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sjamis
sjamis
Participant
July 27, 2017
Question

newbie needing help calculating precent area

  • July 27, 2017
  • 3 replies
  • 430 views

Hey all,

new to Photoshop and trying to use it for academic research. I have some images of soils that we collected, and I don't want to disturb the soils in their cores. The soils have a good amount of chunks of charcoal littered throughout. I want to use the images I took to determine what % of the total area of the image is made up of charcoal chunks. Is there any way to do that on Photoshop?

SJ

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    3 replies

    Chuck Uebele
    Community Expert
    Chuck UebeleCommunity Expert
    Community Expert
    July 28, 2017

    If the charcoal is just the dark spots, you would want to isolate the sample from the rest of the image. Then use color range to target the dark areas of the sample to make a selection. Once you have a selection, you can use analysis to get the area of the selections. You can then figure out a percentage from that:

    Norman Sanders
    Norman Sanders
    Legend
    July 27, 2017

    SJ, obtaining your desired result is a two step process:

    1. Isolating the carbon in the image

    2. Determining the percent of the area it occupies.

    Step 2 is easy part: The expanded view of the Histogram panel will provide the pixel count of the total image and of the isolated area. A simple proportion will provide the percent.

    Step 1 depends upon the difference in tone value between the carbon and the non-carbon area and for that, we would like to see the  a sample image. That amount of difference will determine whether Photoshop can isolate the tone and the method to be used to accomplish it. To repeat: post a sample image so that we can make an assessment of the job to be done and provide instructions to you.

    sjamis
    sjamisAuthor
    Participant
    July 27, 2017

    the really dark bits are charcoal

    Norman Sanders
    Norman Sanders
    Legend
    July 27, 2017

    The photograph poses several problems and for you to have any chance of success, it must be reshot. The image is unevenly lit, has a glaring hot spot without any information, has inadequate depth of field and lacks sharp focus. It requires shadowless lighting, a yellow/orange filter (Perhaps a Wratten No. 15) to enhance contrast and adequate depth of field that encompasses the entire core depth, plus a white background and absolutely crisp focus. With sufficient file size and resolution plus added contrast via Photoshop we may be able to isolate the fine grains appearing in the core. This image is not suited for the job. Sorry.

    Nancy OShea
    Community Expert
    Nancy OSheaCommunity Expert
    Community Expert
    July 27, 2017

    The would depend on the size and quality of images you have to work with. 

    The Histogram panel might be useful.

    View histograms and pixel values in Photoshop

    Nancy

    Nancy O'Shea— Product User & Community Expert
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