# Photomicrograph and mm2 or cm2



## three_eyed_otter (Nov 4, 2008)

If you have any experience when imaging with a microscope please help...

In my professors lab I have been given the task of counting capillay density from rat heart transverse cross-sections.  Nobody in the lab knows hows to get to mm2 or cm2 after taking an image.  We use image pro plus and an olympus Ix 71 to capture the images @ 20x magnification.  Basically when reporting the # of capillaries counted current literature usually expresses it as mm2 or cm2.  So after taking my image I am uncertain of the area that I am counting from.  How can I figure out how many mm2 or cm2 my counting area is.

Thanks...

have a good one
3Eo


----------



## Garbz (Nov 5, 2008)

Well the 20x magnification is easy. An object that is 50microns in real life will appear 1mm wide on the sensor of the imaging microscope.
Once you know your sensor dimensions you can easily work backwards from there. e.g. If the sensor is 5mm wide then an object taking up 1/5th of the width at 20x magnification is 50microns wide.

Converting between mm^2 and cm^2 is just taking the square of the size between them. 10mm = 1cm therefore 10^2mm^2 = 100mm^2 = 1cm^2

Btw quick tip for the scientists out there: http://www.google.com/search?q=100mm^2+in+cm^2 Google has a VERY powerful unit converter built in.


----------



## Helen B (Nov 5, 2008)

The best way is usually to start with an image of something of a known size, such as a scale or graticule. Take a picture of it at the working magnification, then measure the known distance in pixels using the software. Rotate the image so the object is parallel with the image side, then crop or select or whatever the known dimension (without resampling). You now know the relationship between the pixels in the image and the linear dimension of the object. You can then convert from pixel dimensions to area. Some photo editing software will do this kind of thing more easily than others.

If you want, you can then set the image ppi to match the true ppi, then the image size will match the real size.

Best,
Helen


----------



## three_eyed_otter (Nov 7, 2008)

Hey guys,

Thanks for the responses and link...They've really helped.

have a good one
3Eo


----------

