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iPhone: UIImage rotation and mirroring
http://www.platinumball.net/blog/2009/03/30/iphone-uiimage-rotation-and-mirroring/
Update: This post has been superseded. Please go read this instead:UIImage rotation and scaling.
My access logs show that you webbernauts like my iPhone articles better than anything else on this site. Very well then, here’s another one.
I recently found myself with a need to rotate the contents of a UIImage 90 degrees to the right or left and then display it. Apparently this is easy if your image is inside a UIImageView and you’re willing to rotate the whole view, but that’s not what I have in mind. Rotating the UIImage itself turns out to be pretty danged complicated, and requires a great deal of math. I suck at math.
Fortunately for me, the code given in this guy’s blog post tackles 95 percent of the problem, and 100 percent of the math. Heh! It’s not quitewhat I want, however. The function given in that blog post queries the EXIF data inside the image and rotates it based on that. I want the method’s caller to be able to specify what type of rotation should be done. I tinkered with the code for awhile and got exactly what I wanted.
The original blog post’s code was written as a standalone C function. I wrote my version as a category attached to UIImage. Say you’ve got a UIImage you want to rotate 90 degrees left. It’s done like this:
newImage = [oldImage rotate:UIImageOrientationLeft];
newImage
will be a newly-created copy of oldImage
, rotated 90 degrees left. Other options include UIImageOrientationRight
,UIImageOrientationDown
(for a new image that’s an upside-down copy of the original), and so on. There are also “mirrored” variants, which both rotate the image and mirror its contents left-to-right.
In the process of getting it to work the way I wanted, I made a bunch of changes to the code. I reformatted it so that the lines are no longer than 78 characters. (One of these days I’m going to write a blog post about why I think that’s a good thing.) The original function had two or more unnecessary copies of some data and superfluous calls to external functions, which I eliminated. The old code trimmed the size of the original image if it was bigger than a certain size, which I eliminated. The original had several copies of an identical clause for swapping the width and height of a CGRect, which I refactored into a separate helper function. There are other changes as well, but I’ll spare you the details.
Okay, one more change that I’m going to document. I am 85 percent sure that the original code has a bug. It does not work properly when the input orientation is UIImageOrientationLeftMirrored
orUIImageOrientationRightMirrored
. The new image gets partially chopped off along one edge, which I fixed. It could be that it was not a bug in the context where the original code was being used, but it definitely is in this new context. I’ve tested all orientations in the iPhone simulator, and they all work.
First, here’s UKImage.h, which defines the category.
/ UKImage.h -- extra UIImage methods
// by allen brunson march 29 2009
#ifndef UKIMAGE_H
#define UKIMAGE_H
#import <UIKit/UIKit.h>
@interface UIImage (UKImage)-(UIImage*)rotate:(UIImageOrientation)orient;
@end
#endif // UKIMAGE_H
Now here’s UKImage.mm, which defines the rotate:
method. You can rename this file to UKImage.m if you never use any C++ constructs in your code.
// UKImage.mm -- extra UIImage methods
// by allen brunson march 29 2009
// based on original code by Kevin Lohman:
// http://blog.logichigh.com/2008/06/05/uiimage-fix/
#include "UKImage.h"
static CGRect swapWidthAndHeight(CGRect rect)
{
CGFloat swap = rect.size.width;
rect.size.width = rect.size.height;
rect.size.height = swap;
return rect;
}
@implementation UIImage (UKImage)
-(UIImage*)rotate:(UIImageOrientation)orient
{
CGRect bnds = CGRectZero;
UIImage* copy = nil;
CGContextRef ctxt = nil;
CGImageRef imag = self.CGImage;
CGRect rect = CGRectZero;
CGAffineTransform tran = CGAffineTransformIdentity;
rect.size.width = CGImageGetWidth(imag);
rect.size.height = CGImageGetHeight(imag);
bnds = rect;
switch (orient)
{
case UIImageOrientationUp:
// would get you an exact copy of the original
assert(false);
return nil;
case UIImageOrientationUpMirrored:
tran = CGAffineTransformMakeTranslation(rect.size.width, 0.0);
tran = CGAffineTransformScale(tran, -1.0, 1.0);
break;
case UIImageOrientationDown:
tran = CGAffineTransformMakeTranslation(rect.size.width,
rect.size.height);
tran = CGAffineTransformRotate(tran, M_PI);
break;
case UIImageOrientationDownMirrored:
