How to get matrix from plot ???

Question

Mohammad Bhat 2018-2-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/384349-how-to-get-matrix-from-plot

编辑： Jan 2018-2-26

采纳的回答： John BG

Hi,I plotted a CYY and CXX having certain values .....

plot(CYY,CXX,'g*');

Now I want to get those plotted values marked '*' in plot in an matrix, can it be done???

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Jan 2018-2-24

It is still not clear to me, what your inputs are. John BG's solution assumes, that you have an image array of the plot, e.g. as if it is imported by imread. Is this correct? Or do you have the values of CYY and CXX available and want to create the image array e.g. to write it to a PNG file?

Mohammad Bhat 2018-2-24

I have CXX and CYY....

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Answer 1

John BG 2018-2-23

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/384349-how-to-get-matrix-from-plot#answer_306793

Hi Mohammad

This is John BG <mailto:jgb2012@sky.com jgb2012@sky.com>

1.

Allow me to start with the same image you have supplied op.jpg

close all;clc;clear all
input_image='001.jpg';
A=imread(input_image);
figure(1);imshow(A);

.

Attached both start image and script to help reproduce result.

.

2. Amplify the image to avoid some too close stars overlapping and then alias would happen

.

Ar=imresize(A,20);

.

3. Green minus Blue shows a good response to blur a bit the starts yet keeping sharpness of each peak

.

A21=Ar(:,:,2)-Ar(:,:,3); % green - blue
figure(2);h1=imshow(A21);

.

4. Comment, at this point imcontrast can be used to show what range of pixel values are most useful

.

imcontrast(h1); % thresholds 59 and 123

.

instead one can manually perform the same pixel selection without imcontrast

th1=100;th2=59;  
A21(A21<th2)=0;
A21(A21>=th1)=255;
figure(3);imshow(A21);

.

5. Reducing the size of the image a bit to save time i next step finding 2D peaks

.

A2=imresize(A21,.1);
figure(4);imshow(A2);

6.

Use Natan's function FastPeakFind.m available here:

https://www.mathworks.com/matlabcentral/fileexchange/37388-fast-2d-peak-finder?s_tid=srchtitle

.

      pk3=FastPeakFind(A2);
      figure(5);imagesc(A2); hold on
      figure(5);plot(pk3(1:2:end),pk3(2:2:end),'r+')

.

7.

FastPeakFind returns a single file list of coordinates that are the [x y] coordinates interleaved, to obtain the paired coordinates:

x_peak=pk3(1:2:end);
y_peak=pk3(2:2:end);
p_stars=[x_peak y_peak];

8.

The amount of stars found is:

size(p_stars,1)
ans =
   152

Mohammad

if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance for time and attention

John BG

<mailto:jgb2012@sky.com jgb2012@sky.com>

A couple additional comments:

9.1. tried *imfindcircles* but all tested parameters did not return any result as close as the previous steps.
[centers, radii, metric] = imfindcircles(A21,[8 15],'ObjectPolarity','bright','Sensitivity',.94);
[centers, radii, metric] = imfindcircles(A21,[15 31],'Method','PhaseCode','ObjectPolarity','bright','Sensitivity',.94);
radii=floor(radii);
viscircles(centers, radii,'EdgeColor','r');
9.2. tried *findpeaks2.m* available from here:
% https://www.mathworks.com/matlabcentral/fileexchange/46806-findpeaks2-m?s_tid=srchtitle
% [pk2,id2]=findpeaks2(A2);

2 minutes waiting and still busy.

radiiStrong5 = radii(1:5);
metricStrong5 = metric(1:5);
viscircles(centers, radii,'EdgeColor','r');

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John BG 2018-2-24

Hi Mohammad

the key point that other readers of your question did not understand was that you start with the plot only, not the location of the points: getting the points is the objective.

