Communicating Quantitative Information Is a picture worth 1000 words? Digital images. Number bases Standards, Compression Will [your] images last? Homework: (Post project proposal). Work on Project. Postings. Vote on Election Day.

Digital images Basic encoding –Is a picture worth 1000 words? Standards –bmp, gif, jpg Preservation issue –will the files last on storage medium –will there be appropriate software to display and manipulate the image

Basic encoding Divide image into picture elements (pixels) For each pixel (cell in the grid), record color –Different color spaces: palette-based RGB (redness, greenness, blueness) YUV (Y=brightness, U and V together are hue and saturation) other

Digital cameras marketing More pixels (increased resolution) means that pictures can be 'blown up' more without showing pixelations If you are NOT planning to make poster size pictures, you don't need more than 3megalpel? 5 megalpel? cameras now competing on features like modes

Palette based Think of painter's palette Can only use those colors If no match: –painter mixes up something (creates a new color on palette) –computer software dithers produces spots of different colors that, hopefully, our eyes mix together to see desired color.

The software constructs palette when saving this image using a format with limited palette

Image file Simple bit mapped, palette –(may include the palette, with general representation of the colors) –string of numbers, one for each pixel, indicating how that pixel is to be painted

Contrast Painter (in smock) starts with palette Computer software (PhotoShop, Paint Shop Pro, etc. doing conversions) can construct the best palette for a given photo

Encoding Image file is all numbers!! Actually, all bits (sequences of 1s and 0s) Suppose, palette is black and white –0 could stand for white –1 could stand for black Suppose, palette holds 4 colors –00, 01, 10, 11 represent 4 distinct colors Suppose, palette holds 256 colors – , , … There are 256 distinct patterns of 8 1s and 0s.

Quick exercise How many different patterns can be made using 0s and 1s, 3 bits long? Make a list 000

General formula Space N bits can hold 2 N distinct patterns 1 bit can hold 2 distinct patterns (represent 2 colors) bits can hold 4 distinct patterns (represent 4 colors) bits can hold 8 distinct patterns bits can hold 2 8

Image [file] size Say image is 300 by 400 pixels (300 wide, 400 high) Each pixel is 8 bits (so the picture can have 256 colors—not especially big) Say there is no compression (will get to this later) Size is 300 * 400 * 8 bits – bits

1000 words (Plain text file, not Word document) How big is a word? Assume it averages out to 6 letters. How many bits does a letter require? –In the standard encoding, 8 bits words occupies 1000* 6 * 8 = bits

Is a picture worth 1000 words? Answer: it better because it costs/takes considerably more space. compression reduces image sizes, but only so much

What is a K? Kilobyte of data –Byte is 8 bits of information: a piece of memory holding 8 slots, each a 1 or a 0. Kilo –Sometimes means 1000 –Sometimes means 1024 (2 raised to the 10 th power = 2*2*2*2*2*2*2*2*2*2

For purple hat

Compression 519 * 653 * 200 is This is roughly 100 times either 677 * 1000 is * 1024 is So… purple hat image is compressed (encoded) to take advantage of similar line sections of color. The gif format does this.

Digital camera Uses a (large) palette Records a number for what will be each pixel There may be settings for color depth (amount of bits ~ numbers of colors) and resolution (size of pixel)

Standards (briefly) gif: uses common strings, so repeated patterns do get compressed –compression is lossless. Can restore full detail. –restricted to 256 colors –Good for line art jpg: uses common areas, but in a different color space and a different way (approximates changes in 8 by 8 blocks). For example, detects common levels of brightness. –compression is lossy. Cannot restore full detail. –can hold millions of colors: 8 bits for each of YUV. –Good for photographs

Number bases Refresher: we use the decimal system: base 10 –10 distinct symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 –Base system first column on the left is the ones/unit place (10 0 ) second column starting from the left is the 10s place (10 1 ) third column is the 100 th place (10 2 ) and so on…

Base 2 Binary number system –have 2 symbols: 0 and 1. These are called bits! –Base system first column on the left is the ones/unit place (2 0 ) second column is the 2-place (2 1 ) third column is the 4-place (2 2 ) and so on Fewer symbols (simpler circuitry), longer strings of symbols needed

Warning bit is either a 0 or a 1. Abbreviation b byte is 8 bits. Abbreviation B k may mean 1000 or 1024 (a power of 2) Mega-bit, Mega-byte, Mega-pel bits, bytes or pixels… Gigabyte:

Base 16 Hexadecimal – 16 symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. –first column is the 1s place –second column is the 16 th place –third column is the 256 th place –and so on.

Exercise Write your age in –decimal –binary –hexadecimal How many 16s are there (probably just 1)? What is left over?

Use of Hexadecimal RGB colors –Each of red, green, blue is allocated 8 bits takes up 2 hexadecimal digits (bad term) –Deep red is FF0000 –Deep blue is 0000FF –white is FFFFFF –black is

Will digital images last Depends on storage medium. Hard disks can fail. CDs and DVDs can get damaged. Memory sticks fairly robust, but ends can get damaged (and they can get lost) software: Need software that 'knows' the standard used for the picture –Software for display, manipulation, printing

Sound Sound files also come in different formats. –wav (different parameters) –mpeg –ogg Browsers recognize different formats Same issue regarding archiving –Storage needs to remain –Software to manipulate and play needs to be available New formats still under development.

HTML5 fragment hithard.ogg hithard.mp3

Video Video (animation) is sequence of still images shown in rapid succession. LARGE data files Compression possible per frame and from frame to frame. Multiple compression schemes exist and still others under development.

HTML5 fragment sfire3.mp4 sfire3.theora.ogv sfire3.webmvp8.webm Your browser does not accept the video tag.

Homework Project I Postings –Posting topic: problems in archiving digital images –Old issue: major patent dispute concerning gif