Extract values from colormap

Hi everyone. I have an image where each pixel has a specific color. Each color represents a range for values, let's say: brown (value from 0 to 0.3), yellow (from 0.3 to 0.6) and green (from 0.6 to 0.9). The idea is to extract the corresponding value depending on the color for each pixel. Therefore, what I did was: Load the image using imread or readgeoraster, create a colormap. What I should do next is to define a range of values for every color and then extract the corresponding values.

% Load the image
[RasterName,RasterPath]=uigetfile('.tif','Select file');
[A,R]=readgeoraster([RasterPath,RasterName]);
p=R.ProjectedCRS;
[x,y]=worldGrid(R);
[lat,lon]=projinv(p,x,y);
InfoRaster=geotiffinfo([RasterPath,RasterName]);
RR=InfoRaster.GeoTIFFTags.GeoKeyDirectoryTag;

% Create a colormap
c1=[183,119,5]/255;
c2=[242,242,0]/255;
c3=[214,225,0]/255;
c4=[193,211,0]/255;
c5=[172,196,0]/255;
c6=[150,181,0]/255;
c7=[129,167,0]/255;
c8=[108,152,0]/255;
c9=[87,138,0]/255;
c10=[66,123,0]/255;
c11=[44,108,0]/255;
c12=[23,94,0]/255;
cmap=createcolormap(c1,c2,c3,c4,c5,c6,c7,c8,c9,c10,c11,c12);

% Define range of values for every color
color_range_1=[183,119,5,255,0.00,0.10];
color_range_2=[242,242,0,255,0.11,0.20];
color_range_3=[214,225,0,255,0.21,0.30];
color_range_4=[193,211,0,255,0.31,0.40];
color_range_5=[172,196,0,255,0.41,0.50];
color_range_6=[150,181,0,255,0.51,0.60];
color_range_7=[129,167,0,255,0.61,0.70];
color_range_8=[108,152,0,255,0.71,0.80];
color_range_9=[87,138,0,255,0.81,0.90];
color_range_10=[66,123,0,255,0.91,1.00];
color_range_11=[44,108,0,255,1.01,1.10];
color_range_12=[23,94,0,255,1.11,1.20];

Answer 1

[Walter Roberson]

Put your color_range information together into one 12 x 6 array. Extract the first 3 columns, divide by 255 to get colors in the range 0 to 1. Use those as the colormap parameter with the image and rgb2ind(). The result should be an array of indices into the color_range array, which you can then use to pull out the range columns.

[eddie]

Hi, many thanks for your response. I have now the following code:

clear all, close all, clc;

%% Part - I

[RasterName,RasterPath]=uigetfile('.tif','Select file');
[A,R]=readgeoraster([RasterPath,RasterName]);
p=R.ProjectedCRS;
[x,y]=worldGrid(R);
[lat,lon]=projinv(p,x,y);
InfoRaster=geotiffinfo([RasterPath,RasterName]);
RR=InfoRaster.GeoTIFFTags.GeoKeyDirectoryTag;

%% Part - II

[SetName,SetPath]=uigetfile('.xlsx','Select file');
Data=importdata([SetPath,SetName]);
Data=Data.data(:,3:end);
cmap=createcolormap(Data(:,1:3));
X=rgb2ind(A(:,:,1:3),cmap);

Where Data is the 12 x 6 array. The result I get is a matrix ranging from 1 to 255, but I couldn't set the values depending on each color. What should I do?

[Walter Roberson]

range_min = Data(X, 5);
range_max = Data(X, 6);

[eddie]

Many thanks for your help!