How do I convert a 4D image to a scalar one?

I have a 4D stack of images and need to convert it to scalar so I can multiply every each individual slice with a vector. Any idea?

[Rik]

A scalar in matlab is a single value. So converting your array to a scalar is probably not what you want.

[Stelios Fanourakis]

So how do I do it? How can I multiply every slice of that 4D stack to a specific vector (translation matrix) of mine?

[Image Analyst]

What does that mean, to multiply a slice "to a vector"? I have no idea. Do you have a translation matrix for every slice of a stack of color images? So each color image gets moved by a different amount and direction? Or do you just want to multiply the value by a scalar? For that matter, what does "slice" mean in a 4-D context? A "slice" of a 4-D matrix is a 3-D matrix, which could be a color image. Or it could be a volumetric or some other interpretation of a 3-D "slice" of the 4-D matrix. For any dimension, a slice is usually thought of as being one less dimension than the original. A slice of a 3D image is a 2D image. A slice of a 4-D image is a 3-D image. A slice of a 15 dimension matrix is a 14 dimension array. Etc.

[Stelios Fanourakis]

Slices of 15 images result to a 4D stack of images im(:,:,:,:). I need to translate every one of those 15 slices to different positions that derive from a translation matrix. How do I do that?

Answer 1

[Image Analyst]

Try this:

imSize = size(im);
for k = 1 : imSize(4)
    % Extract one 3-D image from the 4-D image.
    thisImage3D = im(:, :, :, k);
    % Now determine translation parameters somehow
    translationParameters = GetTransform(thisImage3D);  % You write this...
    % Now apply those paramters to this 3-D image we extracted.
    % Again you write this function.
    transformedImage3D = ApplyTransform(thisImage3D, translationParameters);
    % Stick it back in im
    im(:,:,:,k) = transformedImage3D;
end

Don't ask me how to "derive from a translation matrix" because I have no idea how you plan on getting that matrix. Presumably you know how to do that already.

[Stelios Fanourakis]

It is not working for every image. I get a fixed standard translation for the whole image stack without changing. See my answer to the other post.

[Stelios Fanourakis]

Can't someone help me on this???

[Stelios Fanourakis]

I have another assumption. im2 is a 4D interpolated stack of images (stack out of 15 images) using interp3.

Interpolation to me, means that it creates in between images. For example, if there is 1 to 2 image, the interpolation will give us 1.5 image. Am I correct? So that's what interp3 does. It increases the number of images above 15, where they really are.

Then, by importing im2 to GriddedInterpolant, again another interpolation takes place, so even more subimages are created. Thus, the total number of slices that consist the stack may exceed 30, but, definitely it won't be 15 where it started.

Then, with GridVectors I turn it to cell array and by multiplying with the translation_vector, supposedly they are shifted. BUT, the translation_vector matrix is consisted out of 15 rows and 2 columns. 15 rows as the original images NOT the interpolated ones. So, a lot of images do not shift.

Am I right to my assumption. Is this more clear so we can find a solution?

[Stelios Fanourakis]

@Matt. I though of another solution. When I use result = F(g) I apply interpolation again to g which are the original set points (image) multiplied by translation_vector.

That means that the original image has already been shifted plus a new interpolation coming on the way (F(g)). Does it make it somehow to be smushed or squeezed?

If I visualize with only g without F(g) I get errors later on to the uicontrol of the slider (e.g. Index Exceeds Matrix Dimensions).

Would it be correct to visualize only with g?