Digital zoom calculations
Posted: 14 May 2009, 01:13
If I have a 5MP 1/2" camera with a 20mm lens looking at an object 220m away and I want person ID, how do I calculate this.
Based on and email from Stanislav Utochkin, to get a 2X digital zoom, which to me is a 40mm effective lens, I make the camera 1.2MP.
As this is 1/4 I did some homework :
Based on and email from Stanislav Utochkin, to get a 2X digital zoom, which to me is a 40mm effective lens, I make the camera 1.2MP.
As this is 1/4 I did some homework :
Apparently the distant object will also show any camera shake more dramatically.http://www.dcresource.com/forums/archiv ... -2275.html
A high megapixel is not an effective zoom replacement, but here's the maths to show why.
Let's say you have a 5 megapixel camera.
If you wanted to zoom the image in by 2x, then you would be dividing the number of effective pixels by 4, hence you'd end up with a 1.25 megapixel camera. If you wanted to zoom in by 3x, then you would be dividing the number of effective pixels by 9, hence you'd end up with a 0.56 megapixel image.
So you see, even if you want a 3x zoom, you're dividing the pixel count by nine.
I mean, a high number of pixels is good for reasonable cropping, but not for any serious zooming where you go right into a certain part of the image.