Grayscale image and imshow

2011 6 7
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I have a grayscale jpg image. I have used a window function to bring the edges down to 0 however over the range that i have multiplied (coulombs and rows on the outer edges of the image) by the window function there is a light blue tint in the picture ???
imshow should only display in black and white should it not??

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Walter Roberson
Walter Roberson 2011-6-7

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If you have a "grayscale jpg image" then that could mean that you started with an RGB image in which the R, G, and B channels were all equal. Manipulating such an image could potentially end up with unequal channels.
The alternative is that you had an indexed (pseudocolor) image whose colormap consisted entirely of gray entries; if so then the color the image would show up would depend upon the colors available in the colormap you are using.
Please check the size() of the image: it would have 3 dimensions if it is a truecolor image whose R, G, and B were all equal.

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Walter Roberson
Walter Roberson 2011-6-7
Oh yes, you might also want to command
colorbar
to have it put up a diagram of the current color scheme.
Brenden
Brenden 2011-6-8
Ok this makes sense but I am still getting to know matlab and not sure how to fix this. The image size is 2048x2048x3 unit8
Brenden
Brenden 2011-6-8
So as you said above if there are 3 dimensions then it is a colour image that is only in use of black and white pigment however if i tamper with the image i can get other colours...
So then how do i alter the original image to make it gray scale and therefore any mathematical operations i do wont give unwanted colouring?
Brenden
Brenden 2011-6-8
ok i tried to import the image a double but this does nothing. you have to use the command rgb2gray when importing the image...
ex: img=rgb2gray(imread('test.jpg')
thank you for your help Walter
BN

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