why the grayscale image has 3 channels

Question

i am performing operations on a grayscale image, and the resultant image of these operations has the same extension as the input image. for an example if the input image is .jpg or .png the output image is either .jpg or .png respectively.

and I am converting the image into grayscale as follows:

ImgProc.cvtColor(mat, grayscale, ImgProc.COLOR_BGR2GRAY),

and I am checking the channels count using:

.channels()

the problem is when I wnat to know how many channels the image contain, despit it is a grayscale image, i always receive umber of channels = 3!!

kindly please let me know why that is happening

Solution

The depth (or better color depth) is the number of bits used to represent a color value. a color depth of 8 usually means 8-bits per channel (so you have 256 color values - or better: shades of grey- per channel - from 0 to 255) and 3 channels mean then one pixel value is composed of 3*8=24 bits.

However, this also depends on nomenclature. Usually you will say

"Color depth is 8-bits per channel"

but you also could say

"The color depth of the image is 32-bits"

and then mean 8 bits per RGBA channel or

"The image has a color depth of 24-bits"

and mean 8-bits per R,G and B channels.