UIImage resize (Scale proportion)

Question

Possible Duplicate:
Resize UIImage with aspect ratio?

The following piece of code is resizing the image perfectly, but the problem is that it messes up the aspect ratio (resulting in a skewed image). Any pointers?

// Change image resolution (auto-resize to fit)
+ (UIImage *)scaleImage:(UIImage*)image toResolution:(int)resolution {
    CGImageRef imgRef = [image CGImage];
    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);
    CGRect bounds = CGRectMake(0, 0, width, height);

    //if already at the minimum resolution, return the orginal image, otherwise scale
    if (width <= resolution && height <= resolution) {
        return image;

    } else {
        CGFloat ratio = width/height;

        if (ratio > 1) {
            bounds.size.width = resolution;
            bounds.size.height = bounds.size.width / ratio;
        } else {
            bounds.size.height = resolution;
            bounds.size.width = bounds.size.height * ratio;
        }
    }

    UIGraphicsBeginImageContext(bounds.size);
    [image drawInRect:CGRectMake(0.0, 0.0, bounds.size.width, bounds.size.height)];
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return imageCopy;
}

See this question (and my answer ;): http://stackoverflow.com/questions/1703100/resize-uiimage-with-aspect-ratio/1703210#1703210 — Frank Schmitt, Apr 16 '10 at 21:52
Links to other SO questions aren't really considered great answers. If this is a duplicate, it should be closed as such. — joran, Jul 02 '12 at 04:02
This helped me with an issue where I needed to scale an UIImage, thanks :) — RelativeGames, Mar 19 '13 at 15:45

score 122 · Answer 1 · edited Jan 23 '13 at 10:13

122

I used this single line of code to create a new UIImage which is scaled. Set the scale and orientation params to achieve what you want. The first line of code just grabs the image.

    // grab the original image
    UIImage *originalImage = [UIImage imageNamed:@"myImage.png"];
    // scaling set to 2.0 makes the image 1/2 the size. 
    UIImage *scaledImage = 
                [UIImage imageWithCGImage:[originalImage CGImage] 
                              scale:(originalImage.scale * 2.0)
                                 orientation:(originalImage.imageOrientation)];

edited Jan 23 '13 at 10:13

Ned

1,378
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answered Sep 09 '10 at 18:02

Mark24x7

1,447
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20

This is a logical resize. If you are looking to resize an image for performance purposes have a look at http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/ or even at http://eran.sandler.co.il/2011/11/07/uiimage-in-ios-5-orientation-and-resize/ if you experience a wrong behaviour in iOS 5. – Xavi Gil Nov 22 '11 at 10:06
10

clearly it is Abdul or 36 people wouldn't have up voted. You are doing something wrong. – Adam Waite Nov 06 '13 at 18:05
8

scaling to 2.0 makes the image 1/2 the size...LOL! – zonabi Sep 23 '15 at 21:42
1

for swift: `let img: UIImage = UIImage(named: "lena")!` `var scaledImage = UIImage(CGImage: img.CGImage!, scale: img.scale * 2, orientation: img.imageOrientation)` – vkalit Nov 25 '15 at 19:22
@zonabi, it's not so funny. What about dividing by 2.0 instead of multiplying... `UIImage *scaledImage = [UIImage imageWithCGImage:[image CGImage] scale:image.scale/2.0 orientation:(image.imageOrientation)];` This way you get a more logical presentation of your scale desire (aka "I want to multiply scale with a n factor") – Bejil Dec 04 '15 at 08:38

score 16 · Answer 2 · edited Nov 01 '11 at 22:56

That's ok not a big problem . thing is u got to find the proportional width and height

like if size is 2048.0 x 1360.0 which has to be resized to 320 x 480 resolution then the resulting image size should be 722.0 x 480.0

here is the formulae to do that . if w,h is original and x,y are resulting image.
w/h=x/y 
=> 
x=(w/h)*y;  

submitting w=2048,h=1360,y=480 => x=722.0 ( here width>height. if height>width then consider x to be 320 and calculate y)

U can submit in this web page . ARC

Confused ? alright , here is category for UIImage which will do the thing for you.

@interface UIImage (UIImageFunctions)
    - (UIImage *) scaleToSize: (CGSize)size;
    - (UIImage *) scaleProportionalToSize: (CGSize)size;
@end
@implementation UIImage (UIImageFunctions)

- (UIImage *) scaleToSize: (CGSize)size
{
    // Scalling selected image to targeted size
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, size.width, size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
    CGContextClearRect(context, CGRectMake(0, 0, size.width, size.height));

    if(self.imageOrientation == UIImageOrientationRight)
    {
        CGContextRotateCTM(context, -M_PI_2);
        CGContextTranslateCTM(context, -size.height, 0.0f);
        CGContextDrawImage(context, CGRectMake(0, 0, size.height, size.width), self.CGImage);
    }
    else
        CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), self.CGImage);

    CGImageRef scaledImage=CGBitmapContextCreateImage(context);

    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);

    UIImage *image = [UIImage imageWithCGImage: scaledImage];

    CGImageRelease(scaledImage);

    return image;
}

- (UIImage *) scaleProportionalToSize: (CGSize)size1
{
    if(self.size.width>self.size.height)
    {
        NSLog(@"LandScape");
        size1=CGSizeMake((self.size.width/self.size.height)*size1.height,size1.height);
    }
    else
    {
        NSLog(@"Potrait");
        size1=CGSizeMake(size1.width,(self.size.height/self.size.width)*size1.width);
    }

    return [self scaleToSize:size1];
}

@end

-- the following is appropriate call to do this if img is the UIImage instance.

img=[img scaleProportionalToSize:CGSizeMake(320, 480)];

Do you mean anImageView.contentMode=UIViewContentModeScaleAspectFit;? — Wayne Lo, Mar 04 '11 at 23:37
yup similar to content Mode but not using any UI elements thus scaled image can further be stored into file or db... — RamaKrishna Chunduri, Sep 25 '14 at 10:05

score 5 · Answer 3 · answered Feb 29 '12 at 00:55

This fixes the math to scale to the max size in both width and height rather than just one depending on the width and height of the original.

- (UIImage *) scaleProportionalToSize: (CGSize)size
{
    float widthRatio = size.width/self.size.width;
    float heightRatio = size.height/self.size.height;

    if(widthRatio > heightRatio)
    {
        size=CGSizeMake(self.size.width*heightRatio,self.size.height*heightRatio);
    } else {
        size=CGSizeMake(self.size.width*widthRatio,self.size.height*widthRatio);
    }

    return [self scaleToSize:size];
}

Mustafa · Accepted Answer · 2013-03-26T05:12:30.540

This change worked for me:

// The size returned by CGImageGetWidth(imgRef) & CGImageGetHeight(imgRef) is incorrect as it doesn't respect the image orientation!
// CGImageRef imgRef = [image CGImage];
// CGFloat width = CGImageGetWidth(imgRef);
// CGFloat height = CGImageGetHeight(imgRef);
//
// This returns the actual width and height of the photo (and hence solves the problem
CGFloat width = image.size.width; 
CGFloat height = image.size.height;
CGRect bounds = CGRectMake(0, 0, width, height);

score 0 · Answer 5 · answered Apr 15 '10 at 14:07

Try to make the bounds's size integer.

#include <math.h>
....

    if (ratio > 1) {
        bounds.size.width = resolution;
        bounds.size.height = round(bounds.size.width / ratio);
    } else {
        bounds.size.height = resolution;
        bounds.size.width = round(bounds.size.height * ratio);
    }

UIImage resize (Scale proportion)

5 Answers5

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