A Primer for the Multimedia Curious
Episode I: Scanning Basics: Understanding Digital Graphics
As guided by Jared Alexander Seay of the College of Charleston Library.
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Multimedia
Madness:
A Primer for the Multimedia Curious Episode I: Scanning Basics: Understanding Digital Graphics As guided by Jared Alexander Seay of the College of Charleston Library. |
This site is designed as an aid to the session that I teach on Scanning Basics. It provides the basic information necessary to understanding concepts related to digitizing images with a scanner. Certainly, one can fling a picture on a scanner bed, push the scan button and walk away with a usable image. Most folks scan all the time with no idea of the difference in resolutions, color, the meaning of different image files, or why an image looks the way it does. The recent deluge of plug-and-play, push button scanners has made scanning a "no-brainer."
Yet, knowledge of
what is actually occurring and why can make you more effective in manipulating
the result. Knowing something as simple as the difference between
when to save an image as a GIF file and when to save it as a JPEG file
can “save” you lots of time (not to mention disk space). Before this
is over, you should understand not only the different file types, but also
the basics of resolution and color of digital images. In the last
section I also give step-by-step instructions on scanning an image.
I.
How an Image Looks and Why
How an image looks too you on the computer
screen is a combination of both the number of colors displayed (in the
graphic and/or the monitor) and the resolution (of the graphic and/or the
monitor). Color is determined by the bit depth of both the graphic
and the monitor. Resolution is a function of the pixels per inch
(ppi) of the graphic itself and by the pixels per inch (ppi) of your monitor.
The screen area of your monitor determines its ppi. Confused yet?
No worries. It only gets easier from here. We'll look at some
of the details below. But, in practice it is only necessary to have
a basic understanding of these concepts in order to get good scanning results.
Color
Color viewed on a computer screen is RGB.
The monitor creates the colors you see by emitting varying intensities
of red, green, and blue light. The colored lights overlap each other
allowing the display of millions of different color combinations.
Bit Depth and Color Display
A bit is the smallest unit of information
that a computer understands. Each bit (electronic pulse) can provide
only two pieces of information (on or off / 1 or 2 / black or white).
The term "bit depth" is used to describe the number of colors a graphic displays or the number of colors a monitor has the ability to display.
Bit depth is simply the number of bits
that a single pixel generates. For example, in a 1-bit monitor a
pixel can generate 2 colors (2 to 2nd power). In a 4-bit monitior
a pixel can generate 16 colors (2 to the 4th power).
| More information than you probably want to know:
Remember that each bit provides 2 pieces of information. Thus, to compute how many colors a particular bit depth will display, you simply multiply 2 to the power of the bit depth. For example a 4-bit monitor displays 2 to the 4th power, which is 16 colors. |
Bit depth can refer to either a graphic
("an 8-bit graphic") or a monitor ("a 24-bit monitor"). How does
this affect the real world in which you live? Simply this way:
the higher the "bit depth" of a graphic the more colors it displays.
The higher the "bit depth" of a monitor the more colors it is capable of
displaying.
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| 24 bit color displays 16.7 million colors |
Playing with it yourself
How Different Bit Depths
and
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You
can easily see the difference between differing bit depths by changing
the display settings on your monitor.
If you have a Windows PC, go to your monitor display settings. (From your START button select SETTINGS and then CONTROL PANEL). Then choose DISPLAY. From here choose the SETTINGS tab. You will be able to change your color display from 16-bit to 32-bit (depending on your system). You will also be able to adjust your screen area, which will affect your resolution. More on resolution below. |
Resolution of images: Monitor vs print
Printer Resolution
300 dpi
600dpi
Monitor Resolution
MAC: 72 ppi
PC: 96 ppi
When saving graphics for monitor display (web, presentation) save to no more than 96 ppi because the screen cannot "resolve" a greater count than that. Your files will be much smaller and the image resolution will be at its maximum (for a monitor). Also, low res ensures that anyone who "borrows" your image can not use it to print things like t-shirts, posters, or brochures.
How "resolved" an image appears on the
screen is a combination of "bit depth" and the monitor settings
Monitor Resolution Settings
Total pixels:
640 X 480 = lower resolution (less ppi,
image is bigger)
800 X 600
1024 X 768 = higher resolution (more ppi,
image gets smaller)
Relationship between pixels and color
The most important setting determining
how "resolved" a graphic looks is the number of colors. If your monitor
can only display 16 colors, then the graphics will appear to be lower resolution
even if you have the pixels set to a "higher resolution."
Remember, the amount of pixels you display also directly influences the number of colors you can display. The color depth also depends on how much RAM you have on your computer.