Presentation: File Formats and Quality

Slide 1 of 7 · Settling starter · Art · Year 8

5 minutes

File Formats and Quality

The same picture can be saved in lots of formats, and the format changes the file size, the sharpness and what you can do with it. Today you choose the right format for 5 real Eco Club jobs.

While the register is called: write your name, class and date on your worksheet, then read the stimulus sheet One image, exported five ways, including the five words at the bottom.

Starter question: The Pen y Fan photograph is 1.87 MB as a PNG. How big is the same photo as a JPEG at quality 80, and as a WebP?

DCF: Interacting and collaborating → Storing and sharing Parts A to C need no computers · work on your sheet

Slide 2 of 7 · Today’s brief and key words · Art · Year 8

3 minutes

Your brief: build a fact table, then pick the format for the job

You will fill in a fact table for JPEG, PNG, GIF, SVG and WebP, choose a format for 5 jobs, and prove each choice with a number from the stimulus sheet.

Lossy

The format throws away detail to get small, and you cannot get it back. Saving again loses a bit more each time.

Lossless

The format packs the data more cleverly but keeps every pixel. Re-saving costs nothing.

Vector

A list of shapes and coordinates the computer draws fresh every time. Enlarge it and it stays sharp. A bitmap is a grid of pixels and goes blurry.

Five words you need: bottom of the stimulus sheet Transparency (alpha) = see-through areas

Slide 3 of 7 · Part A: the format fact table · Art · Year 8

11 minutes

Part A: complete the fact table for the 5 formats

Write Yes or No, never a dash. Careful: one format can be saved lossy or lossless, and one has no pixels at all.

Format	Lossy or lossless?	Bitmap or vector?	See-through?	Animation?	Best at
JPEG	Lossy. Detail is thrown away and cannot be got back.	Bitmap	No, see-through areas come out solid white.	No	Photographs for websites and email: 212 KB instead of 1.87 MB.

Part A on your worksheet · 11 minutes Use the three export tables on the stimulus sheet

Supply teacher script (no subject knowledge needed)

Say aloud: “11 minutes for Part A. The board shows the JPEG row filled in. Do the other four rows the same way, using the three tables on the stimulus sheet as your evidence. Yes or No in every box, never a dash.”

Quick check answers: PNG: lossless, bitmap, see-through Yes (soft edges), animation No (the badge came out frozen). GIF: lossless but only 256 colours per frame (the sky went stripy), bitmap, see-through Yes but on or off so edges look jagged, animation Yes. SVG: lossless (text describing shapes), vector with no pixels at all, see-through Yes, animation Yes, best for logos at any size, 3 KB. WebP: either lossy or lossless, bitmap, see-through Yes, animation Yes, 138 KB against JPEG’s 212 KB.

Slide 4 of 7 · Part B: pick the format for the job · Art · Year 8

9 minutes

Part B: choose a format for each of the 5 Eco Club jobs

Each reason must use a number or a word from the stimulus sheet, not just a preference.

The job	Format	Reason
1. Litter-pick photograph on the website home page	JPEG	It is a photograph, so lossy is fine: 212 KB instead of 1.87 MB, and you cannot see the loss without zooming to 400%.
2. Logo on an A1 banner	SVG	Vector, so it stays razor sharp at any size. Also the smallest file on the sheet at 3 KB.

Part B on your worksheet · 9 minutes Prove the choice with a size or a quality note

Supply teacher script (no subject knowledge needed)

Say aloud: “9 minutes for Part B. Two rows are done on the board. For jobs 3, 4 and 5, name a format and give a reason with a real number or a word from the stimulus sheet.”

Quick check answers: Job 3 (logo on a dark green photograph): PNG, it needs a see-through background with soft edges; the JPEG turned the background solid white with grey speckles and was 94 KB against PNG’s 19 KB. Job 4 (spinning badge in the email): GIF, it must animate so PNG is out; WebP is smaller (96 KB against 480 KB) but some email programmes show it frozen. Job 5 (master copy to re-edit): PNG, lossless, so a JPEG re-saved over and over would turn to mush. Accept WebP for job 1 (138 KB) if the reason is sound.

Slide 5 of 7 · Parts C and D: the email sums and real exports · Art · Year 8

14 minutes

Part C: two email sums. Part D: export one image three ways

The school email will not send an attachment bigger than 25 MB. Take 1 MB as 1024 KB. Show your working.

C1 model: 25 MB ÷ 1.87 MB = 13.36, so 13 PNGs. Check: 13 × 1.87 = 24.31 MB fits; 14 × 1.87 = 26.18 MB does not.

C2: turn 25 MB into KB first (25 × 1024), then divide by 212 KB.

Part D (if you have a computer): save one photo as PNG, JPEG high quality and JPEG low quality. Record each size and what you see at 400% zoom.

Part C 6 minutes, then Part D 8 minutes No computers? Skip Part D and try the extensions

Slide 6 of 7 · Self and partner check · Art · Year 8

4 minutes

Swap and mark Part A against the success criteria

Swap worksheets with a partner. A wrong box is worth finding now. Tick each criterion only when you can prove it.

I can say which formats are lossy and which are lossless, and explain what is lost.
I can explain the difference between a bitmap and a vector, and why only one stays sharp on a banner.
I can name which formats support see-through areas and which support animation.
I choose a format for a real job and back it with a file size or a quality note, not just a preference.

4 minutes · partner check Finished? Write the two-line rule for above the class computers

Slide 7 of 7 · Plenary review · Art · Year 8

4 minutes

Quick-check answers before handing in

Check your main answers before your worksheets are collected.

Question	Correct answer
Which format is the only vector one, and how big was the logo in it?	SVG, 3 KB, razor sharp from a business card to a banner.
Which format can be saved either lossy or lossless?	WebP. Lossy at 138 KB for the photo, lossless at 14 KB for the logo.
How many 212 KB JPEGs fit in a 25 MB email?	120. 25,600 KB ÷ 212 KB = 120.75, and 120 × 212 = 25,440 KB fits.

Check your name and class are on your worksheet Leave stimulus sheets neat on the desk