Read the screen value according to the colorbar

Question

bozheng 2023-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/2050067-read-the-screen-value-according-to-the-colorbar

回答： Image Analyst 2023-11-21

i have a picture with color bar and now we can see blue square if i want collect (For example the second picture) i only write

img1 = imread('10245.jpg');

img = 1*double(img1)

but data show 100 90 120 and so on.... how i should do

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Answer 1

Walter Roberson 2023-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/2050067-read-the-screen-value-according-to-the-colorbar#answer_1357052

在 MATLAB Online 中打开

img1 = imread('10245.jpg');
img = im2double(img1);

However, the result is going to be a 3D array (RGB) with entries in the range 0 to 1. It is not going to be an intensity image with values in the range 0 to 1.

It looks like the colormap might be parula. You could experiment with

img1 = imread('10245.jpg');
intens_img = rescale(rgb2ind(img1, parula), 0, 1, 'InputMin', 0, 'InputMax', 255);

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Answer 2

Image Analyst 2023-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/2050067-read-the-screen-value-according-to-the-colorbar#answer_1357357

If you are really starting with an RGB image of an indexed image that has been pseudocolored with a colormap, then you will need to "undo" the colormap to get back to the original values. See my File Exchange entry where I get the actual temperature image (floating point numbers in degrees Celsius) from a pseducolored RGB image.

https://www.mathworks.com/matlabcentral/fileexchange/113995-thermal-image-color-to-temperature?s_tid=srchtitle