how can i compare between the levels or brightness from 2 pictures?

KV
Posted By
Kobi_Vardi
May 17, 2008
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511
Replies
2
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Closed
Hi try to compare between the levels of two surfaces that i photographed. i want to export the levels graph or to get numerical values of the pixels so that i would be able to make and to compare between graphs. i tried to save thw levels graphs and couldnt do it. does anyone have an idea how it can be done?

another question is, lets say that i want to measure an area of a selected colodr in a picture. how do i do that? i am interested in measuring the sixe of certain features (colors) on the surfaces that i photographed. can photoshop do that? can i export the picture data into another software to do it? and if so which software…i’ve been trying to find one on the web an i didnt succeed.
thanks
Kobi
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C
Curvemeister
May 17, 2008
Check out the free listpx utility:
http://www.nist.gov/lispix/

The scatter plot functionality sounds like it might be what you want for creating comparison plots of corresponding points in two images: http://www.nist.gov/lispix/doc/TOOLS/scat-plot-new.htm

For example, you could take two shots of a surface under differing conditions, and create a 3D scatter plot that compares the two images visually.

Another common way to deal with numeric color values is to save selected areas of the image in Photoshop as raw files (these are unformatted pixel values, which are different from camera raw files), and then read them into Matlab and/or Excel for processing.

The curvemeister plugin might be useful – email me offline if you would like to know more. Mike at curvemeister dot com
GA
George_Austin
May 18, 2008
Kobi

Use the expanded histogram to get the pixel count in any selected area and divide by the pixel count for the entire image. Multiply the total image area by this ratio to get the selected area.

You can compare the mean luminosities of two images also using the expanded histogram.

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