objective-c - UIimage可以改变图片的大小和分辨率吗？

Question

如果我选择一张640*960图片并将其放入200*300UIImage 中，那么该图片将作为图片上传到服务中200*300。

Answer 1

您可以使用以下方法调整图像大小：

+ (UIImage *) imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
    //UIGraphicsBeginImageContext(newSize);
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}
+ (UIImage *) imageWithImage: (UIImage*) sourceImage scaledToWidth: (float) i_width {//method to scale image accordcing to width

    float oldWidth = sourceImage.size.width;
    float scaleFactor = i_width / oldWidth;

    float newHeight = sourceImage.size.height * scaleFactor;
    float newWidth = oldWidth * scaleFactor;

    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight));
    [sourceImage drawInRect:CGRectMake(0, 0, newWidth, newHeight)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 2

- (void)viewDidLoad
{
      [super viewDidLoad];
       // Create the image from a png file
       imageOriginal = [UIImage imageNamed:@"bg-640by960.png"];
       imageView =[[UIImageView alloc] initWithImage:imageOriginal];
       imageView.tag=200;

      // Get size of current image
      size = [imageOriginal size];
// Frame location in view to show original image
[imageView setFrame:CGRectMake(0, 0, size.width, size.height)];
[[self view] addSubview:imageView];
[self.view bringSubviewToFront:btnCrop];

//To resize image call below method
[[self.view viewWithTag:200] removeFromSuperview];
[self squareImageWithImage:imageOriginal scaledToSize:CGSizeMake(200, 300)];
}

- (UIImage *)squareImageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize
{
 double ratio;
double delta;
CGPoint offset;

//make a new square size, that is the resized imaged width
CGSize sz = CGSizeMake(newSize.width, newSize.width);

//figure out if the picture is landscape or portrait, then
//calculate scale factor and offset
if (image.size.width > image.size.height) {
    ratio = newSize.width / image.size.width;
    delta = (ratio*image.size.width - ratio*image.size.height);
    offset = CGPointMake(delta/2, 0);
} else {
    ratio = newSize.width / image.size.height;
    delta = (ratio*image.size.height - ratio*image.size.width);
    offset = CGPointMake(0, delta/2);
}

//make the final clipping rect based on the calculated values
CGRect clipRect = CGRectMake(-offset.x, -offset.y,
                             (ratio * image.size.width) + delta,
                             (ratio * image.size.height) + delta);


//start a new context, with scale factor 0.0 so retina displays get
//high quality image
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
    UIGraphicsBeginImageContextWithOptions(sz, YES, 0.0);
} else {
    UIGraphicsBeginImageContext(sz);
}
UIRectClip(clipRect);
[image drawInRect:clipRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
imageView =
[[UIImageView alloc] initWithImage:newImage];
[imageView setFrame:CGRectMake(60, 60, newSize.width, newSize.height)];
[self.view addSubview:imageView];
return newImage;
}