How to find the wavelength from a given photo?

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Pijush 2017-12-8

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https://ww2.mathworks.cn/matlabcentral/answers/371923-how-to-find-the-wavelength-from-a-given-photo

评论： Image Analyst 2017-12-11

I want to find the wave-length of few spectral lines like the picture below

Is it possible since i want to use these kind of pictures to find wave length and use those wavelength for using in formulas.

I don't have any other software other than mathlab like simulink.

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Pijush 2017-12-8

no its just a image from Wikipedia. I just want a approximate value so that what ever image i use i can get a wavelength from it and i don't have to put them manually. @starStrider

Star Strider 2017-12-8

That’s a nonstandard format (.svg), at least for MATLAB. When I tried to load it with imread, it threw an error.

Image Analyst may have some thoughts...

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回答（1 个）

Image Analyst 2017-12-8

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https://ww2.mathworks.cn/matlabcentral/answers/371923-how-to-find-the-wavelength-from-a-given-photo#answer_295392

在 MATLAB Online 中打开

You'd have to know what column corresponds to what wavelength. For example, is column 1 defined to be 400 nm and the last column is 700 nm? If so, you can just basically take the column, turn it into a percentage of the way from left to right, then multiply by 300 (=700-400) and add 400.

[rows, columns, numberOfColorChannels] = size(rgbImage);
allColumns = 1 : columns;
wavelength = (700-400) * allColumns / columns + 400;

To get the wavelength at some particular column, say column 250, just do

wavelengthAtCol250 = wavelength(250);

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Pijush 2017-12-11

编辑：Pijush 2017-12-11

在 MATLAB Online 中打开

i am getting error on line 2

    invalid constant left hand side of assignment
>>> [1,40,3] = size(rbgImgage);

with a small arrow below the 3

the code i put was

rbgImage = imread ("s.jpg")
[1,40,3] = size(rbgImgage);
allColumns = 1 : 3;
wavelength = (700-400)*allColumns / 300 + 400;
wavelengthAtCol250 = wavelength(450);

and how to implement this code

logicalIndexes = yourImage(1, :, 1) ~= 0;

Image Analyst 2017-12-11

在 MATLAB Online 中打开

Now, I didn't do that, did I? What I did was

[rows, columns, numberOfColorChannels] = size(rgbImage);
allColumns = 1 : columns;

Why did you change it? You can't put constants on the left hand side because size() is going to try to fill up those spots with the values. Also you misspelled rgbImage.

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