Asked  6 Months ago    Answers:  5   Viewed   35 times

I have a UIImage that is UIImageOrientationUp (portrait) that I would like to rotate counter-clockwise by 90 degrees (to landscape). I don't want to use a CGAffineTransform. I want the pixels of the UIImage to actually shift position. I am using a block of code (shown below) originally intended to resize a UIImage to do this. I set a target size as the current size of the UIImage but I get an error:

(Error): CGBitmapContextCreate: invalid data bytes/row: should be at least 1708 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedLast.

(I don't get an error whenever I provide a SMALLER size as the target size BTW). How can I ROTATE my UIImage 90 degrees CCW using just core graphics functions while preserving the current size?

    UIImage* sourceImage = anImage; 
    CGFloat targetWidth = targetSize.height;
    CGFloat targetHeight = targetSize.width;

    CGImageRef imageRef = [sourceImage CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

    if (bitmapInfo == kCGImageAlphaNone) {
        bitmapInfo = kCGImageAlphaNoneSkipLast;

    CGContextRef bitmap;

    if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
        bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    } else {

        bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);


    if (sourceImage.imageOrientation == UIImageOrientationRight) {
        CGContextRotateCTM (bitmap, radians(90));
        CGContextTranslateCTM (bitmap, 0, -targetHeight);

    } else if (sourceImage.imageOrientation == UIImageOrientationLeft) {
        CGContextRotateCTM (bitmap, radians(-90));
        CGContextTranslateCTM (bitmap, -targetWidth, 0);

    } else if (sourceImage.imageOrientation == UIImageOrientationDown) {
        // NOTHING
    } else if (sourceImage.imageOrientation == UIImageOrientationUp) {
        CGContextRotateCTM (bitmap, radians(90));
        CGContextTranslateCTM (bitmap, 0, -targetHeight);

    CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];


    return newImage; 



What about something like:

static inline double radians (double degrees) {return degrees * M_PI/180;}
UIImage* rotate(UIImage* src, UIImageOrientation orientation)

    CGContextRef context = UIGraphicsGetCurrentContext();

    if (orientation == UIImageOrientationRight) {
        CGContextRotateCTM (context, radians(90));
    } else if (orientation == UIImageOrientationLeft) {
        CGContextRotateCTM (context, radians(-90));
    } else if (orientation == UIImageOrientationDown) {
        // NOTHING
    } else if (orientation == UIImageOrientationUp) {
        CGContextRotateCTM (context, radians(90));

    [src drawAtPoint:CGPointMake(0, 0)];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    return image;
Tuesday, June 1, 2021
answered 6 Months ago

You need CSS to achieve this, e.g.:

#container_2 {
    -webkit-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    -o-transform: rotate(90deg);
    -ms-transform: rotate(90deg);
    transform: rotate(90deg);


#container_2 {
  width: 100px;
  height: 100px;
  border: 1px solid red;
  -webkit-transform: rotate(45deg);
  -moz-transform: rotate(45deg);
  -o-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
<div id="container_2"></div>

(There's 45 degrees rotation in the demo, so you can see the effect)

Note: The -o- and -moz- prefixes are no longer relevant and probably not required. IE9 requires -ms- and Safari and the Android browser require -webkit-

Update 2018: Vendor prefixes are not needed anymore. Only transform is sufficient. (thanks @rinogo)

Saturday, June 12, 2021
answered 6 Months ago

let a be an nxn array 0 based indexing

f = floor(n/2)
c = ceil(n/2)

for x = 0 to f - 1
  for y = 0 to c - 1
    temp = a[x,y]
    a[x,y] = a[y,n-1-x]
    a[y,n-1-x] = a[n-1-x,n-1-y]
    a[n-1-x,n-1-y] = a[n-1-y,x]
    a[n-1-y,x] = temp

Edit If you want to avoid using temp, this works (it also rotates in the correct direction) this time in python.

def rot2(a):
  n = len(a)
  c = (n+1) / 2
  f = n / 2
  for x in range(c):
    for y in range(f):
      a[x][y] = a[x][y] ^ a[n-1-y][x]
      a[n-1-y][x] = a[x][y] ^ a[n-1-y][x]
      a[x][y] = a[x][y] ^ a[n-1-y][x]

      a[n-1-y][x] = a[n-1-y][x] ^ a[n-1-x][n-1-y]
      a[n-1-x][n-1-y] = a[n-1-y][x] ^ a[n-1-x][n-1-y]
      a[n-1-y][x] = a[n-1-y][x] ^ a[n-1-x][n-1-y]

      a[n-1-x][n-1-y] = a[n-1-x][n-1-y]^a[y][n-1-x]
      a[y][n-1-x] = a[n-1-x][n-1-y]^a[y][n-1-x]
      a[n-1-x][n-1-y] = a[n-1-x][n-1-y]^a[y][n-1-x]

Note: This only works for matrices of integers.

Tuesday, July 27, 2021
answered 4 Months ago

I believe it is an iOS 8 bug. For example if you open your contacts app and click edit/add photo/take photo, the same issue occurs on a standard iOS app! Post the issue to Apple support just as I have.

Tuesday, July 27, 2021
answered 4 Months ago

that question seems to be a lack-of-imagination issue only.

here is a quick solution for the problem:

in the Interface Builder, you need to add a container view and that view holds the avatar image view; it is the raw picture of how it look on my screen the view in the editor:

in the interface builder

that is the relationship between the two views in the view hiearchy: the container view is the superview of the avatar image view:

the hie

after adding the related outlets (call them _containerView and _avatarImageView) to the class and conntected them to the views; we also can add this little snippet to our code:

[_containerView setBackgroundColor:[UIColor clearColor]];
[_containerView.layer setCornerRadius:MIN(_containerView.bounds.size.width, _containerView.bounds.size.height) / 2.0];
[_containerView.layer setBorderColor:[[UIColor whiteColor] CGColor]];
[_containerView.layer setBorderWidth:4.0];

[_avatarImageView.layer setCornerRadius:MIN(_avatarImageView.bounds.size.width, _avatarImageView.bounds.size.height) / 2.0];
[_avatarImageView.layer setMasksToBounds:TRUE];

and after running the project on the simulator or a real device, violá, the transparent ring appears between the image and the border:

the transparent ring appears

NOTE: the actual size of the transparent ring depends on how much smaller the avatar than the container view, which holds it. Important! I do not know who the girl is, please don't ask me about her phone number.

Friday, August 20, 2021
answered 4 Months ago
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