The simplest way to resize an UIImage?

In my iPhone app, I take a picture with the camera, then I want to resize it to 290*390 pixels. I was using this method to resize the image :

UIImage *newImage = [image _imageScaledToSize:CGSizeMake(290, 390)
                         interpolationQuality:1];    

It works perfectly, but it's an undocumented function, so I can't use it anymore with iPhone OS4.

So... what is the simplest way to resize an UIImage ?

Solution 1:

The simplest way is to set the frame of your UIImageView and set the contentMode to one of the resizing options.

Or you can use this utility method, if you actually need to resize an image:

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    //UIGraphicsBeginImageContext(newSize);
    // In next line, pass 0.0 to use the current device's pixel scaling factor (and thus account for Retina resolution).
    // Pass 1.0 to force exact pixel size.
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

Example usage:

#import "MYUtil.h"
…
UIImage *myIcon = [MYUtil imageWithImage:myUIImageInstance scaledToSize:CGSizeMake(20, 20)];

Solution 2:

Proper Swift 3.0 for iOS 10+ solution: Using ImageRenderer and closure syntax:

func imageWith(newSize: CGSize) -> UIImage {
    let image = UIGraphicsImageRenderer(size: newSize).image { _ in
        draw(in: CGRect(origin: .zero, size: newSize))
    }
        
    return image.withRenderingMode(renderingMode)
}

And here's the Objective-C version:

@implementation UIImage (ResizeCategory)
- (UIImage *)imageWithSize:(CGSize)newSize
{
    UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc] initWithSize:newSize];
    UIImage *image = [renderer imageWithActions:^(UIGraphicsImageRendererContext*_Nonnull myContext) {
        [self drawInRect:(CGRect) {.origin = CGPointZero, .size = newSize}];
    }];
    return [image imageWithRenderingMode:self.renderingMode];
}
@end