Sheridan College
Architectural Technology
CADD12384 - Architectural
Drafting 2 - CAD
Overview - Raster
Images
Vector Image Files:
- file stores vector/geometric information about
the image or drawing
- pixel image on screen regenerated by software
program as objects modified
- resolution of the image depends on the configuration
setup of the software regenerating the onscreen image
- the size of the image is independent of the screen
resolution
- objects in such files can be scaled and manipulated
without losing detail or information
- generally smaller file sizes -vector based image
files:
- objects in 3D Studio MAX's 3D Workspace (max)
- AutoCAD drawing files (.dwg)
- some elements of Windows metafiles (.wmf)
Raster (Bitmap) Image
Files:
- a raster graphic image file format that consists
of an arrangement of pixels (picture elements) that represent an image
- these types of images are produced during Rendering
in 3D Studio or AutoCAD
- limited options with respect to editing
- several types of image formats available
Raster Bitmap Image File
Characteristics
a. Format
- different standards created by different program
developers
- usually referred to by their file extension
b. Image Size / Dimensions
- no. of horizontal pixels x no. of vertical pixels
in the image
800 x 600
640 x 480
320 x 200....
c. Colour Depth
- different formats of graphic image files have
different color information colour depth:
- 8-bits of color info. - limited to 256 colors
- use for computer presentations
- 16-bits -up to 64000 colours
- 24-bits -up to 16 million colours (.TGA or.TEF)
- also called truecolor files
- used for broadcast quality images
- can have an additional 8 bits of Alpha data that
provides transparency information (32-bit color) - RGB(A)
- colour depth affects image file size
Bitmap Image File Size
- some bitmap formats allow for storing in compressed
format to save disk space
- these files are uncompressed when read into RAM
- size of image files before compression approximates
to:
- 8-bit color depth = resolution x 1 (800 x
600 x I = 480,000 bytes = 480 Kb)
- 24-bit color depth = resolution x 3 (800 x
600 x 3 = 1,440,000 bytes = 1.44 Mb)
Raster Image File Formats
- .GIF
-
- 8-bit Graphics Interchange Format developed by Compuserve
- portable between all PCs
- Macintosh, Amiga, Atari, Apple 11 and IBM
- very efficient compression
- may be of any resolution
- used extensively on the Internet or in multimedia applications
- recent copyright and licensing rulings have resulted in Autodesk removing the
writing capabilities of AutoCAD and 3D Studio MAX to create GIF files
.TGA
-
- popular Targa Truevision format
- common with scanners, VGA capture boards
and rendering applications
- 8, 16, 24 and 32 bit RGBA formats
- compressed or uncompressed
- preferred rendering format for output to video
- .TIF
-
- compressed and uncompressed 32-bit RGBA Tagged
Image File Format (TIFF)
- often created with scanners or video capture boards
- many variations of format around with some possible
diiticulties with compatibility (largely related to compression techniques)
- mostly used in desktop publishing
- might use when sending image to a printing service
bureau
- .BMP
-
- Microsoft Windows bitmap format
- can be 8-bit (256 colour), greyscale and 24-bit
truecolor
- use if intend to import images into Windows based
paint programs
- .JPG
-
- format of Joint Photographic Experts Group
(JPEG)
- uses variable compression methodknown as
"lossy" compression
- because of loss of image quality as increase
compression
- Alpha not supported by JPEG
- can have high compression with barely noticeable
loss of quality
- good for storing mapping images
- used extensively on the Internet