What is a digital image?

As we know
Image may be defined as 2-dimensional intensity function f(x,y) where x,y are the spatial coordinates.
     But let us discuss apart from book. A 2-D image is nothing but a 2-D matrix. I think we all are familiar with the word Matrix. In matrix, each intersection of row and column is nothing but Cell. But where as in images we can simply say it as Pixel, that is what we discussed before.

     For any matrix it bears a number at-least '0' (ofcourse zero makes a vast difference during the processing of the images), which we called it as Value. But in images it is called it as Intensity values. 
     You are well familiar with Intensity value. Now i want to show you a diagram to explain about the brightness of the pixels in the image for each intensity values.

Changes in the colors at different grey percentages

     From the above chart we can simply recognize the change in the color, which is inversely proportional to the percentage of gray levels. (i.e, as percentage of gray level increases the brightness of a pixel decreases.)

NOTE:    It is important to remember that the intensity value for the color black is '0'(zero) and for white is '1' (as you expected) for an grayscale image.

     Finally, we can conclude that a Digital Image is nothing but a 2-D matrix with pixels having their intensity values, which are grounds for the deviation of the brightness in the image.

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