Because of the way you simulate the data, with

plot(CYY,CXX,'g*')

they assumed that because you already had the data of interest, all you had to do is to pull it back, let me explain:

this

plot(CYY,CXX,'g*')

is the same as

h=plot(CYY,CXX,'g*')

Let's say that you have the following CYY CXX:

h=plot([1:1:10],[2:2:20])

h is a handle to the plot containing the following:

AlignVertexCenters: 'off'
            Annotation: [1×1 matlab.graphics.eventdata.Annotation]
          BeingDeleted: 'off'
            BusyAction: 'queue'
         ButtonDownFcn: ''
              Children: [0×0 GraphicsPlaceholder]
              Clipping: 'on'
                 Color: [1×3 double]
             CreateFcn: ''
             DeleteFcn: ''
           DisplayName: ''
      HandleVisibility: 'on'
               HitTest: 'on'
         Interruptible: 'on'
              LineJoin: 'round'
             LineStyle: '-'
             LineWidth: 0.500000000000000
                Marker: 'none'
       MarkerEdgeColor: 'auto'
       MarkerFaceColor: 'none'
         MarkerIndices: [1 2 3 4 5 6 7 8 9 10]
            MarkerSize: 6
                Parent: [1×1 Axes]
         PickableParts: 'visible'
              Selected: 'off'
    SelectionHighlight: 'on'
                   Tag: ''
                  Type: 'line'
         UIContextMenu: [0×0 GraphicsPlaceholder]
              UserData: []
               Visible: 'on'
                 XData: [1 2 3 4 5 6 7 8 9 10]
             XDataMode: 'manual'
           XDataSource: ''
                 YData: [2 4 6 8 10 12 14 16 18 20]
           YDataSource: ''
                 ZData: [1×0 double]
           ZDataSource: ''

if you key in

h.XData
h.YData
 =
  Columns 1 through 9
     1     2     3     4     5     6     7     8     9
  Column 10
    10
 =
  Columns 1 through 9
     2     4     6     8    10    12    14    16    18
  Column 10
    20

you get back the data used to plot.

But you clarified that you don't have this data, this precisely what we are after.

Without the locations of the points one cannot plot.

Function plot doesn't start unless you supply the precise locations of each point to plot, no guessing: no points? no plot.

But if you already have the location of the points there wouldn't be any need to ask the question, would it?

You added the comment to a now deleted attempted answer that all you had as start point is the plotting itself, probably the actual print-out or a .pdf file or .jpg with the resulting graph, but not the precise coordinates, and that is exactly what you need.

If instead of capturing the handle of the plot you choose to capture the handle to the axes,

