Module 2 - Unit 1: Digital Content - Section C: Bitmap Graphics

CCD

(charge-coupled device). A CCD contains a grid of tiny light-sensitive diodes called photosites.

Photosites

A CCD contains a grid of tiny light-sensitive diodes called photosites. The number of photosites depends on the size of the CCD. A one-half-inch square CCD can contain more than 500,000 photosites. Each photosite detects the brightness and color for its tiny piece of the image A CCD's photosites correspond to pixels. The more pixels used to capture an image, the higher its resolution, and the better the resulting picture. Cameras with larger CCDs produce higher quality images. Some cameras contain multiple CCDs, which enhance the color quality of a camera's output.

Bitmap Graphic

A bitmap graphic, also called a raster graphic or simply a bitmap, is composed of a grid of tiny rectangular cells. Each cell is a picture element, commonly called a pixel. Each pixel is assigned a color, which is stored as a binary number.

Clipping Path

A clipping path essentially cuts an object out of an image and knocks out the background to make it transparent. This object can then be superimposed on a background.

Alpha Blending

Alpha blending alters the pixel colors where the edges of the object and the background meet, so that the object appears to merge with the background

Pixelation

As you stretch the surface, the grid maintains the same number of horizontal and vertical cells, but each cell becomes larger, the grid becomes more visible, and the image develops an undesirable jagged appearance referred to as pixelation. Simply stretching a bitmap to enlarge it doesn't produce highquality results

BMP

BMP, pronounced "bee-em-pee" or "bump," is the native bitmap graphics file format of the Microsoft Windows environment. Microsoft Paint, included as part of Microsoft Windows, creates BMP graphics files. The BMP format supports True Color and can be used for a wide variety of graphics applications, such as photographs, illustrations, and graphs. BMP files are often too large for email attachments. BMP graphics are not supported by most browsers, so they are not used on the Web. Graphical elements, such as buttons and other controls for graphical user interfaces

Image Histogram

Beyond one-click enhancement tools, image editors provide an image histogram that can be used to adjust the brightness values for various ranges of dark, mid-range, or light pixels

Resolution Dependent

Bitmap graphics are resolution dependent because each element is a discrete pixel.

Cloning

Cloning employs algorithms that pull pixels from one area of an image and then apply them to another area.

Color Model

Color values can be specified in decimal (base 10), hexadecimal (base 16), or binary (base 2). Even artists need to know their way around number systems! Decimal notation tends to be used within graphics software, and hexadecimal (hex) notation is common on the Web. Whichever notation is used, however, color data is ultimately represented as binary digits when it is stored and transmitted. In decimal, a pixel color is specified with values such as Red 238, Green 130, and Blue 238. In hexadecimal, each pair of digits refers to a color value. For example, the hexadecimal number for violet is #EE82EE. In binary, eight bits are used to represent the red value, another eight bits are used for the green value, and eight more bits are used for blue.

Digital Compositing

Digital compositing, which assembles several images into one. Compositing is achieved using two tools: clipping paths and alpha blending.

Pixel

Each cell is a picture element, commonly called a pixel. Each pixel is assigned a color, which is stored as a binary number.

GIF

GIF (Graphics Interchange Format), pronounced "gif" or "jiff," was specifically designed to create images that can be displayed on multiple platforms, such as PCs and Macs. GIF graphics are limited to 256 colors, but the format supports simple animations. Once a popular format for Web pages, GIF is being replaced by JPEG and PNG. Web graphics and simple animations

Image Compression

Image compression refers to any technique that recodes the data in an image file so that it contains fewer bits. Many bitmap file formats automatically apply compression to an image when it is saved.

True Color

Images that use 24 bits for each pixel have a color depth of 24. 24-bit color depth is also called True Color.

