Filtering an Image and Calculating the area

[sadak]

Hi everyone,

I am currently trying to calculate the area of several white spots in my picture (almost black background). The problem is that their shape is so irregular and sometimes, they don't appear exactly white, but rather light grey or darker. So it's very hard for me to use a magic wand to select the area one by one.

Now with a black and white picture in my computer, is it possible that I filter out black or the dark grey spot from the image so that I am left with the white spot/ or light grey (the transition color) and hence I will be able to calculate the area of the white spot (including those with veyr light grey). So the idea is to filter out the image from some very black colors (or maybe intensity-wise because the image is BW).

Or maybe you have a better idea on how to directly measure those area filled with color starting from certain intensity?

I've attached the sample image.

Thank you in advance for your replies!

 

[$1r_M4x1mu$]

Hi sadak

Welcome to PhotoShop Gurus.

First things first, what you need to do in order to extract only your white spots or light gray from the image as you mentioned, is to increase the shadows and highlights on your image, via levels "Layer>Adjustment layer> Levels", meaning you need to make the dark even darker and same thing whit whites, use the levels slider to achieve such task,

Then what you need to select or isolate those color shades via "Selec>Color range" , that way you will be able to select any color shade you need to, Once on the select by color range window, you need to sample the color shades you need to extract, using the "eye dropper" tool select your color, if you need to add another shade to your selection hold the "Alt" key, while selecting colors or drag your mouse across those color shades, if you need to subtract colors from your selection hold the "Crtl" while selecting, and hit enter.

Then, on your layers palette you can just duplicate your layer whit the active selection, creating a new layer whit those selected colors or invert your selection and press the delete key, to get rid of your selection and leaving only your original selection

And for the measurements, once you got your clean layer whit out the dark or grey shades, you can select your layer "Crtl+a" and go to "Analisys> record measurements" and easily you will determine the area, perimeter, circularity, high, width, etc. Remember that the analisys tool in this case, will only work whit active selections.

See Image below



1. Analisys results, measurements window.
2. Extracted only white and light grey colors.
3. Levels Adjustment Layer.
4. Some random color background to accentuate extracted shades.

Hope this helps.

 

[sadak]

Thank you $1r_M4x1mu$ ! I will try your suggestion!

 

[sadak]

Ya, it works for me, thanks!

 

[Davin Salo]

Out of curiosity, what do you do with this information?

 

[sadak]

Hi Davin, nothing much. Just wanted to know the filling ratio. hahaha.....and rest assured, this is not for making nuclear bomb, lol.

 

[Davin Salo]

Aw, I was hoping there was some awesome application for it that I was previously unaware of. There's gotta be a reason to know doesn't there? .

 

[sadak]

In the future, maybe yes... but not now..hahaha...