Transcript grc 175 intro - Computer Graphics Home

GRC 175
Computer Graphics Review
•Review of computer graphics concepts
•Review of Photoshop, Illustrator, Fireworks
•Review of scanning concepts
•HTML and CSS introduced
Bitmap vs Vector Graphics
Bitmap
•Image is composed of pixels
•Each pixel can represent a dif color
•Not ideally up-sizeable or scalable
•Used in painting programs like Photoshop
•Also known as a raster graphic
Vector
•Image is determined by a mathematical algorithm
•Uses mathematical relationships between points and the paths
connecting them to describe the image
•Vector graphics are composed of paths
•Scalable (up-sizeable)
•Used primarily in drawing programs like Illustrator, Flash
Bitmap / Raster Graphic
•Made up of pixels (pixels, smallest element of resolution on the
computer screen)
•A pixels is often referred to as a dot but is actually square
•Each pixel is represented by a shade of color
•Bit depth determines the possible shades of color available
•A bit depth of 4 (2 to the 4 power) = 16 colors possible
•8 bit color (28 = 256 colors)
•24 bit color (224 = 16,777,216 colors)
•Recommended color mode for screen design is RGB
Bitmapped
Image aliasing can be a problem when using bitmaps
Aliasing
Jagged edges (aka stair-stepping) can be apparent when there
are diagonal lines or curves in the image
Anti-aliasing
Attempts to smooth out the rough edges by blending edges by
adding the appearance of a shadow to hide sharp edge
Photoshop
"bitmap" image editor
… used for creating, modifying and outputting digital images of a
photographic nature, …manipulates individual color pixels within
a fixed bitmap.
…also referred to as a “painting” program.
Continuous tone images (photo quality images) are edited in
Photoshop.
Adobe Illustrator
“vector-based” drawing program
Vector graphics are composed of paths
You draw a path (line) by creating two anchor points
There are two types of anchor points:
corner (makes a straight line)
curved(makes a curved line).
In order to make a path/line you need two points
Adobe Illustrator cont.
You can create a curved line by generating curved paths (Bezier
curves) connected by modifiable anchor points.
…anchors, with their handles are editable, and never "leave" the
file.
Pulling and moving the handle on a curved point determines the
curve that is produced between two points.
Vector to bitmap
The process of changing a vector graphic to a bitmap image
is called rasterization
…converts the graphic's paths into pixels.
RGB color model
•Each pixel's color sample will have three numerical RGB
components (Red, Green, Blue) to represent the color
•Pixel color is made up of three projected colors of light that mix
together optically
•Projected light colors are red, green blue
•Mixed together these three colors create a color space called
RGB
RGB color model
•Screen-based color for screen delivery
•RGB color is additive, meaning that mixing all the colors creates
white
•The RGB color space was created for computer graphics to be
viewed only onscreen
RGB color model
•What you see (as far as color on your screen) is not always the
color that others will see on theirs
•Unpredictable color differences due to monitor settings and
calibrations
•Calibration is how your monitor displays images
•No universal calibration model for screen-based color
RGB color model
•Macintosh images typically appear much darker on
Windows systems due to gamma settings
•Gamma settings Windows ~2.2 vs Mac ~1.8
Hexadecimal-based colors
•Used for defining color in HTML
•Hexadecimal values are based on base-16 mathematics
•Graphics editors simplify this by showing us the colors to
choose from and not having to know their Hex number
Hexadecimal-based colors cont.
• Hex value starts out with #
•Sample hex value #aaffqq
•There are sixteen color names that can be alternatively used
instead of the Hex value, these names give us only basic colors like
Black, Blue, Red, White, Yellow, etc
Scanning
• When scanning, set the dpi to your desired scan level/quality
• DPI dots (pixels) per inch
• Image size, quality, and file size varies with scanned dpi
resolution
• 100-300 dpi is typical for scanning, depending on desired
quality setting
• Use RGB color mode for screen output
• Each pixel's color sample will have three numerical RGB
components (Red, Green, Blue) to represent the color
• If the web will be the final output then 72 dpi will be the final dpi
when we do a “save for web” in Photoshop, auto adjusted in
Photoshop
Scanning Recommendations Using Photoshop
•Open Photoshop (Use Photoshop to scan image )
•File>Import (look for scanner or driver name)
•Set scanning preferences
Set dpi to 300dpi
Select dpi based on desired quality/use
•300dpi for archival quality
•Preview Scan
•Crop image
•Scan image
•Save in Photoshop
(save a archive file .psd format)
Photoshop image export for web
•File>Save for Web
•Select GIF for line art/text/logo (up to 256 colors)
OR
•Select JPG or PNG for photographs, images, gradients (over
256 colors)
•Photoshop automatically adjusts resolution to ~72dpi
•Click on Save
Native Photoshop file is .psd
Exporting out of Photoshop to a common image format like
gif, jpg, png flattens the exporting image file (flattens layers)
.gif good for flat, solid colors. Contains up to 256 colors,
limited color range. Good for type, line art, and images with
sharp edges.
