getframe() resizing capture issue

So I am trying to use getframe() to capture a plot of an image and then use that image later as a filter. I have found that if I run this on images over a certain dimension, even though the image is still able to display 100% in the figure window, the getframe() command captures a smaller display than is shown (as given by the cdata matrix). Any help?

close all
figure(1),imshow(im2bw(image_v2,1),'InitialMagnification',100), truesize, hold on, scatter(x,y,30,'ws','MarkerFaceColor',[1 1 1]);
imagemask = getframe();
rgb = imagemask.cdata(:,:,1);
figure(2),imshow(rgb);

dimensions = size(rgb);
rgb(dimensions(1),:)=[];
rgb(:,dimensions(2))=[];
dimensions = size(rgb);

for i = 1:dimensions(1)
    for j = 1:dimensions(2)
        if rgb(i,j)==255
            rgb(i,j)=1;
        elseif rgb(i,j)==1
            rgb(i,j)=0;
        end
    end
end

figure(4), imshow(rgb)
image_filtered = image_v2.*rgb;
figure(3),imshow(image_filtered);

[Walter Roberson]

Could you be more specific about the size limits you are encountering? Also which OS are you using, which MATLAB version, and what monitor size are you using? What does

get(0,'ScreenSize')

show? Also, do you happen to be using multiple monitors?