Matlab: Warning Dimensions of AlphaData must match CData

Question

The following code produces the error:

Warning: Dimensions of AlphaData must be 1x1, 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

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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)

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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.

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How Can AlphaData and CData possibly have the smae dimensions?

In case red is 512x512x3 and mask is 512x512 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.