iPhone图片ＵIImage对象操作的一些方法 ［转］

http://mobile.51cto.com/iphone-284346.htm

iPhone开发应用UIImage图片对象操作是本文要介绍的内容，主要来学习UIImage图片对象操作，内容不多，主要是以代码实现图片对象的操作。

1、根据给定得图片，从其指定区域截取一张新得图片。

-(UIImage *)getImageFromImage{
    //大图bigImage
    //定义myImageRect，截图的区域
    CGRect myImageRect = CGRectMake(10.0, 10.0, 57.0, 57.0);
    UIImage* bigImage= [UIImage imageNamed:@"k00030.jpg"];
    CGImageRef imageRef = bigImage.CGImage;
    CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef, myImageRect);
    CGSize size;
    size.width = 57.0;
    size.height = 57.0;
    UIGraphicsBeginImageContext(size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, myImageRect, subImageRef);
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();
    return smallImage;
}

2、针对UIImage得一些常用缩放得方法：

-(UIImage*)resizedImage1:(UIImage*)inImage  inRect:(CGRect)thumbRect {
    // Creates a bitmap-based graphics context and makes it the current context.
    UIGraphicsBeginImageContext(thumbRect.size);
    [inImage drawInRect:thumbRect];
    return UIGraphicsGetImageFromCurrentImageContext();
}
-(UIImage*)resizedImage2:(UIImage*)inImage  inRect:(CGRect)thumbRect {
    CGImageRef          imageRef = [inImage CGImage];
    CGImageAlphaInfo    alphaInfo = CGImageGetAlphaInfo(imageRef);
    /* There's a wierdness with kCGImageAlphaNone and CGBitmapContextCreate
    see Supported Pixel Formats in the Quartz 2D Programming Guide
    Creating a Bitmap Graphics Context section
    only RGB 8 bit images with alpha of kCGImageAlphaNoneSkipFirst,
          kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst,and kCGImageAlphaPremultipliedLast,
          with a few other oddball image kinds are supported
The images on input here are likely to be png or jpeg files*/
    if (alphaInfo == kCGImageAlphaNone)
        alphaInfo = kCGImageAlphaNoneSkipLast;
        // Build a bitmap context that's the size of the thumbRect
       CGFloat bytesPerRow;
    if( thumbRect.size.width > thumbRect.size.height ) {
       bytesPerRow = 4 * thumbRect.size.width;
    } else {
       bytesPerRow = 4 * thumbRect.size.height;
    }
    CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                        thumbRect.size.width,       // width
                                                        thumbRect.size.height,      // height
                                                        8, //CGImageGetBitsPerComponent(imageRef),  // really needs to always be 8
                                                        bytesPerRow, //4 * thumbRect.size.width,    // rowbytes
                                                        CGImageGetColorSpace(imageRef),
                                                        alphaInfo
);
    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, thumbRect, imageRef);
    // Get an image from the context and a UIImage
    CGImageRef  ref = CGBitmapContextCreateImage(bitmap);
    UIImage*    result = [UIImage imageWithCGImage:ref];
    CGContextRelease(bitmap);   // ok if NULL
    CGImageRelease(ref);
    return result;
}
- (UIImage *)scaleImage:(UIImage *) image maxWidth:(float) maxWidth maxHeight:(float) maxHeight
{
    CGImageRef imgRef = image.CGImage;
    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);
    if (width <= maxWidth && height <= maxHeight)
    {
        return image;
    }
    CGAffineTransform transform = CGAffineTransformIdentity;
    CGRect bounds = CGRectMake(0, 0, width, height);
    if (width > maxWidth || height > maxHeight)
    {
        CGFloat ratio = width/height;
        if (ratio > 1)
        {
            bounds.size.width = maxWidth;
            boundsbounds.size.height = bounds.size.width / ratio;
        }
        else
        {
            bounds.size.height = maxHeight;
             boundsbounds.size.width = bounds.size.height * ratio;
        }
    }
    CGFloat scaleRatio = bounds.size.width / width;
    UIGraphicsBeginImageContext(bounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextScaleCTM(context, scaleRatio, -scaleRatio);
    CGContextTranslateCTM(context, 0, -height);
    CGContextConcatCTM(context, transform);
    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return imageCopy;
}

3、其他缩放UIImage的size，有需要的可以看看

-(UIImage*) scaleAndRotateImage:(UIImage*)photoimage:(CGFloat)bounds_width:(CGFloat)bounds_height
{
    //int kMaxResolution = 300;
    CGImageRef imgRef =photoimage.CGImage;
    CGFloat width = CGImageGetWidth(imgRef);
    CGFloat height = CGImageGetHeight(imgRef);
    CGAffineTransform transform = CGAffineTransformIdentity;
    CGRect bounds = CGRectMake(0, 0, width, height);
    /*if (width > kMaxResolution || height > kMaxResolution)
    {
        CGFloat ratio = width/height;
        if (ratio > 1)
        {
            bounds.size.width = kMaxResolution;
            boundsbounds.size.height = bounds.size.width / ratio;
        }
        else
        {
            bounds.size.height = kMaxResolution;
            boundsbounds.size.width = bounds.size.height * ratio;
        }
    }*/
    bounds.size.width = bounds_width;
    bounds.size.height = bounds_height;
    CGFloat scaleRatio = bounds.size.width / width;
    CGFloat scaleRatioheight = bounds.size.height / height;
    CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
    CGFloat boundHeight;
    UIImageOrientation orient =photoimage.imageOrientation;
    switch(orient)
    {
        case UIImageOrientationUp: //EXIF = 1
            transform = CGAffineTransformIdentity;
            break;
        case UIImageOrientationUpMirrored: //EXIF = 2
            transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            break;
        case UIImageOrientationDown: //EXIF = 3
            transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;
        case UIImageOrientationDownMirrored: //EXIF = 4
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
            transform = CGAffineTransformScale(transform, 1.0, -1.0);
            break;
        case UIImageOrientationLeftMirrored: //EXIF = 5
            boundHeight = bounds.size.height;
            boundsbounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
            transform = CGAffineTransformScale(transform, -1.0, 1.0);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;
        case UIImageOrientationLeft: //EXIF = 6
            boundHeight = bounds.size.height;
            boundsbounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
            transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
            break;
        case UIImageOrientationRightMirrored: //EXIF = 7
            boundHeight = bounds.size.height;
            boundsbounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeScale(-1.0, 1.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;
        case UIImageOrientationRight: //EXIF = 8
            boundHeight = bounds.size.height;
            boundsbounds.size.height = bounds.size.width;
            bounds.size.width = boundHeight;
            transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
            transform = CGAffineTransformRotate(transform, M_PI / 2.0);
            break;
        default:
            [NSException raise:NSInternalInconsistencyException format:@"Invalid?image?orientation"];
            break;
    }
    UIGraphicsBeginImageContext(bounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft)
    {
        CGContextScaleCTM(context, -scaleRatio, scaleRatioheight);
        CGContextTranslateCTM(context, -height, 0);
    }
    else
    {
        CGContextScaleCTM(context, scaleRatio, -scaleRatioheight);
        CGContextTranslateCTM(context, 0, -height);
    }
    CGContextConcatCTM(context, transform);
    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
    UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return imageCopy;
}