.jpg good for continuous tone images such as photographs
or an image that contains a variety of shades, gradients, or
blends.
.png also good for continuous tone images such as
photographs, newer file format, combines the best of the two
original common image formats
Dithering used with gif
•Creates the illusion of additional colors by positioning different
colored pixels in order to simulate a color that does not exist on
the 256 color palette
•Avoid dithering when possible
•Increases the file size slightly
•Can help when displaying gradients for gif images
Diffusion used with gif
•Helps simulates shades of colors for 8 bit 256 limited color display
•Produces a less obvious result while maintaining a small file size
•Higher percentages of diffusion do a better job of simulating
shades of colors
Image compression types
•Lossy: Some image data is lost in exchange for making the file
size smaller (compressing)
•Lossless: allows the exact original data to be reconstructed from
the compressed data
Transparency options
•There are options available to preserve transparent parts of
an image
•Transparent parts appear as grey/white checkerboard in
Photoshop background
•When “saving for web” save as transparent gif or ping and
select the transparency option
•Preserves the transparency in the original image or allows
you to define the color which should be used for
transparency
Gif animation
•Animated format using the gif image file format
•Suitable for web, no plug in needed for viewing of animation,
plays within browser
•Photoshop enables you to build animation and save in the
animated gif format
•Rarely used anymore, Flash is a competing file format that
requires a plug-in but offers more options
Browser/Web safe palette myth
The only reason to use the browser-safe palette is if you
have a concern that your Web design work will be viewed
from a 256 color (8-bit) computer system, extremely rare.
The Browser-Safe Palette only contains 216 colors out of a
possible 256. That is because the remaining 40 colors vary
on Macs and PCs. By eliminating the 40 variable colors, this
palette is optimized for cross-platform use.
The Browser-Safe Palette should not be used to remap color
photographs.
http://www.lynda.com/hex.html
Web Graphics File Formats
The three most popular image file formats for Web
use
JPG
GIF
PNG
Web Graphics Resolution
72 dpi dots / pixels per inch
(Recommended setting for web graphics)
Use pixels as your standard unit of measure when working in
editing programs such as Photoshop and Illustrator
When scanning you may want to scan at a higher DPI if you
plan on using a high resolution or needing a large image or for
non web or for print
Web Graphics Compressed File Formats
.jpg
•Photographs, gradients and textures with more than 256 colors
•Uses lossy compression, throws out data
.gif
•Logos and Text
•Supports transparency
•GIF format supports GIF animation aka. Animated GIF
•Uses lossless compression no data loss yet compressed
.png
•Originally meant to replace GIF
•Includes most features of GIF and JPG
•32 bit color transparency, alpha transparency, no animation
•Not supported in older browsers
•Uses lossless compression no data loss yet compressed
HTML overview
HTML tags
Relative vs Absolute images/links
Deprecated vs obsolete tags
CSS in future/advanced development
Minimum Required HTML tags:
(case sensitive in newer HTML, but must go in this order!)
<html>
<head>
<title>
</title>
</head>
<body>
</body>
</html>
Creating a webpage using HTML tags
• A webpage is a plain text document, contains all the
required HTML tags, and saved with the .html file extension
• Tags can be typed in TextEdit or any plain text editor like
Notepad and document is saved as anyname.html
• Most HTML tags have opening and closing tags
• Tags are used to markup text to have a desired format
Creating a webpage using HTML tags cont.
