UIImage图片缩放功能

直接上代码

// 缩略图功能
- (UIImage*)thumbnailOfImage:(UIImage*)image withSize:(CGSize)aSize

{
    //NSLog(@"create thumbnail image");

    if (!image)
        return nil;

    CGImageRef imageRef = [image CGImage];
    UIImage *thumb = nil;

    float _width = CGImageGetWidth(imageRef);
    float _height = CGImageGetHeight(imageRef);

    // hardcode width and height for now, shouldn't stay like that
    float _resizeToWidth;
    float _resizeToHeight;

    _resizeToWidth = aSize.width;
    _resizeToHeight = aSize.height;

    float _moveX = 0.0f;
    float _moveY = 0.0f;

    // determine the start position in the window if it doesn't fit the sizes 100%
    
    //NSLog(@" width: %f  to: %f", _width, _resizeToWidth);
    //NSLog(@" height: %f  to: %f", _height, _resizeToHeight);
    
    // resize the image if it is bigger than the screen only
    if ( (_width > _resizeToWidth) || (_height > _resizeToHeight) )
    {
        float _amount = 0.0f;

        if (_width > _resizeToWidth)
        {
            _amount = _resizeToWidth / _width;
            _width *= _amount;
            _height *= _amount;
            
            //NSLog(@"1 width: %f height: %f", _width, _height);
        }
        
        if (_height > _resizeToHeight)
        {
            _amount = _resizeToHeight / _height;
            _width *= _amount;
            _height *= _amount;
            
            //NSLog(@"2 width: %f height: %f", _width, _height);
        }    
    }

    _width = (NSInteger)_width;
    _height = (NSInteger)_height;

    _resizeToWidth = _width;
    _resizeToHeight = _height;
    
    
    CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                _resizeToWidth,
                                                _resizeToHeight,
                                                CGImageGetBitsPerComponent(imageRef),
                                                CGImageGetBitsPerPixel(imageRef)*_resizeToWidth,
                                                CGImageGetColorSpace(imageRef),
                                                CGImageGetBitmapInfo(imageRef)
                                                );

    // now center the image
    _moveX = (_resizeToWidth - _width) / 2;
    _moveY = (_resizeToHeight - _height) / 2;
    
    CGContextSetRGBFillColor(bitmap, 1.f, 1.f, 1.f, 1.0f);
    CGContextFillRect( bitmap, CGRectMake(0, 0, _resizeToWidth, _resizeToHeight));
    CGContextDrawImage( bitmap, CGRectMake(_moveX, _moveY, _width, _height), imageRef );
    
    // create a templete imageref.
    CGImageRef ref = CGBitmapContextCreateImage( bitmap );
    thumb = [UIImage imageWithCGImage:ref];

    // release the templete imageref.
    CGContextRelease( bitmap );
    CGImageRelease( ref );

    return [[thumb retain] autorelease];
    
}

// 等比例缩放
- (UIImage *)scaleImage:(UIImage *)image toScale:(float)scaleSize

{
    UIGraphicsBeginImageContext(CGSizeMake(image.size.width * scaleSize, image.size.height * scaleSize));
    [image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height * scaleSize)];
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return scaledImage;
    
}