How to extract raw data from a rgb image visualized with known colormap?

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Xin Liu
Xin Liu 2022 年 10 月 24 日
編集済み: Xin Liu 2022 年 10 月 27 日
Hello, everyone,
I have a rgb image, and it was visualized with a known colormap. Now I want to extract the raw 2D matrix data rather than RGB values of this image before it was mapped to the colormap . How should I do?
Here is an example:
raw_data = rand(256,256);
axis image off;
title('saved image');
Then I save this visualized image, names as, for example 'saved image.jpg'.
How should I retrieve 'raw_data' from 'saved_img.jpg' according to the known 'jet' colormap?
Thank you!

回答 (1 件)

Sameer Pujari
Sameer Pujari 2022 年 10 月 27 日
Hello Xin Liu
From the given info, I understand that you want to get RGB image back after you have visualised with a known colormap.
To do that you have to first get the colormap of orignal rgb image
RGB = imread('image.jpg');
[X,cmap] = rgb2ind(RGB,65536);
Then you can get the original image back using
X = ind2rgb(X,cmap);
The same can be done by using "colormap" function for the figure
RGB = imread('image.jpg');
[X,map] = rgb2ind(RGB,65536);
axis off
axis image
colormap(parula) %image will be visualized in parula colormap
colormap(cmap) %image will be visualized in orignal rgb colormap
I hope this information helps you!
  3 件のコメント
Xin Liu
Xin Liu 2022 年 10 月 27 日
編集済み: Xin Liu 2022 年 10 月 27 日
Hi Sameer,
Thank you for your code. You may misunderstand my purpose. My purpose is to get the original 2D MATRIX DATA rather than the original image. I saved this figure as a .jpg file and then I want to get the raw 2D MATRIX DATA from this .jpg file according to its colormap.
For example, a certain element in the raw MATRIX DATA is 0.5, and it was mapped to a rgb value of (0.3,0.5,0.8) in the saved .jpg file according to the 'jet' colormap. My purpose is to obtain 0.5 from the rgb value (0.3,0.5,0.8) according to the jet colormap.


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