How to remove objects in diferent pics if they have diferent pdi

So question is if i fave recantgle and i want to remove objects who area is lower than 0,45 cm2 and biger 5,5 cm2. I know that i can do with UL and UB but it doesnt work if have diferent pics with diferent pdi

[Image Analyst]

What is a "pdi"?

Answer 1

[Walter Roberson]

Presuming that pdi is ppi, pixels per inch, then 1/ppi is inches per pixel, and 2.54/ppi is cm per pixel. From there, (2.54/ppi)^2 is cm^2 per pixel^2, which is 6.4516/ppi^2 with units cm^2 per pixel^2.

Then, 0.45 cm^2 / (6.4516 cm^2 / ppi^2) = 0.069750139500279 * ppi^2 gives the number of square pixels for 0.45 cm^2. For example for 75 ppi then it would be about 392.3 square pixels, which is between 19x19 and 20x20