How to calculate the correct zoom factor?

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Hello everyone,
I have a problem.
I have an image that comes from a camera.
I stretch the image inside a Viewbox which is 877*877 px big.
The camera image can have a resolution fromm 100*100 px to 3000*3000 px.
Right now the complete image is stretched inside the ViewBox with the help of Windows.ScaleTransform.
I also have a zoom function in the software which works correctly. It also works with Windows.ScaleTransform.
It looks like this:
http://i.stack.imgur.com/tZJGI.png[^]

Now to my problem: The zoom factor has to be 100% (1) when the camera is image is 877*877, but it is always 100% when the zoom is not working.
When the Viewbox show's a stretched 3000x3000 px image the zoom should be 29% and not 100%.
Any idea how I can manage this?

I am looking forward to an answer.
Greetings
Richard

What I have tried:

I tried to calculate the resolution difference between the Image and the Viewbox
And
I tried to calculate the zoom factor

Posted 16-Jun-16 1:46am

Evosoul04

Updated 20-Jun-16 3:11am

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Richard MacCutchan 16-Jun-16 10:45am

I tried to calculate
Exactly how, and what were the problems? Please show your code and explain where it goes wrong. Also, what is the problem with Windows.ScaleTransform?

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Evosoul04 · Accepted Answer · 2016-06-20T03:11:00

Solution 1

I found the solution. It was a mistake in my thoughts. I thought that the before the Scale were done with the ScaleFactor i had to work with the Stretch. So my "formula" was easy:
Viewboxsize/Imagesize*100*ScaleFactor

Posted 20-Jun-16 3:11am

Evosoul04