Page 17 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Unit 1: Fundamentals of Computer Graphics

is relatively simple. Early computers used mostly flashing lights, with punched cards or paper Notes
tape for input and output. When there is only room for a few hundred instructions, you take
input and output in its simplest form. But sometimes the available technology drives applications,
and sometimes, the need to do something becomes a driver of looking for new technology.

The latent for getting a computer to produce a picture of the data was not missed. It would be
more valuable if the picture were produced rapidly enough for the user to interact, but even
producing an image of some sort that represented the computer contents or calculations in the
recent past had its merits.
IBM was offering an output printer on its 701 model in 1952. It also offered a primitive graphics
solution (the model 740 “Cathode Ray Tube Output Recorder”) in 1954. The 740 express just how
big the demand for graphics was, and how minimal a capability was considered meaningful. The
740 was a cathode ray tube to which a camera could be attached. Digital-to-analog converters
drove the cathode ray tube, slowly drawing lines, based on the digital outputs of the computer.
This method gradually came to be known as “vector graphics,” to distinguish it from other
technologies.

Figure 1.7: An IBM Model 701 with Model 740 Cathode Ray
Tube Output Recorder

Lines were plotted one point at a time. IBM justifiably boasted (at the time) that points were
plotted at a rate of 8,000 per second, with a display accuracy of a given point of only 3%, but
with good repeatability. You could not constantly scale the resulting image, but the image would
have at least conceptual value.
Typically, the camera shutter was opened when the drawing started, and closed when it finished.
At that time, the film could be developed, and the image could be viewed later the same day.
Needless to say, this tech was not suitable for playing video games. Of course, one could maintain
a simpler image on the display simply by repeating the drawing instructions at a fairly high
rate. But this used most or all of the CPU time, and limited the detail which could be drawn.
The 740 had a sister display, the 780, which had a long-persistence phosphor (20 seconds). While
not as precise, when paralleled with the 740, it allowed the operator to verify that the image

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