// 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

// 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

转自UIImage rotation and scaling