How do I redraw a picture given to me using its data points that I've found using the curve fitting app?

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JoshT_student 2018-6-15

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https://ww2.mathworks.cn/matlabcentral/answers/405855-how-do-i-redraw-a-picture-given-to-me-using-its-data-points-that-i-ve-found-using-the-curve-fitting

评论： DGM 2025-6-30，9:02

Hello, I am trying to redraw this picture given to me by my professor. He told me to analyze it by curve fitting. So I did 4 fits and I was only able to get 3 fits into figures (SEM_data_points_figure, fit_poly2_figure, fit_poly3_fig) The last fit when I tried to save it as a figure kept giving me the error 'Index exceeds array bounds'. However, I need to redraw the picture using the data from these 3 fits. I need help please on how I can write code to go about doing this. Because the professor says I need to write code to get the data.

Thank you for the help.

The code below is from the data points from fit 4 which basically has the same data points as the 3 other fits. The data points for all 4 fits are basically the exact same points.

hold on;

%This is to make the D matrix

D=zeros(300,3);

%These are the data points from my fit poly 4 that I made into matrix form

%However, these cannot go into a matrix.

%How do I display these points in a figure?

D(0,0,0)=1;

D(100,0,0)=1;

D(140,0,0)=1;

D(160,0,0)=1;

D(180,0,0)=1;

D(201,0,0)=1;

D(215,0,0)=1;

D(230,0,0)=1;

D(260,0,0)=1;

imshow(D) %I know this can't work because its for a matrix

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Answer 1

DGM 2025-6-30，0:21

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https://ww2.mathworks.cn/matlabcentral/answers/405855-how-do-i-redraw-a-picture-given-to-me-using-its-data-points-that-i-ve-found-using-the-curve-fitting#answer_1567289

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I don't think anyone needs this answer now, but I came here from a related question that was more interesting, and got caught by how problematically simple this was.

% get the source image

hf = open('SEM_pic.fig');

hi = get(gca,'children');

inpict = hi.CData;

close(hf)

imshow(inpict)

% look at the data and fits

unzip SEM_data_points_figure.zip

hf = open('SEM_data_points_figure.fig'); % the "data"

hl = get(gca,'children');

Xd = hl.XData;

Yd = hl.YData;

Zd = hl.ZData;

close(hf)

unzip fit_poly2_figure.zip

hf = open('fit_poly2_figure.fig'); % fit2 is the same

hl = get(gca,'children');

X = hl.XData;

Y = hl.YData;

Z = hl.ZData;

close(hf)

[isequal(X,Xd) isequal(Y,Yd) isequal(Z,Zd)]

ans = 1×3 logical array

1 1 1

unzip fit_poly3_fig.zip

hf = open('fit_poly3_fig.fig'); % fit3 is the same

hl = get(gca,'children');

X = hl.XData;

Y = hl.YData;

Z = hl.ZData;

close(hf)

[isequal(X,Xd) isequal(Y,Yd) isequal(Z,Zd)]

ans = 1×3 logical array

1 1 1

The sem_data, fit_poly2, and fit_poly3 data are all exactly identical. The Y and Z data are purely zero. The X data contains 1799985 nonzero values, within which, there are only 8 unique values, all of which are integers apparently on uint8-scale.

The image was a 815x1630x3 PNG, the exact same number of elements as the data. This appears to be a vectorized copy of the original image, as almost all values are 0 or 255 (it's an antialiased pseudobinary image).

% just reshape the data to form the image??

outpict = reshape(uint8(X),[815 1630 3]);

imshow(outpict) % it looks the same

isequal(inpict,outpict) % it is the same

ans = logical

1

So I don't see any sort of curve fitting or anything going on here. I see an image and three identical vectorized copies of it, stored in different figure files for extra complication. I have no idea what was going on, but that's how you devectorize it, I guess? The fact that it's simple and the data is duplicated suggests to me that OP didn't know and probably wasted a lot of time thinking it was something else. Saved the wrong data? Been there.

This is the thread I'd found curious:

https://www.mathworks.com/matlabcentral/answers/405781-how-can-i-analyze-stl-files-and-then-redraw-them-in-matlab-i-need-to-write-some-code