Error while using rgb2gray

I m trying to accept series of color images and apply edge function on them. this is my code....

if true
for k = 1:10
   tifFilename = strcat( num2str(k), '.tif');
   [X,map] = imread(tifFilename);
   gmap = rgb2gray(map);
   BW = edge(gmap,'sobel');
   figure, imshow(BW);
end
end

it shows the following error

??? Error using ==> rgb2gray>parse_inputs at 82 MAP must be a m x 3 array.

Error in ==> rgb2gray at 35 X = parse_inputs(varargin{:});

Error in ==> sequenceimageprocessing at 6 gmap = rgb2gray(map);

Answer 1

[Image Analyst]

Color images don't have a colormap. Try this

fontSize = 20;
for k = 1:10
   tifFilename = sprintf('%d.tif', k);
   if ~exist(tifFilename, 'file')
      fprintf('%s not found.\n', tifFilename);
      continue;
   end
   rgbImage = imread(tifFilename);
   grayImage = rgb2gray(rgbImage );
   BW = edge(grayImage ,'sobel');
   subplot(2,2,1);
   imshow(rgbImage);
   title('Color Image', 'FontSize', fontSize);
   subplot(2,2,2);
   imshow(grayImage );
   title('Grayscale Image', 'FontSize', fontSize);
   subplot(2,2,3);
   imshow(BW);
   title('Binary Edge Image', 'FontSize', fontSize);
end

Answer 2

[Azzi Abdelmalek]

Maybe your image is not RGB, check

size(X)

[Febin Benjamin]

size is= 480 640

nw what should i do?

[Azzi Abdelmalek]

In windows Matlab command, just to check if your image is nxmx3

[Febin Benjamin]

i did that.... and it showed me this....

ans=
480 640

now what should i do?

[Azzi Abdelmalek]

Nothing, your image is already grayscale

[Febin Benjamin]

And what if it shows

ans =
        3058        3382           3

m sorry if m irritating u..... m a rookie actually.... :)

[Azzi Abdelmalek]

Have you the same error message with this case?

[Azzi Abdelmalek]

[X,map] = imread(tifFilename)

Check if map is nx3 array

then write

gmap = rgb2gray(map);