Wednesday, February 23, 2011

iPhone : Resizing image and maintain aspect ratio

Issue : While scaling an image to fit to an image view [CGRect ....],Image was distorting.
Reason: Image stretches/compress itself to fit to specified area and usually get distorted.
So in order to maintain the actual aspect ratio of the image We can use this:

In Header file, Declare a method:

-(UIImage *)resizeImage:(UIImage *)image withWidth:(int) width withHeight:(int) height;

In (implementation).m file :
We need to define radians macro,this will be used in function definition declared above.

static inline double radians (double degrees) {return degrees * M_PI/180;}

Function definition:

-(UIImage *)resizeImage:(UIImage *)image withWidth:(int) width withHeight:(int) height {

CGImageRef imageRef = [image CGImage];
CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);
CGColorSpaceRef colorSpaceInfo = CGColorSpaceCreateDeviceRGB();

if (alphaInfo == kCGImageAlphaNone)
alphaInfo = kCGImageAlphaNoneSkipLast;

CGContextRef bitmap;

if (image.imageOrientation == UIImageOrientationUp | image.imageOrientation == UIImageOrientationDown) {
bitmap = CGBitmapContextCreate(NULL, width, height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, alphaInfo);

} else {
bitmap = CGBitmapContextCreate(NULL, height, width, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, alphaInfo);


if (image.imageOrientation == UIImageOrientationLeft) {
NSLog(@"image orientation left");
CGContextRotateCTM (bitmap, radians(90));
CGContextTranslateCTM (bitmap, 0, -height);

} else if (image.imageOrientation == UIImageOrientationRight) {
NSLog(@"image orientation right");
CGContextRotateCTM (bitmap, radians(-90));
CGContextTranslateCTM (bitmap, -width, 0);

} else if (image.imageOrientation == UIImageOrientationUp) {
NSLog(@"image orientation up");

} else if (image.imageOrientation == UIImageOrientationDown) {
NSLog(@"image orientation down");
CGContextTranslateCTM (bitmap, width,height);
CGContextRotateCTM (bitmap, radians(-180.));


CGContextDrawImage(bitmap, CGRectMake(0, 0, width, height), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage *result = [UIImage imageWithCGImage:ref];


return result;


  1. I used this code. But i think there is still some distortion. I need image of size 98x98. So i pass height:98 and width:98 in the resize function. Do you think i am doing anything wrong? Please help.

  2. @ Nirali,

    You might not be having the image of equal width and height, In case you want to get the image to be scaled to 98X98 (square shape) , your original image should have equal width and height (square shape i.e. equal width and height).

    As we are scaling here..

    Hope this help..

  3. no working giving radian reated error

    1. did you defined this macro (as I mentioned in the post)?

      static inline double radians (double degrees) {return degrees * M_PI/180;}