Why does a second call to IMPIXEL clear my figure and not show previously selected points in the Image Processing Toolbox 7.2 (R2011a) ?

I am using IMPIXEL to select a point. Then when I call IMPIXEL again, the previously selected point is not shown in the figure.

Answer 1

[MathWorks Support Team]

The IMPIXEL function clears the figure once the points have been selected and you hit the Enter key. The function does not currently provide the functionality to keep previously selected points.

In order to get such functionality, a possible workaround would be to implement the functionality using a function like GINPUT or GETPTS along with IMSHOW. You can refer to the sample MATLAB script that I have written below to help you:

clc;

clear all;

close all;

% initialize number of points

np = 1;

% read sample image

img = imread('cameraman.tif');

% display image

imshow(img);

title('Click on an UPPER point');

hold on;

% get coordinates and intensity of selected point

[x,y] = ginput(1);

intensity1 = img(round(x),round(y));

% plot selected point

plot(x,y,'r+');

hold on;

% place text on image

text(x,y,['  \color{blue}' num2str(np)],'FontWeight','bold');

% change title

title('Click on matching LOWER point');

% update np

np = np+1;

% get coordinates and intensity of selected point

[x,y] = ginput(1);

intensity2 = img(round(x),round(y));

% plot selected point

plot(x,y,'r+');

hold on;

% place text on image

text(x,y,['  \color{blue}' num2str(np)],'FontWeight','bold');