How can I add a histogram to a live video preview?

Hi I'm working on a project where I've created a custom GUI and connected the axes (axes1) to an external camera when a button is pushed and on the same button push a live histogram of the preview image should come up in a different axes. I have gotten the preview to appear and the histogram to appear, however, the histogram does not update itself automatically when the preview image is changed. I've tried everything and need a direction to go on with this. Here's my code below for just the button I'm trying to get working:

 function pushbutton1_Callback(hObject, eventdata, handles)

 handles = guidata(hObject);

 imaqmex('feature', '-previewFullBitDepth', true);
 axes(handles.axes1)
 vid = videoinput('Camera_source_1', 1, 'MONO16_BIN2x2_1024x1024_SlowMode');
 src = getselectedsource(vid);
 vidres = vid.VideoResolution;
 imWidth = vidres(1);
 imHeight = vidres(2);
 nBands = vid.NumberOfBands;
 himage = image(zeros(imHeight,imWidth, nBands), 'Parent', handles.axes1);

 figSize = get(handles.axes1, 'Position');
 figWidth = figSize(3);
 figHeight = figSize(4);
 gca.unit = 'pixels';
 gca.position = [((figWidth - imWidth)./2)...
                ((figHeight - imHeight)./2)...
                imWidth imHeight];

 vid.FramesPerTrigger = Inf;
 src.ExposureTime = user_val(1);

 im = preview(vid, himage);
 ax = im.Parent;
 im.CDataMapping = 'scaled';
 colormap(ax, gray);
 signalRange = [30 2000];
 ax.CLim = signalRange;

 axes(handles.axes2)

 himage.CData = im.CData;
 set(himage, 'CData', im.CData);
 imhist(himage.CData, 128)
 grid on
 grid minor
 drawnow

 preview(vid, himage)
 guidata(hObject, handles);

Answer 1

[Image Analyst]

I think you're going to have to get a snapshot with getsnapshot() and then histogram that.

[Paul Jacobs]

So I tried implementing this function and it seems effective at getting me the data to plot the initial histogram but the main issue is still once I have the data from getsnapshot() and then I try changing the previewed image, the histogram doesn't update to the new image. I've tried using

setappdata(himage,'UpdatePreviewWindowFcn',@update_livehistogram_display);

And this function does give me a live updated histogram, however, it appears in a separate window and when I go to press another button in the GUI it glitches and doesn't work. The specific code for that 'update_livehistogram_display' is below:

 function update_livehistogram_display(obj,event,himage)   

     himage.CData = event.Data;
     set(himage, 'CData', event.Data);
     imhist(himage.CData, 128)
     grid on
     grid minor
     drawnow

     end
  end

[Image Analyst]

I think you might have to not use preview and just have getsnapshot() and imhist() in a loop. So it's not "live" anymore but a series of snapshots, hopefully the histogramming won't slow it down too much and it will look "live". You might want to do the histogram only every 10 snapshots or so to speed it up.

[Paul Jacobs]

Ok so I put in a for loop around the portion that gets the snap shot and plots it as a histogram as seen below:

 axes(handles.axes2)
 for I = 1:1:10000
 frame_test_data = getsnapshot(vid);
 himage.CData = frame_test_data;
 set(himage, 'CData', frame_test_data);
 imhist(himage.CData, 128)
 grid on
 grid minor
 drawnow
 end

Now the only issue I'm still having is that it interferes with another button being pushed saying: "Reference to non-existent field 'vid'" Vid being my video object that I'm trying to reference to do auto-contrasting in the preview window.