AP CSP Unit 3

lossy compression

(or irreversible compression) a data compression method that uses inexact approximations, discarding some data to represent the content. Most commonly seen in image formats like .jpg.

lossy text compression

-mostly used in audio or video formats where a loss in precision is undetectable to human eyes and ears

gif

-uses a dictionary of up to 255 different colors -each pixel is stored as small number that refers to the dictionary. -a lossless format for image files that supports both animated and static images.

1 kilobyte

1024 bytes

1 megabyte

1024 kilobytes

1 terabyte

1024 megabytes

1 perabyte

1024 terabytes

image

A type of data used for graphics or pictures.

light

As you are about to see, with color, we actually use binary to encode the physical phenomenon of ________.

light, RGB

Computer screens emit _______, so when you mix ______ colors, you are really mixing light together

metadata

Data that describes other data. For example, a digital image my include metadata that describe the size of the image, number of colors, or resolution.

raster, raster, resolution

Digital images can be stored in many formats, but one of the most common formats is "______". _________ images store the image as an array of individual pixels, each of which has a particular color. Higher-quality images can be obtained by decreasing the size of the pixels (______).

hexadecimal, 4, compression

It is important to note that _________ numbers are used to aid humans in reading longer strings of bits, but they in no way change the underlying data being represented. Instead, they allow us to read __ bits at a time rather than 1, and so allow us to more easily parse binary information. Hexadecimal representation is NOT a form of ________, since the underlying binary representation is not changing at all. Rather it is a more convenient way of representing that binary information when humans need to read and interact with it.

height, width

Simply encoding the pixel data is not enough. We also need to encode the ______ and _____ of the image, or the image could not be recreated - other than through trial and error

3, grayscale

The Pixelation Tool is in RGB mode, as long as the number of bits per pixel is a multiple of ___ (3, 6, 9, 12, etc.) This allows for the same number of bits to be allocated to each color channel. Other bits-per-pixel settings will set the image to ______, with more bits allowing finer control over the shade of gray.

RGB, 0, 255

The ______ color scheme is composed of red, green, and blue components that have a range of intensities from _ to ____.

fewer, dictionary

The basic principle behind compression is to develop a method or protocol for using ______ bits to represent the original information. The way we represent compressed data in this lesson, with a "__________" of repeated patterns is similar to the LZW compression scheme, but it should be noted that LZW is slightly different from what students do in this lesson. Students invent their own way here. LZW is used not only for text (zip files), but also with the GIF image file format.

RGB, 24, hexadecimal

The most common color representation scheme - _______ - typically uses ___ bits (3 bytes) with 8 bits each for Red, Green and Blue intensities. And one of the most common ways you see these colors represented is in ______.

LZW, zip

There is a compression algorithm called ______ compression upon which the common "____" utility is based. Zip compression does something very similar to what you did today with the text compression widget. Here is an animation of lzw in action. You can see the algorithm doesn't compress it the most, but it is following a heuristic that will lead to better and better compression over time.

compress, algorithm

There is no single correct way to ________ text using the method we use in this lesson because a) there is no known _______ for finding an optimal solution, and b) we don't even know a way to verify whether a given solution is optimal. There is no way to prove it or derive it beyond trying all possibilities by brute force. This is an example of an algorithm that cannot run in a "reasonable amount of time".

metadata

We've seen forms of _______ before. For example: an internet packet. The packet contains the data that needs to be sent, but also other data like the to and from address, and packet number.

transformation

When an manipulation is performed on a digital image to compress the information (lossless or lossy) this is called a

screen resolution, density

_____________ is the number of pixels and how they are arranged vertically and horizontally, and _________ is the number of pixels per a given area.

file extensions

______you often see on a file (for example: myPhoto.jpg) is really just an indicator to the computer of how the underlying bits are organized, so the computer can interpret them. If you change the name of the file to myPhoto.gif, that does not magically change the underlying bits; all you've done is confuse the computer. It won't be able to open the file because it will attempt to interpret the file as a GIF when really the bits are in JPG format.

lossless compression

a data compression algorithm that allows the original data to be perfectly reconstructed from the compressed data

gif and bmp

photo formats

pixel

short for "picture element" it is the fundamental unit of a digital image, typically a tiny square or dot which contains a single point of color of a larger image.

RGB

the RGB color model uses varying intensities of (R)ed, (G)reen, and (B)lue light are added together in to reproduce a broad array of colors.

turn all lights off

to make black appear on computer screen

mix full red and full blue

to make pink appear on the computer screen

turn all lights on

to make white appear on computer screen

zip format

used for photos or text, but usually for text