Dynamically setting a 'targetSize' for centerCropWindow2d()

Following the example from the documentation page of the centerCropWindow2d function, I am trying to dynamically crop an image based on a 'scale' value that is set by the user. In the end, this code would be used in a loop that would scale an image at different increments, and compare the landmarks between them using feature detection and extraction methods.

I wrote some test code to try and isolate 1 instance of this user-specified image cropping,

file = 'frameCropped000001.png';
image = imread(file);

scale = 1.5;
scaled_width = scale * 900;
scaled_height = scale * 635;
target_size = [scaled_width scaled_height];

scale_window = centerCropWindow2d(size(image), target_size);
image2 = imcrop(image, scale_window);

figure;
imshow(image);

figure;
imshow(image2);

but I am met with this error:

Error using centerCropWindow2d (line 30)
Expected input to be integer-valued.

Error in testRIA (line 20)
scale_window = centerCropWindow2d(size(image), target_size);

Is there no way to do use this function the way I explained above? If not, what's the easiest way to "scale" an image around its center point [that is, if I scale it by 0.5, the image stays the same size but is zoomed in by 2x]?

Thank you in advance.

Answer 1

[Walter Roberson]

Is there no way to do use this function the way I explained above?

scale = 1.5

scale = 1.5000

scaled_width = scale * 900

scaled_width = 1350

scaled_height = scale * 635

scaled_height = 952.5000

You are asking the function to produce an output that is 952 1/2 pixels high, but MATLAB has no way to represent storing half of a pixel. You need to floor() or ceil() the values, depending whether you want 952 or 953 pixels for the result.

[Tamir Melzer-Bronstein]

Totally didn't think of the values of height in width that weren't whole numbers. That solved my issue; thank you very much!