How to convert area of blobs in pixels to meters?

I want to convert the area of blobs which is in pixels to meters. How to do this?

Thanks in advance.

Answer 1

[Walter Roberson]

Multiply the area by the height each pixel represents in meters, and by the width each pixel represents in meters, to get a result.

If the image is non-linear so that the heights and widths represented by the pixels are not constant, then you need to linearize first.

The difficult part of the task can be figuring out what heights and widths are represented by the pixels. Unless you have good quality information about the aperature and distance (or equivalent information) then you will typically need an object of known size in the field of view. If you are taking pictures of scenes you will typically need either at least two cameras (stereo) or else a second information channel that is measuring depth (such as laser, ultrasonic)

Note: if you have EXIF information that contains resolution information.. ignore it. Unless, that is, you are working with an instrument created specifically as a science device, in which case possibly it might be meaningful... but usually it is not.

[swati mane]

Thank you sir for your answer.

I didnt understood : "Multiply the area by the height each pixel represents in meters, and by the width each pixel represents in meters, to get a result" How to do this?

Actually I am having image of the road traffic, for which i have calculated the total area of blobs (area covered by the vehicles) and I want to convert this area in meters.

Thanks in advance.

[Walter Roberson]

You need stereo registration for that. Because of perspective, not all positions in the picture represent equal distances, so covering a certain area in one part of the image represents a different area than if the same number of pixels are covered in a different part of the image.

[swati mane]

ok Sir. Thank you.