Figure to movie frame with set size

I'm generating movie frames from figures using the getframe function. However, I need the movie frame matrix output to be of a certain size (a set dimension in pixel units for each frame). I have tried

set(gca,'Units','pixels','Position',[10 10 sizeX sizeY])

But when I export the movie frame the cdata of the frame never seems to be the same size as sizeX and sizeY. There is change in the size of the frame, but it doesn't end up identical.

I know I could just resize the output frames to the size I want, but under some circumstances it resizes away edges and other effects mess up the final result, so it would be preferable if I could get the correct output size directly from the figure.

Answer 1

[Oscar Frick]

Some digging led me to this previously asked question:

https://mathworks.com/matlabcentral/answers/272767-how-to-set-exact-figure-size-in-pixels

And it seems it indeed does have something to do with display scaling. I use a three display setup with two of the displays at 100% scaling (one of which is my designated main display) - but on the third display (the laptop display) I have 125% scaling. I changed the scaling on the laptop display to 100%, and now the example script gives the correct pixel size output. Changing it back, however, the output still stay the same (150 x 100 px). I have tried playing around with the scaling afterwards, but I have not gotten the incorrect scaling to return.

Answer 2

[Image Analyst]

What do you mean by resize and export? You mean "on screen" or the actual image size in pixels? And export how? To a disk file or to a movie variable?

See my movie resizing demo, attached.

[Oscar Frick]

getframe outputs a struct with field cdata and colormap. I need the cdata (matrix) output from getframe to be a certain size, for example 300 x 450 x 3 (the example being a 300x400 px RGB image).

Export might have been a poor choice of word in the context, my point is that when I set the figure axes to be a certain size in pixel, the image frame still comes out the wrong size.

As an example, the following script:

figure(1)
x = 0:0.01:pi;
y = sin(x);
plot(x,y) %just input to give frame some content
set(gca,'Units','pixels','Position', [20 20 100 150])
movieFrame = getframe;

figure(2)
imshow(movieFrame.cdata)

size(movieFrame.cdata)

Gives a movie frame matrix size of 188x125 px, not 150x100 px. I need a way to reliably control the frame size.

As I stated in my original post, I know about the option to resize after having fetched the frame, but due to certain problems with the results it would be preferable to me to omit that step and have the figure be the correct size from the beginning.

Answer 3

[Image Analyst]

Try truesize(), or see the attached demo.

[Oscar Frick]

truesize() and the method in the zoom_image demo works with an already pixelated "figures". Trusize seems to give the same output as imresize() with method 'nearest'.

I'm trying to achieve the resizing before the figure pixelation occurs - i.e. force the built in plot function of matlab to display the plot window of a certain size in pixels.

[Image Analyst]

If I project my image onto a secondary display, my laptop display and the external display will show all pixels on both screens but the physical size will be different because the display is a different size. Are you hoping to control the physical size of the image regardless of the size of the monitor it's displayed on?

[Oscar Frick]

No, what I want to achieve is to control the figure plot area size in such a manner that the getframe() function outputs the figure data to a frame struct with the cdata matrix of a defined size.

It's turns out it's done by setting the gca size in pixel units, just as I tried first, but having monitors with windows scaling involved seem to be messing with it somehow (see my last answer below).

[sam l]

Hi

I have similare issue regarding the figure plot frame size controlling.

I am plotting a figure inside for looop - create a array to store the frame size.

Even I am using the gcf to enter the required frame size, the plot frame size is different and it changes after some steps. The figure plot has 4 subplots - three are in 3D plot..

Could you help if I can get a constant frame size, so I am able to create a vedio animation.

[Image Analyst]

You can call imresize() after you get thisFrame to set it to the exact size you want.

Answer 4

[Eduardo Vicente Wolf Trentini]

I had the same problem as you and finally managed to solve it.

The problem is the camera's field of view.

In this link I comment about:

https://www.mathworks.com/matlabcentral/answers/1731010-how-to-keep-the-same-size-in-figures#answer_1112618

Answer 5

[Arthur]

Yes, display scaling will affect this. In Windows, it's in the settings. I tested that in a remote linux server the size is the one specified using fig.Position, since there's no display. If you want a scaling different from the display scaling, we can do

fig = figure();
frame = getframe(gcf);
img = frame2im(frame);
img = imresize(img, scale);
writeVideo(video, img);