Color thresholding and obtaining Lab values

Posted by Rie Sadohara on May 22, 2018; 9:13pm
URL: http://imagej.273.s1.nabble.com/Color-thresholding-and-obtaining-Lab-values-tp5020700.html

Hello all,

I am trying to get Lab values from images of yellow beans. There are some black and white parts in the image, so I want to remove those parts and measure the yellowness of the bean seeds. Below are the steps I took, but Lab values are calculated from the entire image. Could someone tell me how to do it right?

1. Open --> Open my photo, which is an RGB color image.
2. Image --> Adjust --> Color threshold... --> Then set the threshold of L* value to be 71-216 so that the black and white parts will be excluded. --> Select.
3. The yellow parts (of which I want to know the Lab values) are circled with yellow lines now.
4.  Image --> Type --> Lab stack.
5. Analyze --> Measure. for each stack (L, a, and b)
6. The returned Lab values are based on the entire image. It works as though there had been no color thresholding.

My understanding is that the parts that are circled with bright yellow lines after color thresholding are the area that are going to be used for Lab measurements? (Please see the attachment. In the image, the yellow parts (my ROI) are segregated correctly, but how can I get Lab values out of this region?)

Any advice would be greatly appreciated,

Rie


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