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creating, modifying and communicating digital images
- retouching and enhancing photographs (color correction, removing scratches)
- editing photographs (adding and removing elements)
- painting (drawing line, shape, color and texture)
- montage (combining images)
- special effects (applying filters)
many disciplines that use visual communication make
use of digital imaging
- graphic design - examples one and two
- photography - examples one and two and three
- illustration - examples one
- fine art - examples one and two
- architecture
- engineering
- web design - examples one
digital imaging involves three processes
- acquiring the image
- manipulating the image
- outputting the image
getting the image into digital format
- digital camera
- scanning
- photo CD
- creating in application software
retouching, enhancing, compositing and applying special
effects to the image
- standard dark room techniques (cropping, dodging, burning, color balance, contrast)
- combining images
- painting
- special effects (blur, sharpen, distort, texture)
communicating the image
- printing (various technologies and media)
- exporting to other digital formats (e.g. desktop publishing, web)
- film (output to film with film recorder)
the two methods of graphic representions provide
very different kinds of manipulations
- vector graphics are made of objects that can be moved, copied, stretched
- bitmap graphics are made of pixels that can be painted, erased, overlayed
digital images are called bitmap (or raster) images
because of the way they are represented
- a pixel (picture element) is the basic unit of an image containing intensity or color information
- a bitmap is a matrix of pixels representing an image, arranged into rows, columns and levels
- a bitplane is a rectangular grid of pixels one bit deep
- a channel is a rectangular grid of pixels 8 bits (1 byte) deep, usually representing one color
resolution is the density of pixels, the number of
pixels in the rows and columns
- resolution is measured as pixels per inch (PPI) or dots per inch (DPI)
- higher resolution means better quality image and larger file size
- low resolution images have visible "jaggies" or stair steps in diagonal lines, curves and text
- it is important to use an appropriate scan resolution to obtain good image results
bit depth or color depth is the number of bits used
for each pixel
- bit depth determines the number of colors that can be represented in an image
- greater bit depth means more colors and larger file size
- images are often characterized by color resolution, for example 8-bit grayscale (256 grays), 8-bit indexed color (256 colors), or 24-bit color (16,777,216 colors)
- it is important to use a bit depth appropriate for output
there are various models used to represent color
- RGB model represents color using the additive primary colors of light
- CMY model represents color using the subtractive primary colors of pigment
- HLS model represents color using hue, lightness and saturation
each program has its own native file format, for example
photoshop uses PSD files and painter uses RIFF files, however there are
a number of standard file formats used to save and transfer images between
applications and devices
- file formats differ in the compression they use to reduce file size
- there are two basic types of compression, lossless (larger file size, no information loss) and lossy (smaller file size, information loss)
- TIFF (Tagged Image File Format) is a highly portable file format supporting many color models (RGB, CMYK, Indexed color and Grayscale) and alpha channels and using lossless compression
- JPEG (Joint Photographic Experts Group) supports 24-bit color, compressed photographic images and allows different degrees of lossy compression
- GIF (Graphics Interchange Format) is a popular web graphics format supporting transparency but is limited to 256 colors
- PNG (Portable Network Graphics) is a compressed image format for Web graphics, supporting lossless compression, 24-bit color, alpha channels and transparency
- PICT is a standard Macintosh RGB file format.
- BMP is a standard Windows RGB file format.
- PDF (Portable Document Formt) is a cross platform page description format containing raster and vector information, embedded fonts and other features
- EPS (Encapsulated PostScript) contains both raster and vector information and is used for print devices
the widespread use of digital imaging has implications
in the way images are used and perceived