How to create a bounding box in webcam preview and capture image in that bounding box?

This is how I want to do it:

1. Determine positions in webcam preview

2. Create bounding box on that positions in webcam preview

3. Place hand in bounding box

4. Capture it

Answer 1

[Image Analyst]

You can use ginput, rectangle(), imrect() or other functions to determine locations in the image. Then use plot() to create the box. Then call getsnapshot, which will get the full image but you then crop it with imcrop() to limit it to just the bounding box.

[Explorer]

vid = videoinput('winvideo');

preview(vid);

[x y w h] = [128.5 127.5 311 381]

plot(rectangle, axes[128.5 127.5 311 381])

Something is wrong with plotting ......don't know what

[Image Analyst]

Look up how to use plot. axes() is a function and is not followed by square brackets. rectangle is also a function, so you don't do that either. You need to pass in the x and y coordinates (5 each) for the corners of the box

x = [x1, x2, x2, x1, x1];
y = [y1, y1, y2, y2, y1];
hold on;
plot(x, y, 'LineWidth', 2);

[Explorer]

vid = videoinput('winvideo');

preview(vid);

hold on

thisBB = [128.5 127.5 311 381]

rectangle('Position', [thisBB(1),thisBB(2),thisBB(3),thisBB(4)],... 'EdgeColor','r','LineWidth',2 )

This logic is okay for image but not working for live webcam preview. Please do necessary change to make it work.

[Image Analyst]

Try this:

% Create axes control.
handleToAxes = axes();
% Get the handle to the image in the axes.
hImage = image(zeros(480,640,'uint8'));
% Reset image magnification. Required if you ever displayed an image
% in the axes that was not the same size as your webcam image.
hold off;
axis auto;
axis on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);

% Turn on the live video.
videoObject = videoinput('winvideo');
preview(videoObject, hImage);
hold on
thisBB = [28.5 27.5 311 381]
rectangle('Position', [thisBB(1),thisBB(2),thisBB(3),thisBB(4)], 'EdgeColor','r','LineWidth',2 )

[Alvaro Poblacion]

This solution indeed plots the rectangle on the webcam preview, but Matlab crashes if I try to close the preview!

[Walter Roberson]

Alvaro : you need to stop the preview before you close the window.

See also https://www.mathworks.com/matlabcentral/answers/153296-how-can-you-stop-live-video-from-playing-in-the-gui

[Patrick Tichelmann]

OK, this plots a rectangle on the video but how can I get the image of the frame? I want to take an image all n-seconds of the frame. How can i do that?

[Image Analyst]

Try the function getsnapshot(). It's what I use, but that is with a machine vision camera and the Image Acquisition Toolbox, not the webcam support software, but it might work - try it.

[Explorer]

@ Image Analyst

% Create axes control.
handleToAxes = axes();
% Get the handle to the image in the axes.
hImage = image(zeros(480,640,'uint8'));
% Reset image magnification. Required if you ever displayed an image
% in the axes that was not the same size as your webcam image.
hold off;
axis auto;
axis on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Turn on the live video.
videoObject = videoinput('winvideo');
preview(videoObject, hImage);
hold on
thisBB = [28.5 27.5 311 381]
rectangle('Position', [thisBB(1),thisBB(2),thisBB(3),thisBB(4)], 'EdgeColor','r','LineWidth',2 )

This code is not working properly in MATLAB R2015b. The webcam preview seems magnified than normal. There are problems in screen size. Could you please modify it to make it compatible with MATLAB version of 2015.

[Image Analyst]

I think you might be using only the central 480x640 part of your camera sensor, which might be larger, like 1980x1080 if it's a (still low res) HDTV resolution.

Can you tell me what this command shows:

imaqhwinfo

[Explorer]

ans =

    InstalledAdaptors: {'dcam'  'winvideo'}
    MATLABVersion: '8.6 (R2015b)'
    ToolboxName: 'Image Acquisition Toolbox'

After replacing 480x640 with 980x1080, webcam preview appears as follows.

[Image Analyst]

Can you run imaqtool? If so, in the upper left panel, what size mode options do you see for the various adapters?

See attached webcam demo. You might have to change the webcam name from Logitech to whatever you have.

[Explorer]

This is what I am getting after running imaqtool.

I am unable to understand your attached codes.

[Image Analyst]

Can you try720 rows by 1280 columns?

[Explorer]

Yes, it is working perfectly. Thank you Image Analyst.

[Heloise BOTREL]

%Set up
clear all, close all
webcamlist;
mycam=webcam;

%Visualisation

% Create axes control.
handleToAxes = axes();
% Get the handle to the image in the axes.
hImage = image(zeros(480,640,'uint8'));
% Reset image magnification. Required if you ever displayed an image
% in the axes that was not the same size as your webcam image.
hold off;
axis auto;
axis on;
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Turn on the live video.
videoObject = videoinput('winvideo');
preview(videoObject, hImage);
hold on
thisBB = [28.5 27.5 311 381]
rectangle('Position', [thisBB(1),thisBB(2),thisBB(3),thisBB(4)], 'EdgeColor','r','LineWidth',2 )

This code return :

Error using videoinput (line 532)
winvideo: Image acquisition device is not
accessible.
Insufficient system resources exist to complete the
requested service.
Make sure no other objects or applications are
accessing the same device.