• Extra lines or extra character spacing is ignored
• Tags can be nested, must be ordered correctly
<p><em>bold text here</em></p>
• Tags were case insensitive (upper, lower or mixed)
although the newer standards XHTML and after will now
require all lower case (except DOCTYPE declaration)
Sample HTML tags, go inside body
• Hyperlink
<a href="URL goes here">Type a name for the link</a>
• Image
<img src="image filename location goes here" />
• Line Break
<br />
• Paragraph
<p>paragraph content goes here</p>
• Bold
<strong>bold text ges here</strong>
Relative vs Absolute images/links
•Important concept of files and important in web development
•Relative path (relative to wherever you are)
For example
/images/i.gif
(reads …look for a folder called images and inside the folder find file
i.gif)
•Absolute path (absolute path to location)
For example
http://www.art.com/images.i.gif
Client server computing
•Client is the one viewing or connecting to remote file
•Server is where files are stored
•Client is the program like Internet explorer being used to connect
to your webpage, each individual web browser is referred to as the
client
•Server is the web server which serves up files such as webpages
Web files overview
•The web has become a very common way for publishing files
•Need to understand URL addresses
•Relative vs Absolute images/links
URL
•Uniform resource locator, URL
•Web address for an online file
•Important concept of web files
•Absolute path (absolute path to location)
For example
http://www.art.com/images.i.gif
Files, Folders & Directories
•Another important concept of files and web
•Files such as online web pages and online images are stored in
directories
•Within directories we can have folders
•Folders can have sub folders
•Must keep highly organized when creating websites
•Organize your content into logical folders
Dreamweaver
•Dreamweaver is a software program used to author webpages
and very useful as a Website management tool, aka “wysiwyg”
editor, what you see is what you get
•DW has a built in FTP program
•FTP used to connect to a remote web server
•FTP, File transfer protocol
•You must first define your sites (within Dreamweaver) on each
machine you author on before you can FTP into a remote site
The World Wide Web Consortium (W3C)
W3C develops interoperable technologies (specifications,
guidelines, software, and tools) to lead the Web to its full
potential. W3C is a forum for information, commerce,
communication, and collective understanding.
The World Wide Web Consortium
http://www.w3.org/
Deprecated vs Obsolete
•
Deprecated means outdated and may soon become
obsolete (will probably continue to display by browsers)
•
Obsolete means it is no longer supported and may not be
recognized (by browsers or interpreters)
•
An obsolete element or attribute is one for which there is no
guarantee of support by a user agent
•
Obsolete elements are no longer defined in the specification
W3C standards
Deprecated
A deprecated element or attribute is one that has been outdated by
newer constructs. Deprecated elements are defined in the reference
manual in appropriate locations, but are clearly marked as
deprecated. Deprecated elements may become obsolete in future
versions of HTML. User agents should continue to support
deprecated elements for reasons of backward compatibility.
Definitions of elements and attributes clearly indicate which are
deprecated.
This specification includes examples that illustrate how to avoid
using deprecated elements. In most cases these depend on user
agent support for style sheets. In general, authors should use style
sheets to achieve stylistic and formatting effects rather than HTML
presentational attributes. HTML presentational attributes have been
deprecated when style sheet alternatives exist (see, for example,
[CSS1]).
Obsolete
An obsolete element or attribute is one for which there is no
guarantee of support by a user agent. Obsolete elements are no
longer defined in the specification, but are listed for historical
purposes in the changes section of the reference manual.
DEPRECATED Tags
The following HTML page illustrates the use of the deprecated HTML
attributes. It sets the background color of the canvas to white, the text
foreground color to black, etc.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>a study of population dynamics</title>
</head>
<body bgcolor="white" text="black"
link="red" alink="fuchsia" vlink="maroon" >
... document body goes here...
</body>
</html>
CSS Cascading Style Sheets
•
The presentational attributes of HTML have been deprecated
and replaced with CSS
•
CSS now the preferred way to specify a HTML document's
presentation, or style a webpage
<style type="text/css">
body {
background-color: black;
}
</style>
This webpage has an internal style sheet being applied. The style
sheet has a style for the body tag, it is adding a background color of
black to the body, this style is also referred to as a rule
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01
Transitional//EN” "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>a study of population dynamics</title>
<style type="text/css">
body { background-color: black; }
</style>
</head>
<body>
... document body goes here...
</body>
</html>
We will learn more about HTML and CSS during the semester.
This concludes our CG Review.
Please bring up any questions if at this time if you do not understand
any of the basic computer graphic concepts we have reviewed.