how to use imshow for this array?
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hello, I have attach my image. I want to use imshow. However, it shows as white and nothing appears when I use imshow. I want to see a coloured image. This array is the output of a pixel-based classification. Please advise.
EDIT: I added output example pic that I am looking to get. It will not be the same exact pic but should have the same color scheme and look similar.
thanks Aud
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It's not imshow but you could use imagesc instead
imagesc(out_map)
If you really want to use imshow, then
B = mat2gray(out_map)
imshow(B)
in which case you have to apply a colormap, because your matrix is not an RGB image.
7 个评论
madhan ravi
2018-10-25
+1 learning a lot about image processing from you :)
audley james
2018-10-25
@madhan, thanks :)
@audlay,
To change colormap
colormap(jet(10))
'jet' is the name of a colormap and the number is the number of segments.
The image youve uploaded appear to be segmented by something other than color?
audley james
2018-10-25
编辑：audley james
2018-10-25
You don't have to apply a colour map or use mat2gray to see the image with imshow if all you want to see the raw grayscale image:
imshow(out_map, [])
The [] tells imshow to map the minimum and maximum intensity in the image to black and white respectively, instead of using the default range of [0 1] = [black white]
You can of course apply a colour map after that:
colormap(parula)
With regards to colour maps, I would avoid jet or similar rainbow maps. A search for 'rainbow color map harmful' in your favorite search engine will find lots of sites explaining why including this paper by Mathworks
Adam
2018-10-25
You can also create your own colourmap with defined colours or just random as
cmap = rand( 10, 3 )
if you have 10 classes and provided the caxis scaling is appropriate to map 1 per class.
Obviously if choosing your own 10 colours you would just put them into a 10 by 3 array like the one randomly created, e.g.
cmap = [1 0 0; 0 1 0; 0 0 1; 1 0 1;...];
where you put all your colours in instead of the ... of course.
I agree with guilliame that 'jet' is a poor colormap for visualizing intensity and completely useless if you print in grayscale. If the purpose is to show a number of distinct regions in different colors, then it is quite OK because it covers a wide range of colors (still useless in grayscale though).
Just set the number of segments to the number of unique values and pick another colormap. Personally I like the magma and inferno colormaps but they are not part of the default ones.
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