ImpixelInfo equivalent for Appdesigner

Hello, I am trying to create the same effect as impixelinfo in GUIDE in appdesigner. I understand thereis no such function for appdesigner, so I have created the ImageButtonDownCallback.

function ImageButtonDownCallback(app, source, eventargs)
%Delete any previous annoations, graphics on the image
delete(findobj(app.UIAxes, 'Marker', '*')); %Delete previous marker
delete(findobj(app.UIAxes, 'Marker', '.')); %Delete previous marker
delete(findobj(app.UIAxes, 'Type','rectangle')); %Delete previous rectangler
delete(findobj(app.UIAxes, 'Type','text')); %Delete previous text

%Get current mouse position
z=app.UIAxes.CurrentPoint;
x=round(z(1,1)); y=round(z(1,2));

%Show on the image where the point is
hold(app.UIAxes,'on');
plot(app.UIAxes,x,y,'b*');
drawnow;

%Get the image data so can peform basic stats around the selected point
I=double(getimage(app.UIAxes));

%Now get mean of square small region centred on x,y
delta=100;
ROI = I(y-delta:y+delta, x-delta:x+delta);
mn=mean(ROI(:));
mx=max(ROI(:));

%Report out the values (this is a seperate function that reports to a textarea)
ReportMessage1(app,['x=',sprintf('%.0f',x),', y=',sprintf('%.0f',y),': Mean Intensity=',sprintf('%.0f',mn),', Max = ',num2str(mx)]);

%Draw the ROI rectangle on the image to view
rectangle(app.UIAxes,'Position',[x-delta y-delta 2*delta 2*delta], 'EdgeColor','y','LineWidth',1);
%display the basic stats on the image
text(app.UIAxes,x,y-delta-35,num2str(mn,'%.1f'),'FontSize',16,'Color','r', 'HorizontalAlignment','center');drawnow
hold(app.UIAxes,'off');

%Display the ROI on a seperate axis (UIAxes2) for closer inspection

cla(app.UIAxes2,'reset');
%my autoscale function
n=3
[high,low] = Autoscale1(app,ROI,n);
app.myimage=imshow(ROI,[low,high],'Parent',app.UIAxes2); %image creation

end

I call this callback when I first show the image using:

app.myimage=imshow(frame,[low,high],'Parent',parentAxis); drawnow; %image creation
app.myimage.ButtonDownFcn = @app.ImageButtonDownCallback; %create callback. IMPORTANT: You must use app.****

The issue is sometimes this is quite fast (<1s), but other times it seems to take say 10s.

Is there anything I can do mimic impixelinfo better as this takes <200ms everytime