How to detect wavelength patterns using fft2?

Hello,
I would like to detect these wavelengths (arrow) :

Find my image here : https://amubox.univ-amu.fr/s/2zb7Q3eRdDCyGRD
My idea was to first calculate the fft2 of my image and then use a high-pass filter to cut off the high wavelength (background). Then find the maximum magnitude of my spectrum and get my wavelength. But it didn’t work.
I know that the wavelength should be approximately equal to 2-3mm on my sensor and 10-13mm in reality (due to an optical setup that focuses my image on my camera’s sensor).

clear all;
clc;
close all;

% 1 load image
image_grayscale = im2gray(im2double(imread("path"))); % Charger votre image ici

% 2. Remove salt & Paper
med_grayImage = medfilt2(image_grayscale, [20 20]);

% 3. clean and smooth image using gaussian filter
sigma = 1.5; % STD gaussian filter
filteredImage = imgaussfilt(med_grayImage, sigma);

% FFT2
fft_image = fftshift(fft2(filteredImage));

figure(1)
subplot(1,3,1);
imshow(image_grayscale);
subplot(1,3,2)
imshow(filteredImage);
subplot(1,3,3)
imshow(log(1 + abs(fft_image)), []);

% size l’image
[m, n] = size(image_grayscale);

% scaling pixel/mm
echelle_pixel_par_mm = 5504/24;

%%
H=6.875;
lambda_c = 1.2*H* 70/333;
frequence_critique = 2*pi/lambda_c;

% Set the cut-off frequency of the high-pass filter
frequence_coupure_x = 24/5504 *frequence_critique;
frequence_coupure_y = 24/5504 *frequence_critique ;

% Créer le masque de filtre passe-haut
masque_filtre = ones(m, n);
centre_x = round(n/2);
centre_y = round(m/2);
for i = 1:m
for j = 1:n
distance = sqrt((i – centre_y)^2 + (j – centre_x)^2);
if distance <= frequence_coupure_x * n && distance <= frequence_coupure_y * m
masque_filtre(i, j) = 0;
end
end
end

% Apply the high-pass filter by multiplying the spectrum by the mask
fft_image_filtre = fft_image .* masque_filtre;

% recontructed image
new_image = real(ifft2(ifftshift(fft_image_filtre)));

figure(2)
subplot(2,2,1)
imshow(masque_filtre)
subplot(2,2,2)
imshow(fft_image_filtre)
subplot(2,2,3)
imshow(new_image)
imcontrast

% Calculer la magnitude du spectre filtré
magnitude_spectre_filtre = abs(fft_image_filtre);

% Prendre le carré de la magnitude pour obtenir la PSD
psd = magnitude_spectre_filtre.^2;

% Afficher la PSD en utilisant une échelle logarithmique
figure;
imagesc(log(1 + psd));
colormap(‘jet’);
colorbar;
title(‘Densité Spectrale de Puissance (PSD)’);
xlabel(‘Fréquence spatiale’);
ylabel(‘Fréquence spatiale’);

% Trouver les coordonnées du maximum de la magnitude du spectre filtré
[max_mag, index] = max(magnitude_spectre_filtre(:));
[indice_ligne, indice_colonne] = ind2sub(size(magnitude_spectre_filtre), index);

% Convertir les coordonnées en fréquences spatiales
frequence_x_pixel = (indice_colonne – 1 – n/2) / n;
frequence_y_pixel = (indice_ligne – 1 – m/2) / m;

% Afficher la fréquence spatiale dominante en millimètres
disp([‘La fréquence spatiale pour laquelle vous avez le maximum d”énergie est : (‘, num2str(frequence_x_pixel), ‘ mm^-1, ‘, num2str(frequence_y_pixel), ‘ mm^-1)’]);

Do you know how to correctly get my wavelenght ?
Do you have any advices ?

Thank youHello,
I would like to detect these wavelengths (arrow) :