JPEG

JPEG (pronounced "JAY-peg"), which stands for Joint Photographic Experts Group, is a graphics format with built-in compression that stores True Color bitmap data very efficiently in a small file. The JPEG format is popular for Web graphics and for photos attached to email messages. When creating a JPEG or converting an image to JPEG format, you can control the level of compression and the resulting file size. The compression process eliminates some image data, however, so highly compressed files suffer some quality deterioration. General use, such as desktop publishing or Web pages, where flexibility in file size is important. JPEG files are compressed using lossy compression, so some quality is lost when the file is saved. When saving an image as a JPEG, you may be able to select a compression level. Take care with lossy compression to ensure that your image is not further compressed every time you save it

Run-Length Encoding

Lossless image compression. As a simple example, consider a type of lossless compression called runlength encoding. Run-length encoding (RLE) replaces a series of similarly colored pixels with a binary code that indicates the number of pixels and their colors.

Pixel Interpolation

Most graphics software uses a process called pixel interpolation to create new pixels by averaging the colors of nearby pixels. For some images, pixel interpolation produces an enlargement that appears very similar to the original. Other images—particularly those with strong curved or diagonal lines—may appear pixelated.

PNG

PNG (Portable Network Graphics), pronounced "ping," is a graphics format designed to improve on the GIF format. A PNG graphic can display up to 48-bit True Color (trillions of colors). Unlike JPEG, PNG compresses bitmap files without losing any data, so compressed images retain the same high quality as the originals. PNG was developed as a public domain format without any restrictions on its use. Web graphics and other general uses

RAW

RAW image formats contain the unprocessed pixel data generated directly by a digital camera's sensor. Up to 12 bits of data can be stored for each of the red, blue, and green values for a pixel, so RAW files are very large. Cameras that offer a RAW format also supply proprietary software to convert RAW data to JPEG or TIFF. Photographic images before they are stored in other formats

Inpainting

Reconstructing lost, unwanted, or deteriorated areas in a photo is called inpainting. Using information from nearby pixels, and taking into account the overall structure of the image, inpainting algorithms essentially scrub out designated areas and miraculously replace the missing pixels with a background or an object that fits with the rest of the image

TIFF

TIFF (Tagged Image File Format), or TIF, is a flexible and platform-independent graphics file format supported by most photoediting software packages. Scanners and digital cameras commonly store bitmaps in TIFF format because it supports True Color and can be easily converted into other graphics file formats. Desktop publishing and any projects that require highresolution graphics; not supported by browsers

Lossless Compression File Types

TIFF, PNG, and GIF graphics formats offer lossless compression. Images stored in these formats do not lose any quality when compressed.

RGB

The color displayed for a pixel is based on the intensity of red, green, and blue signals received by the screen's color elements. Each red, green, and blue signal is assigned a value ranging from 0 to 255: 0 represents the absence of color, and 255 represents the highest intensity level for that color. A pixel appears white if the red, green, and blue signals are set to maximum intensity. If red, green, and blue signals are equal but at a lower intensity, the pixel displays a shade of gray. A pixel appears violet if it receives high red and blue signals and just a bit of green

Image Resolution

The dimensions of the grid that forms a bitmap graphic are referred to as image resolution. The resolution of a bitmap is usually expressed as the number of horizontal and vertical pixels it contains. High-resolution graphics contain more data than low-resolution graphics. With more data, it is possible to display and print high-quality images that are sharper and clearer than images produced using less data.

Digital Camera

The lens of a film camera captures the light from an image onto a light-sensitive roll of film, which is developed to produce a photographic print. In a digital camera, the lens focuses light from the image onto a small image sensor called a CCD (charge-coupled device). A CCD contains a grid of tiny light-sensitive diodes called photosites.

Scanner

When you have a printed image, such as a photograph, a page from a magazine, or a picture from a book, you can use a scanner to convert the printed image into a bitmap graphic. A scanner essentially divides an image into a fine grid of cells and assigns a digital value for the color of each cell. As the scan progresses, these values are transferred to your digital device and stored as a bitmap graphics file.

Color Depth

With eight bits used to represent each color value, one pixel requires 24 bits. Because each R, G, and B can have 256 values, the number of possible colors is 16.7 million (256 × 256 × 256). The number of colors available in a graphic is referred to as color depth.