MMS1-Graphics & Images(chap.4)

Color Schemes

(also called color space, models or formats) have been developed to represent color mathematically.

Graphics Interchange Format (GIF)

-8-bit per pixel, bitmap image format commonly used by the world wide web. -Uses lossless compression technique. -Compress line art well -image can have transparent portion -Interlaced images possible -Animation possible (Jasc Animation Shop ) -Can only have a maximum of 256 colors -Does not compress photographs well -Copyrighted format such that developers must pay royalty

Joint Photographic Expert Group (JPEG)

-Commonly used standard method of compression for photographic images. -Support a maximum of 16.7 million colors Compresses photographs well -Possible to select compression ratio versus quality -Progressive (interlaced) images possible -Lossy compression technique: Losses some image information. -Degradation of image possible with repeated editing and saving -No transparency -No animation

Color resolution

-Each pixel can represent at least 2 possible colors or more. - color depth/channel depth is measured in bits.

Windows Bitmap (BMP)

-Most common format containing pixel by pixel value. -Platform independent -Support up to 24-bit color depth -No compression -A 32-bit version with integrated alpha channel has been introduced with Windows XP. (support transparency) -No animation

Portable Network Graphic (PNG)

-No color information lost -Can use all color depth - supports more than 16.7 million colors -Compresses well- Lossless Compression Technique -Image can have transparent portion -No animation

Binary (Bitonal) Image

-These images have two possible values of pixel intensities: black and white. -Also called 1-bit monochrome image, since it contains only black and white. -Typical applications of bitonal images include office/business documents, handwritten text, line graphics, engineering graphics etc. -The scanned output contains a sequence of black or white pixels. Binary 1 represents a black pixel and binary 0 represents a white pixel.

Color Image

-They are characterized by the intensity of three primary colors (RGB). -For example, 24-bit image or 24 bits per pixel. There are 16,777,216 (224) possible colors. In other words, 8 bits for R(Red), 8 bits for G(Green), 8 bits for B(Blue). -Since each value is in the range 0-255, this format supports 256 x 256 x 256 or 16,777,216 different colors.

Grayscale Image

-They contain several shades of grey. -Typical applications of grayscale images include newspaper photographs (non-color), magnetic resonance images and cat-scans. -An uncompressed grayscale image can be represented by n bits per pixel, so the number of gray levels supported will be 2n. -For example, 8-bit Grayscale Image. It consists of 256 gray levels. A dark pixel might have a pixel value of 0, a bright one might be 255.

YUV Color Scheme

-This is the basic color format used by composite color TV standards (NTSC, PAL and SECAM). -Y represents the luminance/brightness and can be thought of as containing black and white or gray-scale information. -U and V carry the chrominance or color information. There are a variety of YUV-like color models. -The advantage of using YUV for broadcast is that the amount of data needed to define a television picture is greatly reduced. -The disadvantage is that many colors that appear on a computer display cannot be recreated on TV.

RGB Color Scheme

-This model is convenient for CRTs since the numeric values can be easily mapped to voltages for the R, G, and B guns. -Any color can be defined by giving its R, G and B values, or coordinates, (red,green,blue). This is referred to as an ordered triplet.

Display Resolution:

-can refer to quality capability of graphic output (monitor). - is also measured in pixels in terms of height and width. -It simply means how many pixels can be displayed on the computer screen. -normally uses a setting of 640x480(VGA), 800x600 (SVGA), 1024x768, etc. -is bigger than the display resolution, the result would be part of the image will be out of the display area.

Image Resolution

-often associated with an image's degree of detail or quality. -measures the pixel dimension of an overall image or how many pixel the image has. -is measured in width and height. -100 * 100-pixel image has a total of 10,000 pixels

CMY/CMYK Color Scheme

-scheme is widely used for color printing. To print a particular color on a white page, one must apply inks that subtract (absorb) all colors other than the one desired. -Cyan, magenta, and yellow are the subtractive primaries and are the complements of red, green and blue. Color is specified by what is subtracted from white light (which is the sum of R, G and B). -Cyan subtracts red from white, and so on. Therefore, white can only be generated on white paper. The conversion between RGB and CMY can be done by using :

1.RGB Color Scheme 2.CMY or CMYK Color Scheme 3.HSB or HSI (Hue,Saturation,Brightness/Intensity) Color Scheme 4.YUV Color Scheme

4 commonly used color schemes

RAW Graphics File Format (.raw)

A flexible basic file format for transferring files between applications and computer platforms. This format consists of a stream of bytes describing the color information in the file.

Thresholding

A pixel is set to 1 or 0 depending upon whether it is above or below the threshold value. This creates monochrome (binary) images which are often used as masks when compositing*.

RGBA / 32-bit images

An important point: many 24-bit color images are actually stored as 32-bit images, with the extra byte of data for each. Allows RGBA color scheme; Red, Green, Blue, Alpha. Pixel used to store an alpha value representing the degree of "transparency".

Z Soft Paintbrush (.pcx)

Bitmap graphics file format, originally developed by Z-Soft for use with PC-Paintbrush. This file format is now used and generated by many applications and scanners.

1.Windows Metafiles (.wmf) 2.Adobe Illustrator file (.ai) 3.CORELDraw file (.cdr) 4.Enhance Metafile (.emf) 5.Encapsulated PostScript file (.ps) 6.Macromedia FreeHand file (.fh) 7.Macintosh PICT (.pic or .pct) 8.ShockWave Flash (.swf) 9.Scaleable Vector Graphic (.svg)

COMMON VECTOR FORMATS:

HSB/HSL Color Scheme

Computer monitors display colors by emitting color dots (red, green, blue). -Creation of color is based on function of three characteristics: > hue, saturation & brightness / lightness. (HSB / HSL) -Colors are represented by a triplet representing hue (hue is dominant color of a sample and is represented by an angular value varying from red to green to blue at 120° intervals), saturation (purity of the color) and brightness (luminance, or intensity of the color).

