Unit 1; DIGITAL IMAGES

Question 1

What is a bitmap image made up of

Answer 1

Pixels!

Question 2

Where does the word “pixels” come from?

Answer 2

PICture ELement

Question 3

What is a pixel

Answer 3

• A pixel is the smallest identifiable area of an image.
• Each pixel is a single color, and is given a binary value which represents the color
• A pixel’s color can be changed by changing it’s value
• Each value represents a different color

Question 4

What is image resolution?

Answer 4

Resolution is the concentration of pixels within a certain area.
E.g. if there are four pixels in the image, the image resolution is 2 x 2.

• The area is defined by the image width and height in pixels. E.g. 3241 x 4323

Question 5

How do the number of bits per pixel impact anything?

Answer 5

If there was only 1 bit per pixel, there could be only two colors (with values 1 and 0)

More bits per pixel = More color combinations

1 bit per pixel = 2 possible colors
2 bits = 4 colors
3 bits = 8 colors (because 2^3 = 8)
4 bits = 16 colors

Question 6

Calculating how many bits per pixel there are

Answer 6

If there are 256 colors, then you have to do 2 to the power of what equals 256? (because binary is in base 2)

Well, 2 ^ 8 = 256, therefore there are 8 bits per pixel.

• The number of bits per pixel there are is called the color depth

Question 7

Calculating file size in bits.

Answer 7

You do the image resolution multiplied by the number of bits per pixel.

I.e. if the image resolution was 20 x 20, and there were 3 bits per pixel, then 20 x 20 x 3 = 1,200, and 1,200 is the file size.

Question 8

Calculating file size in bytes.

Answer 8

If the file size in bits is 1,200, then divide that by 8, the file size in bytes is 150.

• Another example, is the file size in bits is 300, then divide that by 8, which equals 37.5, we can’t have a decimal though, so the file size in bytes would be 38.

Question 9

What is RGB?

Answer 9

Red, Green, Blue.

• Values range between 0-255, this means in the 256 possible color values, there are 8 bits per pixel

Question 10

What is Metadata?

Answer 10

• Metadata is data about data

Some examples include:
- The color depth in bits per pixel
- The resolution (width and height in pixels)
- The date and time a picture was taken
- The author/photographer of a picture

Question 11

What is lossy compression?

Answer 11

JPG

• Reduces file sizes
• Removes data permanently
• Tries to reconstruct an image without missing data
• Much smaller files sizes but some loss of quality (e.g. can go from 380KB to 21KB)

Question 12

What is lossless compression?

Answer 12

PNG

• Finds areas with the same color and records them as 15 blue pixels rather than blue pixel, blue pixel, blue pixel, etc.
• 10, 10, 10, 10, becomes 01 - 10

Question 13

Image file types

Answer 13

• PNG
• JPG
• BMP
• GIF