I have a thresholded image and i need to find the real area of the black region

Question

i have a thresholded image and i need to find the real area of the black region.iam new to lab view.please guide me.i have attached the image..
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Answer 1

Hello,
You have calculated the number of black pixels using a histogram, right? This is the simple part.
this is how i would approach the problem:
OPTION 1: calculate the linear magnification of your system, using the equation M = f/(f-d) = hi/ho. f is the focal lenght [mm] and d is the distance of the object from the lense [mm]. You can calculate the magnification by placing an object of known height (ho) at the distance d, and calculate the illuminated pixels (hi). Then multiply the pixels with the physical pixel size in mm. When magnification is know, you can always calculate the object size, based on the number of illuminated pixels. But this is only for the specified distance d. If the distance changes, the magnification changes also. If your area covers let's say 50 pixels, arrange it in 50 columns and 1 row. Calculate the object size using first 50 pixels and second using 1 pixel (if the pixel size in different in both directions, take this into account when calculating). Then multiply the calculated object sizes to get the area.
OPTION 2: calibrate the camera system in order to obtain the fx and fy [pix]. Calibration is really simple - use the NI Calibration training interface. Calculate the actual focal lenght in both directions:
fY[mm] = sensor_height[mm] * fy[pix]/sensor_height[pix]
fX[mm] = sensor_width[mm] * fx[pix]/sensor_width[pix]
Let's say that the area of the pixels on your image is Ap. Let's also say that we "arrange" it in Ap columns and 1 row. Calculate the actual object size in X direction:
OX[mm] = Ap * Pw[mm] * d[mm]/fX[mm]
and in the Y direction:
OY[mm] = 1 * Ph[mm] * d[mm]/fY[mm]
where Pw is the element sensor element size in horizontal and Ph in vertical direction [pix].
Then calculate the real-world area by OX*OY [mm^2].
You also need the distance d here - the previous post describes how to calculate this.
Also, hopefully, someone with more experience could comment on what i wrote above. Maybe there is a simpler solution? I am also learning stuff as i go, so any comment would be appreciated.
Hope this helps you get started.
Best regards,
K
https://decibel.ni.com/content/blogs/kl3m3n
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