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Difference between Monochrome, Grayscale and black and white images

There are many of us who must have heard words like Monochrome, Black & White, Grayscale and 32-bit colour images. These words carry more meaning when you have to deal with images being a DSLR lover or photographer. I was trying to scan an image recently and noticed a difference in the quality when selected grayscale instead of black & white. Also, what would be the difference between monochrome and black and white? Both of these thoughts served as the source of motivation for this post. Let's dive in and see what's the difference in all these terminologies. 
Monochrome photos: Monochrome image is known as a binary image. Each pixel is stored as a single bit (0 or 1). A 640 x 480 monochrome image requires 37.5 KB of storage. It can also contain varying tones of only one colour. 

Black & White photos:
It has no Gray. It can also be considered as a special case of monochrome images. A good example of black & white would be a chess board. All black & white printings are monochrome but not all monochrome printings are black and white. 

                                                                        Grayscale image 

Grayscale photos:
A grayscale image has values varying from black to white. In other words, it has varying shades of gray. In simple words, a grayscale image has more details than a black&white image. A 640 x 480 sized grayscale image would require over 300 KB of storage. 

Colour images or photos: Can be either 8 bit, 24 bit or 32 bit. 
8 bit: One byte for each pixel. Supports only 256 out of the millions colour possible. (Calculated as 2^8)
24 bit: Each pixel is represented by 3 bytes as 1 byte=8 bit. These bytes are known as red, blue and green. 24-bit colour images offer the largest possible colour combinations. 256x256x256. (Calculated as 2^8 multiplied by 2^8 multiplied by 2^8).
32 bit: These images have 8 additional bits for alpha (transparency). 
Tip for photoshop: Any RGB image that has 8 bits/channel is known as a 24-bit image. 8 Bit for each red, blue and green colour. Photoshop lists the bit depth as bits/channel. Sometimes organizations will ask for a 24 bit JPEG which means 24 bits in total or 8 bits/channel in the language of photoshop. 

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