# Multilevel image thresholding combining distinct colors

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Kasthuri Kannan on 30 Oct 2019
Commented: KALYAN ACHARJYA on 8 Nov 2019
I am trying to segment an image. It has 8 distinct colors (regions) excluding the background white. I am using multilevel thresholding with 8 levels out of which 6 regions are segmented properly. However, the method combines two regions which is highlighted in circles. Clearly, the grayscale image (middle) also shows the difference for this region. I am not sure how to get this regions segmented along with the rest of the regions. Any help will be much appreciated. I am also reproducing the code below.
% Read the image and convert into grayscale
I = rgb2gray(I);
% Define thresholds for the 8 distinct regions excluding the white background
thresh = multithresh(I,8)
% Segment the image and display
seg_I = imquantize(I,thresh);
imshow(seg_I == 6)
KALYAN ACHARJYA on 31 Oct 2019
Edited: KALYAN ACHARJYA on 2 Nov 2019
There are distinct difference between those two labels in the circles (2nd Image).
Kasthuri Kannan on 31 Oct 2019
Yes, there is - actually I managed to find out the actual gray level for those regions and used the values to segment them, instead of the method to automatically determine them.

Kritika Bansal on 6 Nov 2019
Hi,
I tried replicating the issue on my end, but the output comes out to be correct in my case when I ran the following commands on MATLAB Online R2019b.
These are the commands I used:
clear all; clc;
imshow(I);
I = rgb2gray(I);
% Define thresholds for the 8 distinct regions excluding the white background
[thresh, metric] = multithresh(I,8)
% Segment the image and display
seg_I = imquantize(I,thresh);
figure, imshow(seg_I, []);
figure, imshow(label2rgb(seg_I));
Following is the output:
thresh =
1×8 uint8 row vector
23 61 90 116 146 168 182 219
metric =
0.9982
I am also attaching the input and output images for your reference.
Kasthuri Kannan on 8 Nov 2019
Thanks. I think the R2019b solves this -
KALYAN ACHARJYA on 8 Nov 2019
+1
Truly

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