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I have two sets of corresponding vectors that I want to compare. The first set of vectors contain pixel intensity values for every frame Int(F), and the second set contain wavelengths of light (wvLngth(F)). From these vectors I want to produce a third vector that is pixel intensity in terms of wavelength Int(wvLngth). The problem is that vectors containing the wavelengths do not start and end at the same wavelength, nor do the wavelengths increase at the same rate.

For example:

int1Data = [1 2 3 4];

int2Data = [5 6 7 8];

wvLngth1Data = [7 9 10 11];

wvLngth2Data = [9 10 11 13];

%I can plot these two together to align them but how can I add them in the way they are plotted?

figure

plot(wvLngth1Data, int1Data);

hold on

plot(wvLngth2Data, int2Data);

%I'd like to produce something like:

intAvg = [1 3.5 4.5 5.5 8]

wvLngthComb = [7 9 10 11 13]

figure

plot(wvLngthComb, intAvg);

I've looked at things to align or interpolate the data, but I don't think I can align my data set just at the start, because the middle or end would be wrong, and I don't need Matlab to interperet what it things the missing points should be either.

Thanks in advance.

James Browne
on 12 Jun 2019

Greetings,

I think I understand what you are after. I used your example data and wrote a script that creates a list of unique wavelength values from both wavelength data vectors, determines the average pixel intensity for each wavelength, assembles the averages in a vector which corrosponds to the vector of unique wavelength values and then plots the result. It would take quite some work to rework the code if you have more than two sets of intensity/wavelength data but it is certainly doable.

Here is what I came up with:

int1Data = [1 2 3 4];

int2Data = [5 6 7 8];

wvLngth1Data = [7 9 10 11];

wvLngth2Data = [9 10 11 13];

%Determine length of wave length data vectors

n = length(wvLngth2Data);

%Initialize count of mathces variable for use in recording indexes

%of matching wave length values and creating unique wavelength value vector

count1 = 1;

count2 = 1;

%Find unique wavelength values

waveTot = [wvLngth1Data,wvLngth2Data];

%Determine total number of wavelength values

nT = length(waveTot);

%Intialize variables to indicate duplicate has been found and if current

%value is a duplicate

dupFound = false;

duplicate = false;

%Find unique wavelength values

for i = 1:nT-1

for j = i+1:nT

if (waveTot(i) == waveTot(j) )

repeatIndices(count1) = j;

count1 = count1 +1;

dupFound = true;

end

end

if (dupFound)

for k = 1:count1 - 1

if ( i == repeatIndices(k) )

duplicate = true;

end

end

end

if(~duplicate)

uniqueWaveVals(count2) = waveTot(i);

count2 = count2 + 1;

end

if( (j == nT) )

duplicate = false;

for k = 1:count1 - 1

if ( i == repeatIndices(k) )

duplicate = true;

end

end

if( ~duplicate )

uniqueWaveVals(count2) = waveTot(j);

end

end

duplicate = false;

end

%Determine number of unique wave length values

nUniques = length(uniqueWaveVals);

%Initialize variables to indicate where a unique waveform appears

foundIn1 = false;

foundIn2 = false;

%Initiate variables for recoding the index at which unique wavelengths are

%found

match1 = 0;

match2 = 0;

%Preallocate memory to store average values

avgIntensities = zeros(1,nUniques);

%Calculate average values for each unique wave form value

for i = 1:nUniques

foundIn1 = false;

foundIn2 = false;

for j = 1:n

if (wvLngth1Data(j) == uniqueWaveVals(i) )

foundIn1 = true;

match1 = j;

end

end

for j = 1:n

if (wvLngth2Data(j) == uniqueWaveVals(i) )

foundIn2 = true;

match2 = j;

end

end

if(foundIn1 && ~foundIn2)

avgIntensities(i) = int1Data(match1);

end

if(~foundIn1 && foundIn2)

avgIntensities(i) = int2Data(match2);

end

if(foundIn1 && foundIn2)

avgIntensities(i) = (int2Data(match2)+int1Data(match1))/2;

end

end

plot(uniqueWaveVals,avgIntensities)

title('Average Pixel Intensity VS Light Wavelength')

xlabel('Wavelength (units)')

ylabel('Average Pixel Intensity (units)')

If this is not quite what you are looking for, I hope that it at least gives you a few good ideas!

Guillaume Erny
on 7 Mar 2021

Edited: Guillaume Erny
on 7 Mar 2021

Hi Jason,

I always use this function when I want to compare spectroscopic date with different axes and it work perfectly

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