin to use a different tag and put something above the textarea in the theme to list the available tags.

I’m gonna try with a JPG and a PNG to see what could be the problem. I’m as much surprised as you are.

very nice, thanks

[...] also made a post here about how to resize images [...]

[...] Image resizing: http://ofcodeandmen.poltras.com/2008/10/30/undocumented-uiimage-resizing/ [...]

If you don’t like undocumented calls, you can just create a new bitmap graphic context, make it the current context, set up the correct affine transform, draw the source into it with CGContextDrawImage(), and tell it to hand you back the UIImage.

If you don’t need the image handed back, then just set the correct affine transform of the current context, and CGContextDrawImage() the source into it

I’m newbie and curious. Will i be responsible for releasing the image received by the created methods?

@GM: the image is autoreleased. Check out UIGraphicsGetImageFromCurrentImageContext() documentation for details.

@DavidPhillipOster: That’s what I do, but I use drawInRect instead of using bitmap+transform. Your method might be faster, but not by much.

Given that this category contains drawing code, you’ll need to make sure you only resize images on the main thread. (I would get EXEC_BAD_ACCESS errors whenever I resized images on a separate thread while running on the device.)

Thanks. Nitpick: I would have named it -imageByScalingToSize: instead of -scaleImageToSize:, following the Cocoa naming convention of hinting what type will be returned.

Thanks for this post!
Has anyone found a solution for scaling JPEG ?

Thank you!!! This works great.

[...] be skewed so cropping was required. All of the examples I found either focused on cropping only or resizing but I couldn’t find any that did [...]

Awesome, thanks for posting this. Just what I needed.

Does anyone know what the “interpolationQuality:” parameter does? And how to replicate that behavior if you implement it yourself? Thanks,

See CGContextSetInterpolationQuality(bitmap, interpolationQuality);

- (UIImage*)imageWithImage:(UIImage*)image
scaledToSize:(CGSize)newSize
iQ:(double)interpolationQuality;
{
UIGraphicsBeginImageContext( newSize );
CGContextSetInterpolationQuality(UIGraphicsGetCurrentContext(), interpolationQuality);
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return newImage;
}