Truevision Targa (.tga)

Developed by Truevision Inc. TGA files is a file format that will support images suitable for display on Targa hardware but is supported by many applications on a wide range of platforms.

1.The height of the graphics 2.The width of the graphics 3.The color depth or bit depth

Factors to consider:

-Editing -Point operations -Filtering -Compositing -Geometric transformations -Conversions.

Image processing operations categories

Hue

It is the color sensation produced in an observer due to the presence of certain wavelengths of color. Each wavelength presents a different hue. Hue is based on a vector value moving from 0 to 360 degrees on a color wheel.

1.Truevision Targa (.tga) 2.Tagged Image File Format (.tif, .tiff) 3.RAW Graphics File Format (.raw) 4.Z Soft Paintbrush (.pcx)

Other Graphic File formats:

1.Macromedia Freehand MX 2.Macromedia Flash MX 3.Adobe Illustrator

Packages that allow to create vector graphics include :

1.Adobe Photoshop 2.Paint Shop Pro

Software to edit bitmapped graphics are :

1.GIF (Graphics Interchange Format) 2.Bitmap 3.PostScript 4.JPEG 5.TIFF (Tagged Image File Format) 6.TGA (often called Targa) 7.PNG, and etc.

Some examples of image file formats used for storing images are:

Editing

The most basic operation is changing individual pixels. Image editors also support cutting, copying, and pasting selected groups of pixel. A selection might be a simple rectangular sub-image or an arbitrarily shaped region. Selections are either drawn by the user or calculated by software (for instance, by examining color differences between neighboring pixels).

Bitmap graphics

The most common and comprehensive form of storage for images on computers is bitmap image. Bitmap use combination blocks of different colors (known as pixels) to represent an image. Each pixel is assigned a specific location and color value. There are also called pixelized or raster graphics.

1.Color resolution 2.Image resolution 3.Display resolution

There are three types of resolution measuring different aspects of the quality, detail and size of an image:

Saturation

This is a measure of color intensity, for example, the difference between red and pink. Although the two colors have the same predominant wavelength, one may have more white color mixed in with it and hence appear less saturated. (100% = pure color, 0% = black, white , gray)

Intensity / Luminance or Brightness

This is a measure of the light emitted or reflected by an object. Certain colors appear brighter than others as the human eye does not respond in the same way to all colors. The human eyes see finer details in image scene more because of brightness variations than because of color variations.

1.Bitmap graphics 2.Vector graphics

Types of Graphics

Vector Graphics

Vector images are based on drawing elements/objects to create an image. -The elements and objects are stored as a series of command that define the individual objects.

Conversions

With the variety of image formats available, there is a frequent need to convert from one format to another. Fortunately, there are a number of public domain software packages which handle many format conversion tasks. In addition, image processing software will usually import and export images in a number of formats. Besides format conversion, there are other operations that can be considered forms of conversion. These include image compression or decompression, changing color schemes (or models) and changing image depth or resolution.

pictures

are found in the world which is external to the computers.

images

are the 2-Dimensional digital representations of pictures found in computers. -Computer attempts to duplicate the "look and feel" of a picture via storing and processing. -Therefore, an image is a "realistic" version of the original picture ; dependant on the quality and capabilities of the computer and the graphic artist's ability to use the software.

Point Operations

consists of applying a function to every pixel in an image (or selection). The function is such that in calculating a new pixel value, the only image data used is the pixel's current value and exclude the neighboring pixels.

Compositing

creating new images or moving images by combining images from different sources - like real- world digital video, film, synthetic 3-D imagery, 2-D animations, painted backdrops, digital still photographs, and text.

Color Resolution / Color Depth

describe the number of bits used to represent the color of a single pixel.

-Photographs -Drawings or Line arts -Clip arts -Buttons and Banner -Charts and graphs -Backgrounds -Icons

graphic is a broader and general definition which includes:

Color correction

image may be modified to increase or reduce contrast, brightness, and to strengthen or weaken particular colors.

Geometric Transformations

include displacing, rotating, mirroring, and scaling an image. Other geometric transformations include skewing (slanting) and warping (an example of warping is mapping a rectangular selection to an arbitrary four-sided polygon)

graphic

is a broader and general definition which includes: -Photographs -Drawings or Line arts -Clip arts -Buttons and Banner -Charts and graphs -Backgrounds -Icons

image

is a spatial representation of an object or a scene. (image of a person, place, object)

Tagged Image File Format (.tif, .tiff)

is mainly used for exchanging documents between different applications and different computer platforms. It supports the LZW method compression for image types.

Compositing

is the combination of two or more images to produce a new image. Alpha channels are frequently used to control blending and masking. In general, compositing is specified by mathematical relationship between the various images. For instance one image might be produced from the sum of two existing images. A very large variety of effects are possible.

filtering

like point operation, involve applying a function to every pixel in an image or selection. The function determines a pixel's new value based on its current value and that of neighboring pixels. Depending on the definition of the function, filtering is used to blur or sharpen the image, introduce distortions, and produce a variety of special effects.

Image processing operations

may operate directly on pixel data or on higher level features such as edges, surfaces, and volumes.

Color Dithering

the process through which colors are changed to meet the closest available color based on the available palette