Error in helo (line 20)
videoObject = videoinput('winvideo');

Do you have any idea to resolve it ?

[Image Analyst]

Did you install the webcam add-on? See the Add-ons tab. Home->Addons-> Get Addons -> MATLAB support package for USB webcams.

What does this show:

webcamlist % No semicolons.
mycam=webcam

[Heloise BOTREL]

Ans :

webcamlist % No semicolons.
mycam=webcam

ans =

  1×1 cell array

    {'HP TrueVision HD'}


mycam = 

  webcam with properties:

                     Name: 'HP TrueVision HD'
     AvailableResolutions: {1×6 cell}
               Resolution: '640x480'
                 Exposure: -6
                Sharpness: 2
                     Gain: 4
                 Contrast: 32
             WhiteBalance: 4000
               Saturation: 64
                      Hue: 0
                    Gamma: 120
             ExposureMode: 'auto'
               Brightness: 128
    BacklightCompensation: 1
         WhiteBalanceMode: 'auto'

I have this package and "Image Acquisition Toolbox Support Package for OS generic Video Interface" and 'Image Acquisition Toolbox"

Answer 2

[Aude Menet]

Error using videoinpu (line 219)
Invalid ADAPTATORNAME specified. Type 'imaqhwinfo' for a list of available 
ADAPTORNAMEs. Image acquisition adaptors may be available as downloadable 
support packages. Open Add-Ons Explorer to install additional adaptors.

Error in cameratest (line 20)
videoObject=videoinput('winvideo');

Can someone help me to fix these errors please ?

[Image Analyst]

What does this show for you?

>> imaqhwinfo

ans =

struct with fields:

InstalledAdaptors: {'winvideo'}

MATLABVersion: '9.8 (R2020a)'

ToolboxName: 'Image Acquisition Toolbox'

ToolboxVersion: '6.2 (R2020a)'

and this:

webcamlist % No semicolons.
mycam=webcam

ans =

1×1 cell array

{'Integrated Webcam'}

mycam =

webcam with properties:

Name: 'Integrated Webcam'

AvailableResolutions: {'1280x720' '960x540' '848x480' '640x480' '640x360' '424x240' '320x240' '320x180' '160x120'}

Resolution: '1280x720'

WhiteBalanceMode: 'auto'

Saturation: 64

Exposure: -6

Gain: 1

Hue: 0

Gamma: 100

Sharpness: 2

WhiteBalance: 4600

Brightness: 0

Contrast: 0

ExposureMode: 'auto'

BacklightCompensation: 3

[Aude Menet]

Thank you for this quick answer!

So

>> imaqhwinfo

returns me :

Warning : No Image Acquisition adaptors found. Image acquisition adaptors may be available as downloadable support packages. Open Add-Ons Explorer to install additional adaptors.

ans =

struct with fields :

InstalledAdaptors: {}

MATLABVersion: '9.3 (R2017b)'

ToolboxName: 'Image Acquisition Toolbox'

ToolboxVersion: '5.3 (R2017b)'

And this

webcamlist %No semicolons.
mycam=weblist

returns

ans =

1x1 cell array

{'Caméra Facetime HD'}

mycam =

webcam with properties:

Name: 'Caméra FaceTime HD'

Resolution: '1280x720'

AvailableResolutions: {'1280x720'}

[Image Analyst]

Have you downloaded the webcam add on? Use the Add-Ons explorer from the Home tab of the tool ribbon and type in webcam.

[Aude Menet]

Yes I have dowloaded them since I'm trying to make my webcam work through matlab.

Answer 3

[Image Analyst]

When you do this, do you get a live video window that pops up? I do

webcamlist
mycam = webcam
methods(mycam)
mycam.preview

[Aude Menet]

Yes I do, it works well !

[Image Analyst]

Now try the snapshot() method:

% Display a list of installed cameras.
webcamlist
% Get an object linked to the webcam.
mycam = webcam
% Show what things this camera can do
methods(mycam)
properties(mycam)
% Open live video window.
mycam.preview
% Prompt user to snap a photo.
promptMessage = sprintf('Do you want to snap a photo,\nor Quit?');
titleBarCaption = 'Continue?';
buttonText = questdlg(promptMessage, titleBarCaption, 'Snap', 'Quit', 'Snap');
if contains(buttonText, 'Quit', 'IgnoreCase', true)
	return;
end
% Snap the photo.
rgbImage = mycam.snapshot;
% Close live video window.
mycam.closePreview
% Display image
imshow(rgbImage);
caption = sprintf('Here is the photo you snapped at %s', datestr(now));
title(caption, 'FontSize', 20);
% Maximize figure.
g = gcf;
g.WindowState = 'maximized';