2_Coding_Presentation_Lesson_1_variant_1

10.3.1.1 present raster images in binary

1. Students watch the video and take notes of the important points.
2. After the video, each student in the class has to tell 1 fact from the video.
3. The fact should not be repeated twice.
After watching the video, students will understand that the lesson is about encoding bitmap graphics.

0 – White,
1 – Black

Bitmaps

Bitmaps are the name given to one way of storing graphics on a computer system.
A bitmap is laid out in a grid format with each box on the grid containing one “Picture element” which is better known as a “Pixel”.

Copy the Bitmap Images spreadsheet from the school network into your own work area and then open the file.

7

Look at the image in the grid on the left. You are going to fill in the grid on the right with either a 1 or a 0 in each box.
1 = part of the image is showing in the box
0 = the box is empty

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Once you have completed the grid then click on the next worksheet called “Final 8 x 8 image” and all the 1’s will be shown as black and the 0’s you entered will be shown as white.
What has happened to the quality of your image?

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It is not the same quality as the original image.
This is known as “Pixelated” where the image is made up of large blocks rather than smooth lines.
This can happen to small or poor quality images you copy from the internet when you try to make them larger.
How can we get a better quality image using this technique?
We can use a more detailed grid, we will do the same again but rather than an 8 by 8 grid, we will use a 16 by 16 grid.

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Move onto the next worksheet and repeat the process with a 16 x 16 grid.



Have a look at the final 16 bit image on the next worksheet.
What happened to the quality of the image compared with when we had an 8 x 8 grid?

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We have only been working on small grids but usually bitmaps have many more pixels to make up the picture and typically have thousands of pixels for one image.
A typical screen size is 1280by 800 pixels which works outas (1280 x 800) 1,024,000 pixels to cover the whole screen.

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The image you have just created uses 16 x 16 pixels and we are only allowing 1 bit or each pixel to show either 1 for black or 0 for white.
If we wanted to have colour in the image you would need more bits per pixel so that you can allocate a particular colour rather than just black and white.

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We are going to use a wider range of numbers to make a colour image. Use the numbers 0 to 3 inclusive. Make up your own image using these colours.

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With 1 bit per pixel you can have only 2 colours (black or white).
0 = White
1 = Black
With 2 bits per pixel you can have 4 colours.
00 = White
01 = Red
10 = Green
11 = Blue
Normally colour images have many more colours and so use more bits per pixel.

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How many colours can be saved with 3 bits per pixel?
-8
How many colours can be stored with 16 bits per pixel?
-65,536
Most images have 24 bit colour which allows over 16 million colours.

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N = 2i
N- number of colors displayed on the screen,
i – color depth.

In order to work out the image size you would need to know:
-The size of the grid (width and depth)
-The number of bits per pixel for the colour depth
For instance an image which is 1000 x 800 pixels with a 16 bit colour depth would be:
-(1000 x 800) x 16 = 12,800,000 bits
-This is more commonly written as 12MB.

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Challenge 1Modern monitor allows you to receive on the screen 2048 different colors. How many bits of memory takes 1 pixel?

One pixel encodes by using 0’s and 1’s.
N = 2i, N- number of colors displayed on the screen, i – color depth
Given that N=2048
Find i
2i =2048, i=11
i=log2 2048 =11 bit

Challenge 2

Calculate the required amount of video memory in graphics mode 1024 x 768 pixels and a color depth of 16 bits per pixel
Screen pixels’ size:
1024 • 768 = 786 432
required amount of video memory:
16 bit • 786432 = 12 582 912 bit =
=1 572 864 byte = 1 536 Kbyte = 1,5 Mbyte.

Let’s represent formula of calculation amount of video memory in graphical image: V=i*X*Y

Challenge 3

Calculate the required amount of video memory in graphics mode 800 x 600 pixels and a color depth of 24 bits per pixel.
Screen pixels’ size: 800 • 600 = 480 000. required amount of video memory:
24 bit • 480 000 = 11 520 000 bit = 1 440 000 byte =
= 1406,25 Kbyte = 1,37 Mbyte.

«Check yourself» through brainstorm “Linoit”
Linoit service can perform the role of online board, through which canvases with sheets of stickers are created. Teacher invites students to answer questions using stickers.

Task 1.  Each point of the monitor screen (pixel) is assigned four bits, which will display n colors.
Task 2. The video memory size is 4 MB, the bit depth is 24, the display resolution is 640 x 480. What is the maximum number of pages that can be used under these conditions?