iOS UIImage扩展方法(category):放大、旋转、合并UIImage、增加渐变层、添加阴影、调节透明度、保存到相册

一有用的 UIImage 扩展，支持（等比例）放大和旋转可在许多 App 中使用。
UIImage-Extensions.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

CGFloat DegreesToRadians(CGFloat degrees);
CGFloat RadiansToDegrees(CGFloat radians);

@interface UIImage (JQ_Extensions)
- (UIImage *)imageAtRect:(CGRect)rect;- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize;
- (UIImage *)imageByScalingToSize:(CGSize)targetSize;
- (UIImage *)imageRotatedByRadians:(CGFloat)radians;
- (UIImage *)imageRotatedByDegrees:(CGFloat)degrees;

- (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2;

- (UIImage *) imageWithBackgroundColor:(UIColor *)bgColor
                           shadeAlpha1:(CGFloat)alpha1
                           shadeAlpha2:(CGFloat)alpha2
                           shadeAlpha3:(CGFloat)alpha3
                           shadowColor:(UIColor *)shadowColor
                          shadowOffset:(CGSize)shadowOffset
                            shadowBlur:(CGFloat)shadowBlur;
- (UIImage *)imageWithShadowColor:(UIColor *)shadowColor
                     shadowOffset:(CGSize)shadowOffset
                       shadowBlur:(CGFloat)shadowBlur;

- (UIImage *)imageByApplyingAlpha:(CGFloat)alpha;

- ( void ) saveToAlbumWithMetadata: ( NSDictionary * ) metadata customAlbumName: ( NSString * ) customAlbumName completionBlock: ( void ( ^ )( void )) completionBlock failureBlock: ( void ( ^ )( NSError * error )) failureBlock

@end;

UIImage-Extensions.m

#import "UIImage-Extensions.h"

CGFloat DegreesToRadians(CGFloat degrees) {return degrees * M_PI / 180;};
CGFloat RadiansToDegrees(CGFloat radians) {return radians * 180/M_PI;};

@implementation UIImage (JQ_Extensions)

-(UIImage *)imageAtRect:(CGRect)rect
{
    
    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
    UIImage* subImage = [UIImage imageWithCGImage: imageRef];
    CGImageRelease(imageRef);
    
    return subImage;
    
}
- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {
    
    UIImage *sourceImage = self;
    UIImage *newImage = nil;
    
    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;
    
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
    
    if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
        
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;
        
        if (widthFactor < heightFactor) 
            scaleFactor = widthFactor;
        else
            scaleFactor = heightFactor;
        
        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;
        
        // center the image
        
        if (widthFactor < heightFactor) {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
        } else if (widthFactor > heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
    }
    
    
    // this is actually the interesting part:
    
    UIGraphicsBeginImageContext(targetSize);
    
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    
    [sourceImage drawInRect:thumbnailRect];
    
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    if(newImage == nil) NSLog(@"could not scale image");
    
    
    return newImage ;
}

- (UIImage *)imageByScalingToSize:(CGSize)targetSize {
    
    UIImage *sourceImage = self;
    UIImage *newImage = nil;
    
    //   CGSize imageSize = sourceImage.size;
    //   CGFloat width = imageSize.width;
    //   CGFloat height = imageSize.height;
    
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    
    //   CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
    
    // this is actually the interesting part:
    
    UIGraphicsBeginImageContext(targetSize);
    
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    
    [sourceImage drawInRect:thumbnailRect];
    
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    if(newImage == nil) NSLog(@"could not scale image");
    
    
    return newImage ;
}

- (UIImage *)imageRotatedByRadians:(CGFloat)radians
{
    return [self imageRotatedByDegrees:RadiansToDegrees(radians)];
}

- (UIImage *)imageRotatedByDegrees:(CGFloat)degrees 
{   
    // calculate the size of the rotated view's containing box for our drawing space
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,self.size.width, self.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(DegreesToRadians(degrees));
    rotatedViewBox.transform = t;
    CGSize rotatedSize = rotatedViewBox.frame.size;
    [rotatedViewBox release];
    
    // Create the bitmap context
    UIGraphicsBeginImageContext(rotatedSize);
    CGContextRef bitmap = UIGraphicsGetCurrentContext();
    
    // Move the origin to the middle of the image so we will rotate and scale around the center.
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);
    
    //   // Rotate the image context
    CGContextRotateCTM(bitmap, DegreesToRadians(degrees));
    
    // Now, draw the rotated/scaled image into the context
    CGContextScaleCTM(bitmap, 1.0, -1.0);
    CGContextDrawImage(bitmap, CGRectMake(-self.size.width / 2, -self.size.height / 2, self.size.width, self.size.height), [self CGImage]);
    
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
    
}

// Combine two UIImages

- (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2 {
    UIGraphicsBeginImageContext(image2.size);
    
    // Draw image1
    [image1 drawInRect:CGRectMake(0, 0, image1.size.width, image1.size.height)];
    
    // Draw image2
    [image2 drawInRect:CGRectMake(0, 0, image2.size.width, image2.size.height)];
    
    UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return resultingImage;
}

- (UIImage *) imageWithBackgroundColor:(UIColor *)bgColor
                           shadeAlpha1:(CGFloat)alpha1
                           shadeAlpha2:(CGFloat)alpha2
                           shadeAlpha3:(CGFloat)alpha3
                           shadowColor:(UIColor *)shadowColor
                          shadowOffset:(CGSize)shadowOffset
                            shadowBlur:(CGFloat)shadowBlur {
    UIImage *image = self;
    CGColorRef cgColor = [bgColor CGColor];
    CGColorRef cgShadowColor = [shadowColor CGColor];
    CGFloat components[16] = {1,1,1,alpha1,1,1,1,alpha1,1,1,1,alpha2,1,1,1,alpha3};
    CGFloat locations[4] = {0,0.5,0.6,1};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef colorGradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, (size_t)4);
    CGRect contextRect;
    contextRect.origin.x = 0.0f;
    contextRect.origin.y = 0.0f;
    contextRect.size = [image size];
    //contextRect.size = CGSizeMake([image size].width+5,[image size].height+5);
    // Retrieve source image and begin image context
    UIImage *itemImage = image;
    CGSize itemImageSize = [itemImage size];
    CGPoint itemImagePosition;
    itemImagePosition.x = ceilf((contextRect.size.width - itemImageSize.width) / 2);
    itemImagePosition.y = ceilf((contextRect.size.height - itemImageSize.height) / 2);
    UIGraphicsBeginImageContext(contextRect.size);
    CGContextRef c = UIGraphicsGetCurrentContext();
    // Setup shadow
    CGContextSetShadowWithColor(c, shadowOffset, shadowBlur, cgShadowColor);
    // Setup transparency layer and clip to mask
    CGContextBeginTransparencyLayer(c, NULL);
    CGContextScaleCTM(c, 1.0, -1.0);
    CGContextClipToMask(c, CGRectMake(itemImagePosition.x, -itemImagePosition.y, itemImageSize.width, -itemImageSize.height), [itemImage CGImage]);
    // Fill and end the transparency layer
    CGContextSetFillColorWithColor(c, cgColor);
    contextRect.size.height = -contextRect.size.height;
    CGContextFillRect(c, contextRect);
    CGContextDrawLinearGradient(c, colorGradient,CGPointZero,CGPointMake(contextRect.size.width*1.0/4.0,contextRect.size.height),0);
    CGContextEndTransparencyLayer(c);
    //CGPointMake(contextRect.size.width*3.0/4.0, 0)
    // Set selected image and end context
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    CGColorSpaceRelease(colorSpace);
    CGGradientRelease(colorGradient);
    return resultImage;
}

- (UIImage *)imageWithShadowColor:(UIColor *)shadowColor
                     shadowOffset:(CGSize)shadowOffset
                       shadowBlur:(CGFloat)shadowBlur
{
    CGColorRef cgShadowColor = [shadowColor CGColor];
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef shadowContext = CGBitmapContextCreate(NULL, self.size.width, self.size.height,
                                                       CGImageGetBitsPerComponent(self.CGImage), 0,
                                                       colourSpace, kCGImageAlphaPremultipliedLast);
    CGColorSpaceRelease(colourSpace);
    
    // Setup shadow
    CGContextSetShadowWithColor(shadowContext, shadowOffset, shadowBlur, cgShadowColor);
    CGRect drawRect = CGRectMake(-shadowBlur, -shadowBlur, self.size.width + shadowBlur, self.size.height + shadowBlur);
    CGContextDrawImage(shadowContext, drawRect, self.CGImage);
    
    CGImageRef shadowedCGImage = CGBitmapContextCreateImage(shadowContext);
    CGContextRelease(shadowContext);
    
    UIImage * shadowedImage = [UIImage imageWithCGImage:shadowedCGImage];
    CGImageRelease(shadowedCGImage);
    
    return shadowedImage;
}

- (UIImage *)imageByApplyingAlpha:(CGFloat)alpha {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);
    
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, self.size.width, self.size.height);
    
    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);
    
    CGContextSetBlendMode(ctx, kCGBlendModeMultiply);
    
    CGContextSetAlpha(ctx, alpha);
    
    CGContextDrawImage(ctx, area, self.CGImage);
    
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return newImage;
}

- ( void ) saveToAlbumWithMetadata: ( NSDictionary * ) metadata customAlbumName: ( NSString * ) customAlbumName completionBlock: ( void ( ^ )( void )) completionBlock failureBlock: ( void ( ^ )( NSError * error )) failureBlock { NSData * imageData = UIImagePNGRepresentation ( self ); ALAssetsLibrary * assetsLibrary = [[ ALAssetsLibrary alloc ] init ]; void ( ^ AddAsset )( ALAssetsLibrary * , NSURL * ) = ^ ( ALAssetsLibrary * assetsLibrary , NSURL * assetURL ) { [ assetsLibrary assetForURL : assetURL resultBlock :^ ( ALAsset * asset ) { [ assetsLibrary enumerateGroupsWithTypes : ALAssetsGroupAll usingBlock :^ ( ALAssetsGroup * group , BOOL * stop ) { if ([[ group valueForProperty : ALAssetsGroupPropertyName ] isEqualToString : customAlbumName ]) { [ group addAsset : asset ]; if ( completionBlock ) { completionBlock (); } } } failureBlock :^ ( NSError * error ) { if ( failureBlock ) { failureBlock ( error ); } }]; } failureBlock :^ ( NSError * error ) { if ( failureBlock ) { failureBlock ( error ); } }]; }; [ assetsLibrary writeImageDataToSavedPhotosAlbum : imageData metadata : metadata completionBlock :^ ( NSURL * assetURL , NSError * error ) { if ( customAlbumName ) { [ assetsLibrary addAssetsGroupAlbumWithName : customAlbumName resultBlock :^ ( ALAssetsGroup * group ) { if ( group ) { [ assetsLibrary assetForURL : assetURL resultBlock :^ ( ALAsset * asset ) { [ group addAsset : asset ]; if ( completionBlock ) { completionBlock (); } } failureBlock :^ ( NSError * error ) { if ( failureBlock ) { failureBlock ( error ); } }]; } else { AddAsset ( assetsLibrary , assetURL ); } } failureBlock :^ ( NSError * error ) { AddAsset ( assetsLibrary , assetURL ); }]; } else { if ( completionBlock ) { completionBlock (); } } }]; }

@end;