what is the map in this example?

when I try to run this code in MATLB, it doesn't work in which showing cant find the variable of map for colormap(map). does anyone know what the map is here?

[Dyuman Joshi]

The variable map is part of the file mri.mat -

%Check the file location
which mri.mat

/MATLAB/toolbox/matlab/demos/mri.mat

load mri.mat

%check the contents loaded into the workspace (ignore cmdout)
whos

  Name          Size                   Bytes  Class     Attributes

  D           128x128x1x27            442368  uint8               
  cmdout        1x33                      66  char                
  map          89x3                     2136  double              
  siz           1x3                       24  double              

A generally preferred is to load the data into a variable -

out = load('mri.mat')

out = struct with fields:
      D: [128×128×1×27 uint8]
    map: [89×3 double]
    siz: [128 128 27]

Answer 1

[Chunru]

"map" specifies the color of the image.

load mri

  Name          Size                   Bytes  Class     Attributes

  D           128x128x1x27            442368  uint8               
  cmdout        1x33                      66  char                
  map          89x3                     2136  double              
  siz           1x3                       24  double              

Answer 2

[DGM]

Ah. This is one of the hazards of using load() like this.

When you run the line

load mri

... you're loading the contents of mri.mat into memory. Three new variables magically appear in the workspace without ever being declared anywhere in the code.

One of the three is the variable called map. It is an 89x3 gray colormap. The map is almost perfectly linear and full-scale, so if you really wanted to, it would probably suffice to replace it with gray(89), but that shouldn't be necessary. Check to make sure you're loading mri.mat and that the contents are showing up in the workspace.