Resize an image along rows only or columns only in matlab - image

Question

I'm writing a function in matlab to zoom or shrink an image using bicubic interpolation. However, my function resizes an image along both rows and columns. What if I want to enlarge the image along the rows only, or along the columns only? This is my code so far
function pic_new = zoom_image(pic, zoom_value)
actualSize = size(pic);
newSize = max(floor(zoom_value.*actualSize(1:2)),1);
newX = ((1:newSize(2))-0.5)./zoom_value+0.5; %# New image pixel X coordinates
newY = ((1:newSize(1))-0.5)./zoom_value+0.5;
oldClass = class(pic); %# Original image type
pic = double(pic); %# Convert image to double precision for interpolation
if numel(actualSize) == 2
pic_new = interp2(pic,newX,newY(:),'cubic');
end
pic_new = cast(pic_new,oldClass);
end
Updated: I was able to resize the image both along rows and columns. However, it doesn't work right
This is the original image: https://imagizer.imageshack.us/v2/895x383q90/r/903/4jM76I.png
This is the image after being enlarge 2.5 along rows and shrunk 1.3 along columns: https://imagizer.imageshack.us/v2/323x465q90/r/673/EHIaoB.png
Why is there such a black box in the result image?
Updated 2: This is how I did: in the command window type
>> img = imread('pic.pgm');
>> newImage = zoom_image(img, 2.5, 1/1.3);
>> imshow(newImage)

Answer 1

Using imresize it can be easily achieved
pic_new = imresize( pic, newSize, 'bicubic' );
Where newSize is the new size of the image (height and width). The new aspect ratio can be arbitrary and does not have to be the same as the aspect ratio of the new image.
For example, shrinking an image by 1/2 along the rows and leaving number of columns unchanged:
[nCol nRows] = size( pic(:,:,1) );
pic_new = imresize( pic, [nCols round( nRows/2 ) ], 'bicubic' );

Answer 2

Try editing your function to have a separate zoom for rows and columns, a la
function pic_new = zoomfunc(pic, zoom_valueX, zoom_valueY)
actualSize = size(pic);
newSize = max(floor([zoom_valueY zoom_valueX].*actualSize(1:2)),1);
newX = ((1:newSize(2))-0.5)./zoom_valueX+0.5; %# New image pixel X coordinates
newY = ((1:newSize(1))-0.5)./zoom_valueY+0.5;
oldClass = class(pic); %# Original image type
pic = double(pic); %# Convert image to double precision for interpolation
if numel(actualSize) == 2
pic_new = interp2(pic,newX,newY(:),'cubic');
end
pic_new = cast(pic_new,oldClass);
end