 ax=gca
                         ALim: [0 1]
                     ALimMode: 'auto'
       ActivePositionProperty: 'outerposition'
            AmbientLightColor: [1 1 1]
                 BeingDeleted: 'off'
                          Box: 'on'
                     BoxStyle: 'back'
                   BusyAction: 'queue'
                ButtonDownFcn: ''
                         CLim: [0 1]
                     CLimMode: 'auto'
               CameraPosition: [1×3 double]
           CameraPositionMode: 'auto'
                 CameraTarget: [5.500000000000000 11 0]
             CameraTargetMode: 'auto'
               CameraUpVector: [0 1 0]
           CameraUpVectorMode: 'auto'
              CameraViewAngle: 6.608610360311923
          CameraViewAngleMode: 'auto'
                     Children: [1×1 Line]
                     Clipping: 'on'
                ClippingStyle: '3dbox'
                        Color: [1 1 1]
                   ColorOrder: [7×3 double]
              ColorOrderIndex: 2
                    CreateFcn: ''
                 CurrentPoint: [2×3 double]
              DataAspectRatio: [4.500000000000000 9 1]
          DataAspectRatioMode: 'auto'
                    DeleteFcn: ''
                    FontAngle: 'normal'
                     FontName: 'Helvetica'
                     FontSize: 10
                FontSmoothing: 'on'
                    FontUnits: 'points'
                   FontWeight: 'normal'
                    GridAlpha: 0.150000000000000
                GridAlphaMode: 'auto'
                    GridColor: [1×3 double]
                GridColorMode: 'auto'
                GridLineStyle: '-'
             HandleVisibility: 'on'
                      HitTest: 'on'
                Interruptible: 'on'
      LabelFontSizeMultiplier: 1.100000000000000
                        Layer: 'bottom'
                       Legend: [0×0 GraphicsPlaceholder]
               LineStyleOrder: '-'
          LineStyleOrderIndex: 1
                    LineWidth: 0.500000000000000
               MinorGridAlpha: 0.250000000000000
           MinorGridAlphaMode: 'auto'
               MinorGridColor: [1×3 double]
           MinorGridColorMode: 'auto'
           MinorGridLineStyle: ':'
                     NextPlot: 'replace'
                OuterPosition: [0 0 1 1]
                       Parent: [1×1 Figure]
                PickableParts: 'visible'
           PlotBoxAspectRatio: [1×3 double]
       PlotBoxAspectRatioMode: 'auto'
                     Position: [1×4 double]
                   Projection: 'orthographic'
                     Selected: 'off'
           SelectionHighlight: 'on'
                   SortMethod: 'childorder'
                          Tag: ''
                      TickDir: 'in'
                  TickDirMode: 'auto'
         TickLabelInterpreter: 'tex'
                   TickLength: [1×2 double]
                   TightInset: [1×4 double]
                        Title: [1×1 Text]
      TitleFontSizeMultiplier: 1.100000000000000
              TitleFontWeight: 'bold'
                         Type: 'axes'
                UIContextMenu: [0×0 GraphicsPlaceholder]
                        Units: 'normalized'
                     UserData: []
                         View: [0 90]
                      Visible: 'on'
                        XAxis: [1×1 NumericRuler]
                XAxisLocation: 'bottom'
                       XColor: [1×3 double]
                   XColorMode: 'auto'
                         XDir: 'normal'
                        XGrid: 'off'
                       XLabel: [1×1 Text]
                         XLim: [1 10]
                     XLimMode: 'auto'
                   XMinorGrid: 'off'
                   XMinorTick: 'off'
                       XScale: 'linear'
                        XTick: [1 2 3 4 5 6 7 8 9 10]
                   XTickLabel: {10×1 cell}
               XTickLabelMode: 'auto'
           XTickLabelRotation: 0
                    XTickMode: 'auto'
                        YAxis: [1×1 NumericRuler]
                YAxisLocation: 'left'
                       YColor: [1×3 double]
                   YColorMode: 'auto'
                         YDir: 'normal'
                        YGrid: 'off'
                       YLabel: [1×1 Text]
                         YLim: [2 20]
                     YLimMode: 'auto'
                   YMinorGrid: 'off'
                   YMinorTick: 'off'
                       YScale: 'linear'
                        YTick: [1×10 double]
                   YTickLabel: {10×1 cell}
               YTickLabelMode: 'auto'
           YTickLabelRotation: 0
                    YTickMode: 'auto'
                        ZAxis: [1×1 NumericRuler]
                       ZColor: [1×3 double]
                   ZColorMode: 'auto'
                         ZDir: 'normal'
                        ZGrid: 'off'
                       ZLabel: [1×1 Text]
                         ZLim: [-1 1]
                     ZLimMode: 'auto'
                   ZMinorGrid: 'off'
                   ZMinorTick: 'off'
                       ZScale: 'linear'
                        ZTick: [-1 0 1]
                   ZTickLabel: ''
               ZTickLabelMode: 'auto'
           ZTickLabelRotation: 0
                    ZTickMode: 'auto'

from the axes handle you can pull the figure handle

hf=ax.Parent

a broader structure wrapped around the data.

Or again read the data:

ax.Children.XData
 =
  Columns 1 through 9
     1     2     3     4     5     6     7     8     9
  Column 10
    10
ax.Children.YData
 =
  Columns 1 through 9
     2     4     6     8    10    12    14    16    18
  Column 10
    20

Now you can see that plot handles, axes handles, and figure handles deliver more or less complex structures that are really useful when solving problems, but in essence they are all wrapped around the critical crucial data, the lack of which originated the question, if we already have the data, no need to ask for the data, right?

Hope it helps, all the best

John BG

<mailto:jgb2012@sky.com jgb2012@sky.com>

John BG 2018-2-25

the sentence

I have computed CXX and CYY by some croteria aftet ploting I am getting desired figure or graph

means that the points are probably on a piece of paper, or scanned file.

Mohammad has the points, on the map, paper, but want the MATLAB matrix. HEADLINE OF THE QUESTION:

How to get matrix from plot ?

Why would any one be asking for the matrix if the matrix is already available, precisely to use the MATLAB function plot?

I don't know you, but I am not aware of any plotting command, in MATLAB or for the case in any programming language, plotting that guesses data to plot When No Such Data Has Been Yet Supplied.

For the record, to me those green stars look like street lamp posts along roads, the positions have probably been marked with a marker on paper and now, obviously, further processing is needed, and MATLAB is the perfect tool, but Mohammad asks the question, because?

How to get matrix from plot ?

Ist es jetz klar?

Viele Gruße