Lehrveranstaltungsinhalt aus - Institute for Computer Graphics and ...

1.4. DISPLAYING IMAGES ON A MONITOR 41
Prüfungsfragen:
• Skizzieren Sie den Vorgang der Bilderkennung als Kette von Prozessen von der Szene bis hin
zur Szenenbeschreibung.
1.4 Displaying Images on a Monitor
The customary situation today is with a refresh buffer in which we store numbers and represent
the image. We will use a display controller that managers this buffer based on data and software
residing on a host computer. And we have a video controller that takes what’s in the buffer and
presents this information on a computer monitor. In the buffer we might have a binary image
at 1 bit per pixel. Or we may have a color image at 24 bits per pixel. These are the typical
arrangements for refresh buffers. The refresh buffer typically is larger than the information on
a computer monitor. The computer monitor may display 800 by 1000 pixels. The refresh-buffer
might hold 2000 by 2000 pixels. An image is displayed on the monitor using a cathode-ray tube
or as LCD-arrangement. On a cathode-ray tube the image is being painted line by line on the
phosphor is surface, going from top to bottom.
Then the ray gets turned off. So it moves from left to right with the beam-on, right to left
with the beam-off, top down with beam-on, down-to-top at beam-off. An image like the one in
Slide “Wiedergabe bildhafter Information” is a line drawing. How could this be represented on
a monitor? In the early days this was by a vector scan, so the cathode-ray was used to actually
paint vectors on the monitor. Very expensive vector display monitors where originally built maybe
as long as into the mid-80’s. The development of television monitors became very inexpensive,
but vector monitors remained expensive, and so a transition took place from vector monitors to
raster monitors, and today everything is represented in this raster. Vector scan) We could have
a raster display to present the contours of an object, but we can also fill the object in the raster
data format.
Not all representations on a monitor are always dealing with the 3-dimensional world. Many
representations in image form can be of an artificial world or of technical data, thus of non-image
information. This is typically denoted by the concept of “visualization”. Slide “Polyline” is a
visualization of data in one dimension. Associated with this very simple idea are concepts such as
polylines (representing a bow tie) and we have a table of points 0 to 6 representing this polyline.
There are concepts such as “markers” which are symbols that represent particular values in a two
dimensional array. This has once been a significant element in computer graphic literature that
today no longer represents a big issue.
Prüfungsfragen:
• Beschreiben sie die Komponenten, die in einem Computer zur Ausgabe und zur interaktiven
Manipulation eines digitales Rasterbildes benötigt werden.
• Beschreiben Sie unter Verwendung einer Skizze den Aufbau eines digitalen Rasterbildes auf
der Leuchtfläche eines Elektronenstrahlschirmes .
• Was ist der Unterschied zwischen Vektor- und Rasterdarstellung eines digitalen Bildes?
Veranschaulichen Sie Ihre Antwort anhand eines einfachen Beispiels und beschreiben Sie die
Vor- und Nachteile beider Verfahren.
• Erklären Sie anhand einer Skizze den zeitlichen Ablauf des Bildaufbaus auf einem Elektronenstrahlschirm!