I have a problem understanding colormaps in Matlab and using them to import and diplay .gif images.
I would like to import an image using
im = imread('I.gif')
and then display it using
imshow(im)
but the result is wrong
If I do
[im,map] = imread('I.gif')
and then display it using
imshow(im,map)
it works properly, but still I don't understand the need of this colormap
Is there a way to import and convert my gif image to greyscale so that when I do
imshow(im)
it shows the correct greyscale image without having to worry about the colormap?
SOrry for the noob question but I am just starting with image processing in Matlab and I would really appreciate some help. It is my first question! :)
Bye and thanks!
If you want to convert your gif to grayscale, use ind2gray:
[im,map] = imread('I.gif');
imGray = ind2gray(im,map);
The reason that you need the colormap is that the gif format doesn't store image intensities, it stores indices into the colormap. So color 0 could be red or green or a very light shade of mauve. It's the colormap that stores the actual RGB colors that the image needs. ind2gray will take each of those colors, convert them to a grayscale intensity, and replace the indices in the image with those intensities.
It looks like you've really already answered the question. It seems that .gif files support an indexed color format, as a way of saving space. See:
https://en.wikipedia.org/wiki/Indexed_color
This is different than a more typical RGB color, which is what is often received from an IMREAD call.
To convert to a grayscale, you would need to go through the colormap and assign a grayscale value to each color, and then substitute those values back into the im variable.
