Question

The following code produces the error:

Warning: Dimensions of AlphaData must be 1×1, or must match CData.

The problem is that CData is a color image and thus has 3 dimensions, and alphadata is a matrix of transparancy data abd thus has 2 dimensions.

red = cat(3, ones(512), zeros(512), zeros(512));
mask = [];
bounds = data(currow,1:6);
if slice >= bounds(5) && slice <= bounds(6)
    mask = zeros(size(segmask,1),size(segmask,2));
    mask(bounds(1)-4:bounds(2)+4,bounds(4)+4:bounds(4)+5) = 1;
    mask(bounds(2)+4:bounds(2)+5,bounds(3)-4:bounds(4)+4) = 1;
end
imshow(low(:,:,slice),[WL-WW/2 WL+WW/2])
hold on
h = imshow(red);
set(h, 'AlphaData', 0.3*mask);
hold off

Here is the info on AlphaData and CData from the Matlab Documentation

---

AlphaData m-by-n matrix of double or uint8

Transparency data. A matrix of non-NaN values specifying the
transparency of each face or vertex of the object. The AlphaData can
be of class double or uint8.

MATLAB software determines the transparency in one of the following
ways:

Using the elements of AlphaData as transparency values
(AlphaDataMapping set to none)

Using the elements of AlphaData as indices into the current alphamap
(AlphaDataMapping set to direct)

Scaling the elements of AlphaData to range between the minimum and
maximum values of the axes ALim property (AlphaDataMapping set to
scaled, the default)

---

CData
matrix | m-by-n-by-3 array

The image data. A matrix or 3-D array of values specifying the color
of each rectangular area defining the image. image(C) assigns the
values of C to CData. MATLAB determines the coloring of the image in
one of three ways:

Using the elements of CData as indices into the current colormap (the
default) (CDataMapping set to direct)

Scaling the elements of CData to range between the values
min(get(gca,’CLim’)) and max(get(gca,’CLim’)) (CDataMapping set to
scaled)

Interpreting the elements of CData directly as RGB values (true color
specification)

Note that the behavior of NaNs in image CData is not defined. See the
image AlphaData property for information on using transparency with
images.

---

How Can AlphaData and CData possibly have the smae dimensions?

In case red is 512x512x3 and mask is 512×512 and besides the warning the code seems to function as expected.

Answer 1

I figured out my problem. Because of the If statement the variable mask wasnt allays being created.