Curve fitting for 2d Array

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Leostar90 2022-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/1650845-curve-fitting-for-2d-array

评论： Leostar90 2022-2-17

Hi,

I have to find slope by using curve fitting in this figure. There are 7 wavefronts in this image. What method should I apply? I have tried different techniques like I manually selected 2 points and find slope but that is not appropriate way. I have to utilize all the data points and fit curve to all 7 wavefronts. Sample image is attached here

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Answer 1

KSSV 2022-2-16

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If (x,y) are the points of your curve...

m = gradient(y)./gradient(x) ; % diff(y)./diff(x)

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KSSV 2022-2-16

Yes, for the pixel values the positions are (x,y). You need to seek those positions and fit a curve.

Leostar90 2022-2-16

Yes, I am still there.. How to find those positions? m = gradient(y)./gradient(x) ; will this work? if I pass x and y positions? Size of data is 50*1024 double. so If I pass x 1:1024 and y 1:50, that Way I can find gradient of every position.

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Answer 2

yanqi liu 2022-2-16

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https://ww2.mathworks.cn/matlabcentral/answers/1650845-curve-fitting-for-2d-array#answer_897280

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yes，sir，may be choose the target line by color and fit them，such as

im = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/896015/image.png');

jm = rgb2hsv(im);

v = mat2gray(jm(:,:,3));

bw = ~im2bw(v,0.9);

bw2 = imopen(bw, strel('line', 20, 0));

bw3 = logical(bw-bw2);

bw3 = imopen(imclose(bw3, strel('disk', 5)), strel('square', 3));

bw3 = bwareafilt(bw3, 2);

[r,c] = find(bw3);

p = polyfit(c,r,3);

xc = linspace(min(c),max(c));

yc = polyval(p,xc);

figure; imshow(im)

hold on; plot(xc,yc,'r--','LineWidth',2);

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Leostar90 2022-2-16

在 MATLAB Online 中打开

Hi, Thank you for your response.

When I try to run this code then I get this error.

" Error using rgb2hsv>parseInputs (line 95)

MAP must be a Mx3 array.

Error in rgb2hsv (line 36)

[r, g, b, isColorMap, isEmptyInput, isThreeChannel] = parseInputs(varargin{:});

Error in region_seg_demo (line 18)

jm = rgb2hsv(im);

I have data in mat file. So I am just loading mat file and and after accessing value from mat file just passing it to your above mentioned code.

Here is the code too.

clear all,clc
dta = load('C:\Users\Awais\Downloads\Imgaes\Imgaes\region_seg\image.mat');
im=dta.L;
jm = rgb2hsv(im); 
v = mat2gray(jm(:,:,3));
bw = ~im2bw(v,0.9);
bw2 = imopen(bw, strel('line', 20, 0));
bw3 = logical(bw-bw2);
bw3 = imopen(imclose(bw3, strel('disk', 5)), strel('square', 3));
bw3 = bwareafilt(bw3, 2);
[r,c] = find(bw3);
p = polyfit(c,r,3);
xc = linspace(min(c),max(c));
yc = polyval(p,xc);
figure; imshow(im)
hold on; plot(xc,yc,'r--','LineWidth',2);

Leostar90 2022-2-17

did you detect that green line in image or just detected data of that line? I have to apply same curve fitting for all wavefronts in same image? Moreover, I have to find equation of fitted line for finding slope.

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