tran = CGAffineTransformMakeTranslation(0.0, rect.size.height);
tran = CGAffineTransformScale(tran, 1.0, -1.0);
break;
case UIImageOrientationLeft:
bnds = swapWidthAndHeight(bnds);
tran = CGAffineTransformMakeTranslation(0.0, rect.size.width);
tran = CGAffineTransformRotate(tran, 3.0 * M_PI / 2.0);
break;
case UIImageOrientationLeftMirrored:
bnds = swapWidthAndHeight(bnds);
tran = CGAffineTransformMakeTranslation(rect.size.height,
rect.size.width);
tran = CGAffineTransformScale(tran, -1.0, 1.0);
tran = CGAffineTransformRotate(tran, 3.0 * M_PI / 2.0);
break;
case UIImageOrientationRight:
bnds = swapWidthAndHeight(bnds);
tran = CGAffineTransformMakeTranslation(rect.size.height, 0.0);
tran = CGAffineTransformRotate(tran, M_PI / 2.0);
break;
case UIImageOrientationRightMirrored:
bnds = swapWidthAndHeight(bnds);
tran = CGAffineTransformMakeScale(-1.0, 1.0);
tran = CGAffineTransformRotate(tran, M_PI / 2.0);
break;
default:
// orientation value supplied is invalid
assert(false);
return nil;
}
UIGraphicsBeginImageContext(bnds.size);
ctxt = UIGraphicsGetCurrentContext();
switch (orient)
{
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
CGContextScaleCTM(ctxt, -1.0, 1.0);
CGContextTranslateCTM(ctxt, -rect.size.height, 0.0);
break;
default:
CGContextScaleCTM(ctxt, 1.0, -1.0);
CGContextTranslateCTM(ctxt, 0.0, -rect.size.height);
break;
}
CGContextConcatCTM(ctxt, tran);
CGContextDrawImage(UIGraphicsGetCurrentContext(), rect, imag);
copy = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return copy;
}
@end
iPhone: UIImage rotation and scaling
http://www.platinumball.net/blog/2010/01/31/iphone-uiimage-rotation-and-scaling/
January 31, 2010 8:03 pm
Hello to my three remaining blog subscribers! Long time no see!
For my first post back after my long hiatus, I’m going to revisit the single most popular entry I’ve written to date, which was about UIImage rotation. I’ve used that code a great deal since I first wrote it. I’ve modified it several times. It’s pretty near perfect at this point.
The original code I modified for that earlier post was for dealing with photos taken with the iPhone camera. I stripped out a lot of that stuff, because I was only interested in rotating images that were embedded in the program. And then, wouldn’t you know it, I got a contract job that required me to deal with iPhone camera images as well. So I had to revisit the subject.
The original code from blog.logichigh.com had the rotation and scaling all lumped together in one chaotic function. I split it out into separate rotation and scaling methods, so they can be used independently. It also makes for easier code maintenance.
The code contains [UIImage rotate:]
, which works the same as the last time around, but it has been streamlined a bit internally. It will rotate anyUIImage
to any orientation, with or without mirroring. Then we have two scaling methods, the simplest being [UIImage scaleWithMaxSize:]
. You provide it with a float value, which is the largest width and/or height that you want the output image to have. If the input image is already smaller than that, it won’t be scaled.
Finally, the all-singing, all-dancing method for massaging photos from the iPhone camera: [UIImage rotateAndScaleFromCameraWithMaxSize:]
. It examines the EXIF data in the image and, if needed, rotates it to the proper orientation. Then it scales the image to the maximum width and/or height supplied to the method.
This code has been thoroughly tested in several real-world iPhone projects. There are no known bugs. If you find one, I’d love to hear about it, so I can fix it.
// WBImage.h -- extra UIImage methods
// by allen brunson march 29 2009
#ifndef WBIMAGE_H
#define WBIMAGE_H
#import <UIKit/UIKit.h>
@interface UIImage (WBImage)
// rotate UIImage to any angle
-(UIImage*)rotate:(UIImageOrientation)orient;
// rotate and scale image from iphone camera
-(UIImage*)rotateAndScaleFromCameraWithMaxSize:(CGFloat)maxSize;
// scale this image to a given maximum width and height
-(UIImage*)scaleWithMaxSize:(CGFloat)maxSize;
-(UIImage*)scaleWithMaxSize:(CGFloat)maxSize
quality:(CGInterpolationQuality)quality;
@end
#endif // WBIMAGE_H
And here’s the implementation file, WBImage.mm:
// WBImage.mm -- extra UIImage methods
// by allen brunson march 29 2009
#include "WBImage.h"
static inline CGFloat degreesToRadians(CGFloat degrees)
{
return M_PI * (degrees / 180.0);
}
static inline CGSize swapWidthAndHeight(CGSize size)
{
CGFloat swap = size.width;
size.width = size.height;
size.height = swap;
return size;
}
@implementation UIImage (WBImage)
// rotate an image to any 90-degree orientation, with or without mirroring.
