P2 T1 L10 - Representing images

Question 1

(Binary recap)

For n number of bits there 2^n possible combinations

How many combinations can be represented by: (just give 2^n)
8 bits
16 bits
24 bits

Answer 1

8 bits = 2^8 = 256
16 bits = 2^16 = 65536
24 bits = 2^24 = 16777216

Question 2

(Computer data)

A computer often has to store and process real-world data.

A computer needs data in a format it can understand: patterns of _s and _s.

This type of data is referred to as ______ _____.

It is different from _________ _____ which can in theory be measured to any degree of accuracy.

Answer 2

1 0

digital data

analogue data

Question 3

(Seeing images)

Humans see ‘images’ by detecting the light reflected by objects they are looking at.

Light is transmitted as ______ and changing ____ lengths produce different colours.

Even though a human cannot detect them all, there is an infinite number of possible colours.

When a photo is taken using a digital camera, the embedded computer needs to _______ and ___________ these colours.

Answer 3

waves

wave

capture

approximate

Question 4

(What is a pixel)

Define pixel (2 points)

Answer 4

1. A pixel is the smallest unit of a digital image or graphic that can be ADDRESSED, DISPLAYED and REPRESENTED on a digital display device.
2. It is a number value that REPRESENTS A COLOUR

Question 5

(Capturing an image)

When a digital camera captures the image it breaks up what it sees through its lens into a _____ __ _____.

A light sensor measures the _________ ___ ________ in each pixel.

Each measurement is converted into a binary code using an
electronic component called an __________-__-_________ __________.

The number of pixels recorded in the grid affects the number of bits used and, therefore, the ____ of the file created.

Answer 5

grid of pixels

intensity of colour

analogue-to-digital convertor

size

Question 6

(Bitmapped Raster Graphics)

Bitmapped graphics are created using a grid of _____.

Each pixel is given a _______ _____.

Answer 6

pixels

colour value

Question 7

(Types of bitmap files)

An image that is compromised of pixels is a _______ ____.
Common types of this are: (name 5)

Answer 7

1. BMP
2. JPG
3. GIF
4. PNG
5. TIF

Question 8

(Bitmap resolution)

The number of pixels used to make up a bitmap image is defined by the _________.

The area is defined by the image _____ and ______ in pixels e.g. 1080x768

72dpi = screen resolution
300 dpi = print quality resolution

Answer 8

resolution

width height

Question 9

(Number of pixels)

Resolution is defined as _____ x ______

A typical bitmap might be 1000 x 1000

This would mean a total of 1,000,000 pixels would be used.

Typically this would be referred to as a 1 _________ ______.

Answer 9

width height

megapixel image

Question 10

(Image size)

Resolution doesn’t define the actual physical size of an image.

If an image is made bigger (or smaller), the size of each pixel grows or shrinks to maintain the required _________.

This is why there is a __________ in quality when a bitmap is resized.

Answer 10

resolution

deterioration

Question 11

(Creating an image)

Each Pixel is given a _______ _____.

Each ______ represents a different colour

Using one bit per pixel allows only 2 values, 0 and 1

More bits per pixel = more colour combinations

Answer 11

binary value

value

Question 12

Each pixel can represent a finite number of colours.

A pixel is attributed a number of n bits.

The number of combinations (2^n) dictates the ___ _____ and therefore the number of colours that can be represented.

A ______ bit depth gives a greater range of colour and a better quality of image.

8 bits per pixel = 28 = 256 colours
16 bits per pixel = 216 = 65,536 colours
24 bits per pixel = 224 = 16,777,216 colours

Answer 12

bit depth

higher

Question 13

(Variation in quality)

Changing the colour depth of an image will affect the number of _______ it can display.

Answer 13

colours

Question 14

(Colour codes)

Colour values of individual pixels are expressed as denary ____ values and in ___________.

RGB (Red, Green and Blue) values range between 0 - ____

Answer 14

RGB

hexadecimal

255

Question 15

(Calculating file size)

Image file size is determined by the number of _____ used and the number of _______ ____________ available.

Quality is traded off against file size – you can’t have high quality and a low file size

Answer 15

pixels

colour combinations

For example:

• An image is captured on a 2 megapixel camera
• Image captured with a 24 bit colour depth
• 2,000,000 x 24 = 48,000,000 bits / 8 = 6,000,000 bytes or 6 MB

Question 16

Metadata is _____ _____ _____ and is stored in the same file as the image data

Give 4 examples of metadata.

Answer 16

data about data

This includes:

1. the date it was created
2. the width and height in pixels of the image
3. the colour depth and
4. the GPS coordinates of where a photo was taken

Question 17

(Plenary)

Resolution is the density of ______ over an area, it is not the physical size of the image.

Colour or bit depth determines the number of colours that an image can ______.

Image quality comes at the expense of ____ ____.

Metadata is stored with ______ and specifies the width, height and colour depth amongst other details.

Answer 17

pixels

display

file size

images