cmunique
Eliminate duplicate colors in colormap; convert grayscale or truecolor image to indexed image
Syntax
[Y,newmap] = cmunique(X,map)
[Y,newmap] = cmunique(RGB)
[Y,newmap] = cmunique(I)
Description
[Y,newmap] = cmunique(X,map) returns
the indexed image Y and associated colormap, newmap,
that produce the same image as (X,map) but with
the smallest possible colormap. The cmunique function
removes duplicate rows from the colormap and adjusts the indices in
the image matrix accordingly.
[Y,newmap] = cmunique(RGB) converts
the truecolor image RGB to the indexed image Y and
its associated colormap, newmap. The return value newmap is
the smallest possible colormap for the image, containing one entry
for each unique color in RGB.
Note:
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[Y,newmap] = cmunique(I) converts
the grayscale image I to an indexed image Y and
its associated colormap, newmap. The return value, newmap,
is the smallest possible colormap for the image, containing one entry
for each unique intensity level in I.
Class Support
The input image can be of class uint8, uint16,
or double. The class of the output image Y is uint8 if
the length of newmap is less than or equal to 256.
If the length of newmap is greater than 256, Y is
of class double.
Examples
Eliminate Duplicate Entries in Colormap
Use the magic function to define X as a 4-by-4 array that uses every value in the range between 1 and 16.
X = magic(4);
Use the gray function to create an eight-entry colormap. Then, concatenate the two eight-entry colormaps to create a colormap with 16 entries, map. In map, entries 9 through 16 are duplicates of entries 1 through 8.
map = [gray(8); gray(8)]; size(map)
ans =
16 3
Use cmunique to eliminate duplicate entries in the colormap.
[Y, newmap] = cmunique(X, map); size(newmap)
ans =
8 3
cmunique adjusts the values in the original image X so that Y and newmap produce the same image as X and map.
figure image(X) colormap(map) title('X and map') figure image(Y) colormap(newmap) title('Y and newmap')
