help on computing scale

[codesearcher]

I have this actual picture with size width and height at 14x17 inches. In px @ 96 dpi, that is 1344x1632 then multiplied it by 35% and that is 470.4px x 571.2px for my fixed size of my image element.

Now I have this new picture with size 8 x 10 inches In px @ 96 dpi, that is 768x960. But I have a fixed sized of 470.4px x 571.2px for width and height.

Now I want to know what is the percentage of zoom factor where I can say that when I multiply 768 and 960, the result will be 470.40 and 571.20.

Maybe you will advice me, to divide 470.40 by 768 and 571.20 by 960, then add the result and divide that by 2 to get the average zoom factor. But I am not sure if that is the right computation.

[passel]

If you want to zoom the picture proportionally and not clip any of the picture, then you wouldn't average, you would use the smaller ratio as the zoom.
In your example 470.4/768=.6125 and 571.2/960=.595 so your zoom value would be .595 to fill the 960 direction fully filling the 571.2 dimension and the 470.4 dimension wouldn't be filled, there would be 13.44 pixels unused, so you could center the image in that direction by offsetting by 7 pixels.

If you used the average value, then you would loose some portion of the image in one direction (14 pixels of your original image) and still have a gap, (1/2 the size of the original gap, so around 7 pixels), in the other direction.