Digital Imagizing, Part 2

Hopefully by now you have assembled the hardware involved in this project and have obtained the necessary driver software from the club library. The software I have written allows you to do high-contrast scans, grey-scaling (the combining of several images giving one picture with varying shades of grey representing the different colours), cleaning of noise in the image, flips, inversions, and cut and pasting from one image to another. If you have not yet obtained this software, I have included a short machine code program that will allow you to capture some high-contrast scans.

Before actually trying out the software, you can check the operation of the hardware with a short basic program. Type in the following:

10 OUT 0,255 
20 POKE 23692,255: PRINT IN 0;" ";: GOTO 20

RUN the program and hook up your STILL video source to the digitizer. Now try turning the BRIGHTNESS and SYNC knobs to various positions. You should get four different numbers in a random order. Usually they will be from 252-255. If you get this then the hardware is more than likely in working condition.

Now load the driver software. Either load the version from the club library or type in the one in this article. If you have the good version, the rest is easy. Just choose option #1 and turn the SYNC knob until the message reads ‘IN SYNC’. Now choose a capture option and start digitizing!

If, however, you are using the version printed here, you will have to sync your video source “by hand”. Connect your video source and RUN the program. Turn the SYNC and BRIGHTNESS knobs until you see a picture starting to form from left to right. If the picture is totally black or totally white, adjust the BRIGHTNESS knob accordingly. If the picture freezes or goes too quickly (shorter than 5 seconds), adjust the SYNC knob. For now this will be more or less trial and error. After this step is completed and you can see the picture from your video source on your 2068 display, you have a working video digitizer!

How does it work? Well, first you must understand TV’s a bit. A picture on a TV starts forming from the top left corner and works its way across to the right corner and then returns to the position immediately underneath the top left and so on until it reaches the bottom of the screen at which time the process restarts. A 2068 is not fast enough to collect all this information at once so it only grabs one vertical line of data from each frame. Since there are 60 frames a second and we need 256 lines, this process requires about 5 seconds. There is of course much more to it than this but that is basically it.

The SYNC knob is necessary because of the varying signal strengths from different video sources. Once you have adjusted it for your particular video source, it should not have to be touched again unless you switch to a different source.

The STRECH knob allows you to compress or expand the image. This is done by changing the sampling rate to a slower or faster rate and allows greater detail to be captured.

The BRIGHTNESS knob determines the amount of black or white in the picture. The brightness can also be controlled by software by setting bits 0,1, and 2 of port 00 to a value from 0-7 using binary. Resetting bit 4 restarts the timer in the digitizer. This must be done before each capture. Reading bit 0 provides synchronization information and reading bit 1 gives the actual data for the picture, a one meaning black and a zero meaning white.

I am presently working on some software that will provide 512 by 192 resolution as opposed to the current 256 by 192. This should also be printable on a real printer in the same resolution as well as viewed on the screen.

If you are having difficulties with your digitizer or have questions to ask, feel free to call me. Happy digitizing!

5 REM DIGITIZER LISTING by Eric Michaud
10 CLEAR 38911: LET t=0
20 FOR x=38912 TO 39423
30 READ n: POKE x,n: LET t=t+n
40 NEXT x
50 IF t=49564 THEN GO TO 100
60 PRINT "Error": STOP
100 RANDOMIZE USR 39296: BEEP .01,30: GO TO 100
3000 DATA 0,64,0,65,0,66,0,67,0,68,0,69,0,70,0,71,
32,64,32,65,32,66,32,67,32,68,32,69,32,70,32,71,
64,64,64,65,64,66,64,67,64,68,64,69,64,70,64,71,
96,64,96,65,96,66,96,67,96,68,96,69,96,70,96,71,
128,64,128,65,128,66,128,67,128,68,128,69,128,70,
128,71,160,64,160,65,160,66,160,67,160,68,160,69,
160,70,160,71
3010 DATA 192,64,192,65,192,66,1 92,67,192,68,192,
69,192,70,192,71,224,64,224,65,224,66,224,67,224,
68,224,69,224,70,224,71,0,72,0,73,0,74,0,75,0,76,0,
77,0,78,0,79,32,72,32,73,32,74,32,75,32,76,32,77,32,
78,32,79,65,72,64,73,64,74,64,75,64,76,64,77,64,78,64,
79,96,72,96,73,96,74,96,7 5,96,76,96,77,96,78,96,
79,128,72,128,73,128,74,128,75,128,76,128,77,128,78,128,79