Calculating minimumZoomScale of a UIScrollView

I have an image that I want to load into an image view and set the minimumZoomScale, as well as the zoomScale to an aspectFill like scale that I calculate as follows:

// configure the map image scroll view
iImageSize = CGSizeMake(iImageView.bounds.size.width, iImageView.bounds.size.height);
iScrollView.minimumZoomScale = iScrollView.bounds.size.height / iImageSize.height;
iScrollView.maximumZoomScale = 2;
iScrollView.zoomScale = iScrollView.minimumZoomScale;
iScrollView.contentOffset = CGPointMake(0, 0);
iScrollView.clipsToBounds = YES;

The iScrollView size is 450 x 320px and the iImageSize is 1600 x 1960px.

Doing the minimumZoomScale math by hand: 450 / 1960 = 0.22959184开发者_JS百科. The system determines 0.234693885 instead (???).

But to get the window fit into the 450px space, both figures don't work (!!!). I manually tried and found 0.207 is the right number (that would translate to a image height of 2174 xp or alternatively a UIScrollView height of 406px).

For information: the UIScrollview screen is 450px, namely 480px minus status bar height (10), minus UITabBar height (20)

Any clues on this misbehaviour?

Not sure if you still have this problem, but for me, the scale is exactly the opposite. minimumZoomScale = 1 for me and I have to calculate the maximumZoomScale.

Here's the code:

[self.imageView setImage:image];
// Makes the content size the same size as the imageView size.
// Since the image size and the scroll view size should be the same, the scroll view shouldn't scroll, only bounce.
self.scrollView.contentSize = self.imageView.frame.size;

// despite what tutorials say, the scale actually goes from one (image sized to fit screen) to max (image at actual resolution)
CGRect scrollViewFrame = self.scrollView.frame;
CGFloat minScale = 1;
// max is calculated by finding the max ratio factor of the image size to the scroll view size (which will change based on the device)
CGFloat scaleWidth = image.size.width / scrollViewFrame.size.width;
CGFloat scaleHeight = image.size.height / scrollViewFrame.size.height;
self.scrollView.maximumZoomScale = MAX(scaleWidth, scaleHeight);
self.scrollView.minimumZoomScale = minScale;
// ensure we are zoomed out fully
self.scrollView.zoomScale = minScale;

For simple zoom in/out i generally use below code. minimumZoomScale= 1 sets initial zoom to current image size. I have given maximumZoomScale = 10 which can be calculated from actual ratio of image size and container frame size.

[scrollView addSubview: iImageView];
    scrollView.contentSize = iImageView.frame.size;
    scrollView.minimumZoomScale = 1.0;
    scrollView.maximumZoomScale = 10;
    [iImageView setFrame:CGRectMake(0, 0, 450, 320)];
[scrollView scrollRectToVisible:iImageView.frame animated:YES];