dcf.cymru stimulus sheet · Art and Digital Media · Year 8

One image, exported five ways

These are real export results. Nothing in the pictures changed — only the format they were saved in.

Export 1 — a photograph

Source: a photograph of Pen y Fan taken on a phone, cropped to 1200 × 800 pixels. That is 960,000 pixels. Stored with no compression at all, at three bytes per pixel, it would be 2,880,000 bytes — about 2.75 MB. Every row below is the same picture at the same size.

File	Size on disc	What it looks like on screen
pen-y-fan.bmp	2.75 MB	Perfect, and far too big to email or put on a website.
pen-y-fan.png	1.87 MB	Identical to the original, pixel for pixel. Still very large.
pen-y-fan.gif	604 KB	The sky has gone stripy. Smooth blue has turned into visible bands.
pen-y-fan.jpg (quality 80)	212 KB	Looks the same as the original unless you zoom to 400% on the skyline, where there is faint mush.
pen-y-fan.webp (quality 80)	138 KB	Same as the JPEG to the eye, in about two thirds of the space.

Export 2 — a flat logo

Source: the Eco Club logo — three flat colours, hard edges, some text, drawn with shapes rather than photographed. Exported at the same 1200 × 800 pixels, except the SVG, which has no pixel size at all.

File	Size on disc	What it looks like on screen
eco-club-logo.svg	3 KB	Razor sharp at any size, from a business card to a banner on the school gate.
eco-club-logo.webp (lossless)	14 KB	Sharp at 1200 × 800. Blurry if you blow it up to poster size.
eco-club-logo.png	19 KB	Sharp, and the background is see-through, so it sits on any colour.
eco-club-logo.gif	22 KB	Sharp, but the see-through edge is jagged rather than soft.
eco-club-logo.jpg (quality 80)	94 KB	Grey speckles round every letter, and the see-through background has turned solid white. Bigger and worse.

Export 3 — a short animation

Source: a 2-second spinning recycling badge, 24 frames, 400 × 400 pixels.

File	Size on disc	What it looks like on screen
spinning-badge.gif	480 KB	It animates, and it works everywhere, but it is limited to 256 colours per frame.
spinning-badge.webp	96 KB	It animates too, with full colour, at a fifth of the size.
spinning-badge.png	68 KB	One frame only. PNG does not animate, so the badge is frozen.

Five words you need

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.
Bitmap (raster) — the image is a grid of coloured pixels. Enlarge it and it goes blocky or blurry.
Vector — the image is a list of shapes and coordinates that the computer draws fresh every time. Enlarge it and it stays sharp.
Transparency (alpha) — the image can have see-through areas, so it sits on any background.

The jobs the class needs images for

A photograph of the Eco Club litter pick, going on the school website home page.
The Eco Club logo, going on an A1 banner for the school gate.
The Eco Club logo, going on top of a dark green photograph on a poster.
The spinning badge, going in the school newsletter email.
The master copy of an edited photograph, going in the shared drive so it can be edited again next term.