Crossing the boundary - analogue universe, digital worlds
Crossing the boundary - analogue universe, digital worlds

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Crossing the boundary - analogue universe, digital worlds

4.6 Greyscale

If this seems inadequate – it does seem rather an impoverished range of shades – all we need to do is allocate more bits. Three bits per pixel will give us eight shades, from black to white; four bits per pixel gives us 16 shades; and so on. This mapping of shades of grey between black and white in a black and white bitmap is known as greyscale. The range of numbers to which a pixel can be mapped is termed the pixel amplitude.

Let's try a simple example. I'm going to take the first of the two images in Figure 17. Once again, I can lay a grid over the image as in Figure 18, which I've enlarged a bit, to demarcate the pixels. Note that I'm only working with a section of the picture, near the nose of the aircraft.

Figure 18
Figure 18 Picture of aircraft divided into pixels

Now I need to inspect each pixel and decide on the closest shade of grey to represent what appears in the square. For simplicity, I've decided to use six shades of grey, as well as black and white. The result is shown in Figure 19. It's not brilliant, but that can be put down to a fairly large pixel size and a limited choice of greys.

Figure 19
Figure 19 A greyscale image of the aircraft

Finally, I can map each pixel in the image onto one of the eight binary numbers between 000 and 111 inclusive, depending on whether the image at that pixel is black (111), white (000) or some shade of grey between. The mapping in the small area I've marked will look like this:

The sequence of binary numbers to represent this picture
The sequence of binary numbers

which is tedious enough to demonstrate just how simplistic the interior world of the computer is.

M150_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371