# Grayscale, monochrome, binary image in matlab

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MKN on 14 Feb 2015
Commented: Image Analyst on 11 Mar 2015
In Matlab,
1. An 8-bit gray scale image has pixel values ranging from 0 to 255. The pixel depth may vary (16-bit, 32-bit, etc)
2. A binary image has pixel values, either 0 or 1 (logical) My question is that, is monochrome image, a binary image or a gray scale image as per points 1 and 2. I need clarification because I want to be 100 % sure about monochrome image.
(As per 'Digital Image Processing Using Matlab' by Gonzalez, Woods, Eddins, a monochrome image is a grayscale image. (Topic 3.2, pg no. 66))
Comments, suggestions are welcome.
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Geoff Hayes on 14 Feb 2015
MKN - I would (rightly or wrongly!) define a monochrome image as one that consists of various shades of a single colour. So you could fix the red and green channels, and then vary the blue from 0 to 255 (or whatever the pixel depth is: 8, 16, 32, etc.). For gray scale, the red, green and blue channels would be identical.
Using the above, a gray scale image would be considered a monochrome image, but a monochrome image would not necessarily be a gray scale image.
A binary image has two colours, typically black (0) and white (1). Though if 8 (or more) bits are used for the two colours and/or three channels, then you could have two other colours (of your choice) used to represent the binary image.

Guillaume on 14 Feb 2015
A monochrome image is an image with only one colour channel. Thus, both greyscale and binary images are monochrome. Note that the pixel intensities don't necessarily have to be represented in grey, you could just as well use different shades of red.
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Image Analyst on 11 Mar 2015
Sounds right to me. Not sure why MKN isn't accepting this answer.