problem in connecting with webcam and re

I use this code to take a picture but the picture is very eliminate.but also when I use this command "preview(cam)" on time image is good. what is the problem with the picture?the code is below

cam=videoinput('winvideo' , 2);
set(cam.source , 'Brightness' , 240);
pic=getsnapshot(cam);

[Walter Roberson]

Sorry I did not catch what you meant by "very eliminate" ?

Are you displaying the image after you snapshot it?

Could you post some examples?

[Behrad kiani]

it is too dark.this is a pic from my face

[Walter Roberson]

I would not assume that the default video format is RGB. You should find out which formats your camera can return, and select one specifically. Then if necessary, convert colorspaces into something you can display. If the video format is grayscale, make sure you have a grayscale colormap active when you display it.

[Behrad kiani]

imaqhwinfo('winvideo' , 2)

ans =

          DefaultFormat: 'YUY2_160x120'
    DeviceFileSupported: 0
             DeviceName: 'A4TECH USB2.0 PC Camera'
               DeviceID: 2
      ObjectConstructor: 'videoinput('winvideo', 2)'
       SupportedFormats: {1x5 cell}

>> cam = videoinput('winvideo') >> imaqhwinfo(cam)

ans =

                AdaptorName: 'winvideo'
                 DeviceName: 'Integrated Webcam'
                  MaxHeight: 720
                   MaxWidth: 1280
             NativeDataType: 'uint8'
               TotalSources: 1
    VendorDriverDescription: 'Windows WDM Compatible Driver'
        VendorDriverVersion: 'DirectX 9.0'

Answer 1

[Image Analyst]

Do you have a weird colormap applied? Is the camera running in monochrome mode? Your videoinput() code doesn't look like mine. Mine looks like:

    % Initialize Logitech webcam
    vidobj = videoinput('winvideo', 1, 'RGB24_640x480');
    if ~isempty(vidobj)
      src = getselectedsource(vidobj);
      vidobj.FramesPerTrigger = 1;
      axes(handles.axesImage);
      hImage = findobj(handles.axesImage, 'Type', 'image');
      preview(vidobj, hImage);
    %       src.ZoomMode = 'manual';
      % Turn on the live video preview.  Display the bounding box over it if there is one selected.
      TurnOnLiveVideo(handles); % My own function
    end

Are you sure you're supposed to be using camera #2? Why did you not specify an operation mode, such as 'RGB24_640x480', for the video?

[Behrad kiani]

imaqhwinfo('winvideo' , 2)

ans =

          DefaultFormat: 'YUY2_160x120'
    DeviceFileSupported: 0
             DeviceName: 'A4TECH USB2.0 PC Camera'
               DeviceID: 2
      ObjectConstructor: 'videoinput('winvideo', 2)'
       SupportedFormats: {1x5 cell}

>> cam = videoinput('winvideo') >> imaqhwinfo(cam)

ans =

                AdaptorName: 'winvideo'
                 DeviceName: 'Integrated Webcam'
                  MaxHeight: 720
                   MaxWidth: 1280
             NativeDataType: 'uint8'
               TotalSources: 1
    VendorDriverDescription: 'Windows WDM Compatible Driver'
        VendorDriverVersion: 'DirectX 9.0'

[Walter Roberson]

Tell us what output you get from

T = imaqhwinfo('winvideo' , 2);
T.SupportedFormats

Your data is currently being collected in YUY2 format, which is one of the reasons that your image comes out wrong.

[Behrad kiani]

 Columns 1 through 3

    'YUY2_160x120'    'YUY2_176x144'    'YUY2_320x240'

Columns 4 through 5

    'YUY2_352x288'    'YUY2_640x480'

[Walter Roberson]

Odd, your camera can do 720 x 1280, but the largest format returned is 640 x 480.

Anyhow, you should activate that format. And then you need to decide what you want to do with the data returned.

I suggest that you read the comments for http://www.mathworks.com/matlabcentral/fileexchange/26249-yuy2-to-rgb-converter

[Behrad kiani]

but why preview(cam) gives me a good image

[Walter Roberson]

I do not know.

[Image Analyst]

I don't know why there are non-RGB modes in the first place. I only use cameras in RGB mode so I don't really know why, when, or how you'd use non-RGB modes. Since computers only display RGB I don't know if the R is the Y channel and the G is the U channel and the B is the V channel or it's some other arrangement, or if it's somehow converted internally. These would be good questions to ask the Mathworks. Or else just get a camera than can handle RGB.

[Walter Roberson]

The comments in the link I posted show how to get the YUY2 space converted to RGB.

[Image Analyst]

Thanks. I forgot. Another good answer from David on the Image Acquisition team: http://www.mathworks.com/matlabcentral/answers/75519#answer_85238