Hi,
To make it easier. I have two pictures of a balloon.
1st picture: the balloon is inflated, has shape but not inflated fully.
2nd picture: the balloon is inflated full.
The distance between the balloon and the camera is static.
Is there a way to know the relative change in size dimension of the balloon. Remember, this is a non-linear shape, so its not a circle, oval balloon. Can I measure the changes in the expansion?
The only way I know now is unscientifically make a grid plot on the image and count the grids from there.
Thanks for the help
How to measure the difference in a 2D non-linear shape which changes in size?
Yeah, there are ways but they're a bit complicated to describe here (computer vision, principal axis analysis).
However computing the area changes should be pretty easy; just count the number of non-background pixels in the image and that will give you the area of the balloon. =P
How to measure the difference in a 2D non-linear shape which changes in size?
You can determine the change in surface area or volume using formulas for spheres (work either with radii or diameters). If the balloon is oval solve for a short diameter then a long diameter and average the results for a fair approximation. The skin expands more where it has thinned more. If you don't know the actual diameter of the balloon (small or large) assign unity (1) to small and determine the relative increase.
If the balloon is highly non-spherical, perhaps divide it into two spheres in one volume. Likely the true shape may change with the degree of inflation permitting only an approximation from a photo. Actual balloons in hand could be used to displace water from a topped off container to determine volumes of the balloons.
