如何在iPhone objective-c中降低图像质量/尺寸？

Question

我有一个应用程序,让用户用他/她的iPhone拍照,并将其用作应用程序的背景图像.我用UIImagePickerController它让用户拍照并将背景UIImageView图像设置为返回的UIImage对象.

IBOutlet UIImageView *backgroundView;

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo {
 backgroundView.image = image;
 [self dismissModalViewControllerAnimated:YES];
}

一切正常.如何减小UIImage480x320 的大小,以便我的应用程序可以节省内存？我不在乎我是否放弃任何图像质量.

提前致谢.

Answer 1

您可以创建图形上下文,将图像绘制为所需比例的图像,然后使用返回的图像.例如:

UIGraphicsBeginImageContext(CGSizeMake(480,320));

CGContextRef            context = UIGraphicsGetCurrentContext();

[image drawInRect: CGRectMake(0, 0, 480, 320)];

UIImage        *smallImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();    

Answer 2

我知道这个问题已经解决了,但是如果有人(像我一样)想要保持纵横比来缩放图像,这段代码可能会有所帮助:

-(UIImage *)resizeImage:(UIImage *)image toSize:(CGSize)size
{
    float width = size.width;
    float height = size.height;

    UIGraphicsBeginImageContext(size);
    CGRect rect = CGRectMake(0, 0, width, height);

    float widthRatio = image.size.width / width;
    float heightRatio = image.size.height / height; 
    float divisor = widthRatio > heightRatio ? widthRatio : heightRatio;

    width = image.size.width / divisor; 
    height = image.size.height / divisor;

    rect.size.width  = width;
    rect.size.height = height;

    if(height < width)
        rect.origin.y = height / 3;

    [image drawInRect: rect];

    UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();   

    return smallImage;
}