Pixels

• Computing
• Lower Secondary (Key Stage 3)

Pixels

By the end of this lesson you will know how binary is used to represent digital information.

Why do humans use denary instead of binary?

How many bits are in a byte?

1. 1
2. 2
3. 4
4. 8

how many kilobytes are in a megabyte?

1. 1
2. 100
3. 1000
4. 10000

How is this made?

Images are made up of bits of data called pixels. Pixels are the smallest unit of a digital image. Each pixel is a small square that contains a colour.

The combination of pixels creates the whole image.

What are images made up from?

The number of pixels is called the resolution. The resolution of an image is calculated the same way as the area of a square:

width * height

12 * 19 = 

resolution of 

The TikTok logo on a mobile device has a resolution of 1080*1920 which is 2 million pixels or 2 megapixels. a mega pixel is 1 million pixels.

Higher resolution images are great because they have increased image quality, but that comes at a cost to file size. this means the higher the resolution the better the image but it costs more storage, has a higher processing time and loading time.

How do we calculate the resolution of an image?

Every pixel as it is a computer image is made of binary digits. remember binary is not about numbers it's how computers represent everything. The fixed number of binary bits used to represent a pixel is called colour depth. 

Instructions:

Step 1

Recreate the picture on Piskel (the link is on the next page, the image on the page after), change the image size to 11x12 YOU WILL NEED TO UNTICK THE MINTAIN ASPECT RATIO box.

www.piskelapp.com

0 = white

1 = black

2 colours make up this image, for two colours we need a colour depth of 1. This is because we can use 0 - white and 1- dark blue. We assign the binary values to colours when making our own art, in a computer these values are pre-assigned.

00 = white

01 = yellow

10 = blue

11 = red

Look at this image, how many colours does it have? and how would we represent this?

What is the colour depth of the image?

2 binary bits, so a  color depth of 2

00	white
01	yellow
10	blue
11	red

Note: if you are using 2 bits you cannot use 1 bit, all bits must be the same not a mix of 1,2 or even 3 bits.

Instructions:

Step 1

Create a picture a new picture on Piskel that you want to make, You can draw anything appropriate, each pixel must have  colour in it and you can only use 4 colours. 

Step 2

Use one or two binary digits to represent the colour of each element. You will then write out the binary eg 00 for white, 01 for red as was done in the emoji and Mario example 

You can:

Decide which binary digit (or pair of binary digits) corresponds to which colour

You cannot:

Use one binary digit for some colours and two for others — you must use either one or two binary digits for all colours.

Step 3

Draw a binary bitmap out for the image you have created again as shown in the example.

What are the individual elements in the image called?

There are 448 individual elements in a image. What is this number called?

What is the colour depth of a four colour image?

What do the 2 binary digits, stored for each element, represent?

How many bits are needed to represent this image?

How do painters make orange?

In practice, colour is commonly represented using 24 bits. Purple is rgb(240,53,230)

Red - 11110000

Green - 00110101

Blue - 11100110
 

Representation size:

How many bits are required to represent an image?

Resolution x Colour depth!!!

If a picture is 10 pixels x 10 pixels and has red, blue, yellow and green in it. How many bits are needed to represent the image

1. 100
2. 200
3. 104
4. 400

Carry on the completing the worksheet you were given and here is the link for the RGB calculator.

               Click here               

One thing I learned this lesson was

one thing I dislike about this lesson was?

Overall I feel I learned a little/ a lot this lesson

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