// original code by kevin lohman, heavily modified by yours truly.
// http://blog.logichigh.com/2008/06/05/uiimage-fix/
-(UIImage*)rotate:(UIImageOrientation)orient
{
CGRect bnds = CGRectZero;
UIImage* copy = nil;
CGContextRef ctxt = nil;
CGRect rect = CGRectZero;
CGAffineTransform tran = CGAffineTransformIdentity;
bnds.size = self.size;
rect.size = self.size;
switch (orient)
{
case UIImageOrientationUp:
return self;
case UIImageOrientationUpMirrored:
tran = CGAffineTransformMakeTranslation(rect.size.width, 0.0);
tran = CGAffineTransformScale(tran, -1.0, 1.0);
break;
case UIImageOrientationDown:
tran = CGAffineTransformMakeTranslation(rect.size.width,
rect.size.height);
tran = CGAffineTransformRotate(tran, degreesToRadians(180.0));
break;
case UIImageOrientationDownMirrored:
tran = CGAffineTransformMakeTranslation(0.0, rect.size.height);
tran = CGAffineTransformScale(tran, 1.0, -1.0);
break;
case UIImageOrientationLeft:
bnds.size = swapWidthAndHeight(bnds.size);
tran = CGAffineTransformMakeTranslation(0.0, rect.size.width);
tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
break;
case UIImageOrientationLeftMirrored:
bnds.size = swapWidthAndHeight(bnds.size);
tran = CGAffineTransformMakeTranslation(rect.size.height,
rect.size.width);
tran = CGAffineTransformScale(tran, -1.0, 1.0);
tran = CGAffineTransformRotate(tran, degreesToRadians(-90.0));
break;
case UIImageOrientationRight:
bnds.size = swapWidthAndHeight(bnds.size);
tran = CGAffineTransformMakeTranslation(rect.size.height, 0.0);
tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
break;
case UIImageOrientationRightMirrored:
bnds.size = swapWidthAndHeight(bnds.size);
tran = CGAffineTransformMakeScale(-1.0, 1.0);
tran = CGAffineTransformRotate(tran, degreesToRadians(90.0));
break;
default:
// orientation value supplied is invalid
assert(false);
return nil;
}
UIGraphicsBeginImageContext(bnds.size);
ctxt = UIGraphicsGetCurrentContext();
switch (orient)
{
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
CGContextScaleCTM(ctxt, -1.0, 1.0);
CGContextTranslateCTM(ctxt, -rect.size.height, 0.0);
break;
default:
CGContextScaleCTM(ctxt, 1.0, -1.0);
CGContextTranslateCTM(ctxt, 0.0, -rect.size.height);
break;
}
CGContextConcatCTM(ctxt, tran);
CGContextDrawImage(ctxt, rect, self.CGImage);
copy = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return copy;
}
-(UIImage*)rotateAndScaleFromCameraWithMaxSize:(CGFloat)maxSize
{
UIImage* imag = self;
imag = [imag rotate:imag.imageOrientation];
imag = [imag scaleWithMaxSize:maxSize];
return imag;
}
-(UIImage*)scaleWithMaxSize:(CGFloat)maxSize
{
return [self scaleWithMaxSize:maxSize quality:kCGInterpolationHigh];
}
-(UIImage*)scaleWithMaxSize:(CGFloat)maxSize
quality:(CGInterpolationQuality)quality
{
CGRect bnds = CGRectZero;
UIImage* copy = nil;
CGContextRef ctxt = nil;
CGRect orig = CGRectZero;
CGFloat rtio = 0.0;
CGFloat scal = 1.0;
bnds.size = self.size;
orig.size = self.size;
rtio = orig.size.width / orig.size.height;
if ((orig.size.width <= maxSize) && (orig.size.height <= maxSize))
{
return self;
}
if (rtio > 1.0)
{
bnds.size.width = maxSize;
bnds.size.height = maxSize / rtio;
}
else
{
bnds.size.width = maxSize * rtio;
bnds.size.height = maxSize;
}
UIGraphicsBeginImageContext(bnds.size);
ctxt = UIGraphicsGetCurrentContext();
scal = bnds.size.width / orig.size.width;
CGContextSetInterpolationQuality(ctxt, quality);
CGContextScaleCTM(ctxt, scal, -scal);
CGContextTranslateCTM(ctxt, 0.0, -orig.size.height);
CGContextDrawImage(ctxt, orig, self.CGImage);
copy = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return copy;
}
@end
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