3.4 Extending skills
Answer
The first is that smaller file sizes need less storage space. The second is that information can be transferred much more quickly because of the smaller amounts of data needed.
25 Part 4
So, to sum up, in this lecture, we’ve looked at how sound and image information is transformed into digital data and then back into information again and what factors will affect the quality of the image that we see or the sound we hear. Compression is the process by which we can reduce
file or signal size and it has two main benefits. The first is that smaller file sizes need less storage space. The second is that information can be transferred much more quickly because of the smaller amounts of data needed. A key point from this lecture is that the quality of
information in image and audio is very dependent on how the information is transformed into data in the first place. For example, a high-quality sensor can capture large numbers of pixels to represent the image that we want to store. Depending on the data standard that we choose to encode the file, either all of the data representing the image can be stored, or we can use compression techniques to reduce the file size, making it easier to work with. However, if we have a low-quality sensor, then we can only capture a much smaller number of pixels, and using compression techniques will not make a lot of difference to the quality of the image that we see on a screen or in print. The same is true of audio data. If the digital sampling
rate we have used is very low, for example, let’s say we have recorded some music at 8 kHz – suitable for voice only, rather than 44 kHz – suitable for music, then the data compression techniques we use will have little effect on the quality. Data compression techniques are an essential tool in
balancing quality and file size. However, they are only one part of the process in transforming information to data and then back again to something we can see or hear. It is important to consider all the different parts of the process … You will notice that I haven’t discussed video standards in the lecture today and that is because we will look at these in a separate lecture, where we will also look at compression in more detail.
E
SKILLS BANK 3.2 Asking for information
Remind students that it is important to know how to ask for additional information, both from their classmates and from their lecturers. They have already covered the phrases for asking for information from other students.
This activity will help them to revise phrases for asking for information from a lecturer, as in Skills Bank 3.2.
26
Set for individual work and pairwork checking. Play the recording, and feed back verbally.
Answers 1. Could you go over the bit about pixels again? 2. I wonder if you could repeat what sampling is again?
3. I didn’t quite understand what you said about the difference between a bitmap and a vector.
4. Would you mind giving the information about colour depth again?
26
1. Could you go over the bit about pixels again? 2. I wonder if you could repeat what sampling is again? 3.
I didn’t quite understand what you said about the difference between a bitmap and a vector.
4. Would you mind giving the information about colour depth again?
F Set for pairwork and general feedback.
If students are finding it difficult to come up with ideas, suggest that they consider some of the predictions they made about the lecture at the beginning of the lesson. Are there any questions which have not been answered?
Some possible ideas are given below.
Possible answers • When were the different types of compression discussed in the talk introduced?
• What new types of compression have been developed recently?
• Have new types of hardware made compression more important (e.g., 4k video)?
G
Explain to students that this activity will help them to revise some of the definitions they heard in the lecture. 3.4_G
Set for individual work and pairwork checking. You could give students the blank table provided in the PDF.
Feed back visually to the group (the completed table is also included in the PDF).
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