Bitmap Basics Review Refresher from Year 8

We’ll actually start this new unit by reviewing what we did last year. Review of Year 8 We’ll actually start this new unit by reviewing what we did last year. That will remind us about some basic ideas and some continuing themes… Hello, I’m Herman Did you Forget me?!

bitmap images binary data Review of Year 8 Last year’s focus was ‘theory’ with bitmap images and how they’re stored in files as binary data bitmap images binary data So we’ll quickly review the key points because they’ll help our practical work making memes…

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Review – Range of Images Our digital world is filled with all kinds of imagery, from photos & clip art through to animated films Bitmap Image Vector Image 3D Animation e.g. photos e.g. clip art e.g. movies We focused on photos because we all use them LOTS!

Review – Bitmaps & Pixels Bitmaps are a grid of tiny squares or pixels

Review – Counting Pixels How many pixels in this tiny sample? 15 pixels 10 pixels 15 x 10 = ? pixels 150

Review – Counting Pixels How many pixels in the whole photo? 3,519 pixels 2,345 x 3,519 = ? pixels 8,252,055 Imagine you took this photo & clicked ‘share’. How big would the exported photo be? million 8 megapixels 8 But many colours are there in our bitmap images?

Review – Counting Colours For example, think about the colour ‘blue’ That’s 29 ‘colours’ – just for ‘blue’ ! Each needs a unique binary colour code So the more binary bits you have… …the more colour codes you can use! Let’s recall why more bits is better…

bit byte 8 bits = 1 byte So how many colour codes can you have with one or more bytes…?

128 64 32 16 8 4 2 1 8 bits = 1 byte = = 1 1 = 1 2 = 1 1 3 256 values 128 64 32 16 8 4 2 1 = 255 1 1 1 1 1 1 1 1

8 bits 1 byte 9 bits 10 bits 11 bits 12 bits 13 bits 14 bits 15 bits 16 bits 2 bytes x2 256 values 65,536values x2 512 x2 32,768 1,024 16,384 x2 x2 2,048 8,196 x2 4,096 x2 x2

x2 x2 x2 x2 x2 x2 x2 x2 256 65,536values 16.7 million ? 131,072 1 byte 2 bytes 17 bits 18 bits 19 bits 20 bits 21 bits 22 bits 23 bits 3 bytes 256 values 65,536values 16.7 million values ? values x2 x2 131,072 8,388,608 x2 x2 262,144 4,194,304 x2 x2 524,288 2,097,152 x2 1,048,576 x2

Images, Pixels & Colours GIF JPEG 8 bits = 1 byte 24 bits = 3 bytes 256 16m Colours Colours

GIF JPEG GIFs & One Byte Sky & sea not ‘smooth’ More bits 8 bits = 1 byte 24 bits = 3 bytes Sky & sea not ‘smooth’ More bits GIF can’t do all colours So more colours ‘Posterised’ ‘True colour’ But can do animation!

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JPEGs & Three Bytes So each of the three primary colours can have a value from 0 to 255 You can write these colour codes in binary (eg 111111110000000000000000) Or you can use those hex codes like you can in Fireworks (eg FF0000) But it’s easiest to use decimal RGB codes… decimal RGB codes

Red Green Blue RGB (255, 0, 0) = ? Red R G B 255 1 1 1 1 1 1 1 1

RGB (255, 255, 0) = ? Yellow Red Green Blue R G B 255 255 1 1 1 1 1 1 RGB (255, 255, 0) = ? Yellow R G B 255 255 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

RGB (0,255, 255) = ? Cyan Red Green Blue R G B 255 255 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 RGB (0,255, 255) = ? Cyan R G B 255 255 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Your Book 255 255 255 Just so students know what’s coming up