VIDEOFACE TO FACE

Going all dotty on digitisers a couple of issues back led Franco Frey to fame, recognition but no fortune. Not that anyone mistook him for Lesley Anne Down or Marlene Dietrich, but the arrival of a small parcel covered in Dutch postage stamps showed him that Big Brother is watching and reading.

Thinking about late Christmas presents, he unpacked the gift. He didn't find After Eights or Black Magic, but an insignificant looking black box... immediately recognisable as a Spectrum add-on. In fact, it was of the variety of video digitisers, previously rare and unknown creatures, now suddenly popping out of all sorts of nooks and crannies.

VIDEOFACE

Producer: DATA Skip
Retail Price: £69.00 inc VAT/P&P

One quick look at the manual reveals a great deal about the author's English, but little about the Videoface. After the usual prod and thrust, the interface was married to my now not-so-new Spectrum Plus, which has developed the disturbing habit of violently rejecting incompatible interface partners. Not so in this case. The Videoface should happily co-exist with such venerable species as the Spectrum 16K/48K, Spectrum Plus, 128 and Spectrum Plus Two, although experiments were not made to prove all these bold statements!

Clearly, Videoface is not going to perform unless it is connected to a video camera or at least a video recorder... as no hardware was supplied to make the connections, I pinched a competitor's accessory left over from an earlier review and made the appropriate connections. As life isn't worth living without software, I loaded up a short program from the tape supplied with the unit and thanked God it wasn't recorded in Dutch...

The menu reveals the most outstanding feature of Video face - animation. Could this really be? Was this the breakthrough that everybody had been waiting for? Was Marlene Dietrich going to perform on the Spectrum?

Optimised on speed and the result is a conversion period of only 16 non-interlaced TV screens, which means a scan speed of only 320 milliseconds. At this rate, over three digitised screens can be generated per second, which takes the user into the realm of animation. The effect is quite staggering, considering the massive limitations of the Spectrum.

Choosing the right subject is the main problem, as two aspects have to be carefully considered. One is the low resolution of the Spectrum screen - so avoid pictures with too much detail. Go for close-ups and uncluttered screens. Secondly, avoid fast moving sequences: consider that the old 8mm home-movie cameras operated at 18 pictures per second - still six times faster than the Videoface - and you start realising the limitations. Try to avoid panning shots or zoom movements. As the digitised picture is generated over a period of 16 TV pictures, any major change or movement creates a distorted and meaningless digitised end product.

MARLENE DIETRICH LIVE FROM THE BLUE ANGEL

The video screen consists of 625 lines and for a flicker-free display, it is scanned 25 times a second. In the days when standards were laid down, the frequency of the picture signal was seen to be beyond the limits of technology, with the high line resolution and 625 lines. It was decided to divide the full screen into two consecutive scans of 312.5 lines, with the first scan defining 'odd' numbered lines and the second defining the 'even'. The two scans give an interlaced display of 625 lines when viewed by the human eye.

Most computers do not have interlaced displays, and theiro maximum resolution is only 312 lines or less. This means that if an individual half-screen is to be digitised and stored, it must be done within 20 milliseconds. To be able to record an individual TV frame, a very fast analogue-to-digital converter is required (a flash A/D converter) which measures the voltage level of the video signal and converts the value into a binary number ready for storage in memory. The main problem is that these converters cost an arm and a leg. That's alright for special effects as seen on Top Of The Pops, where the video editing system works with full resolution screen storage to provide fantastic screen manipulations, but it's not so good for home computers.

'Home' digitisers work with slow A/D converters which require a frozen picture, as the conversion of the screen requires several scans and can last up to several seconds. The SUNSET digitiser reviewed a couple of issues back took nearly six seconds, but stored each point as a nibble - a half byte - giving a grey scale from 1 to 15. When displayed on the computer screen, the black to white boundary could be set anywhere between 1 and 15. Furthermore, using up to three different stippling effects. a grey scale effect could be arranged, giving a remarkably lifelike image despite the low resolution.

With Videoface DATA SKIP optimised on speed and the result is a conversion period of only 16 non-interlaced TV screens, which means a scan speed of only 320 milliseconds. At this rate, over three digitised screens can be generated per second, which takes the user into the realm of animation. The effect is quite staggering, considering the massive limitations of the Spectrum.

Choosing the right subject is the main problem, as two aspects have to be carefully considered. One is the low resolution of the Spectrum screen - so avoid pictures with too much detail. Go for close-ups and uncluttered screens. Secondly, avoid fast moving sequences: consider that the old 8mm home-movie cameras operated at 18 pictures per second - still six times faster than the Videoface- and you start realising the limitations. Try to avoid panning shots or zoom movements. As the digitised picture is generated over a period of 16 TV pictures, any major change or movement creates a distorted and meaningless digitised end product.

CAMERAS ROLLING?

The modus operandi is quite simple. Pressing the Q key initiates the picture scanning and Videoface deposits six screens. In rotation, within a defined screen buffer area of memory. Videoface also displays the screens on the Spectrum and the animation effect can be studied. As the Spectrum screen is limited to 256 by 192 pixels, the entire TV screen can't be fitted into the digitised format - the digitising frame may be positioned anywhere on the TV screen, using the cursor keys.

When you're satisfied with the last six displayed screens, pressing the Z or SPACE key interrupts the scanning operation and the last six screens are retained intact within the buffer memory. They are now available for display by single-stepping or for animation at variable speed. The rate of display can be stepped up to create a quick motion effect. The screen on display can be copied or saved to tape.

As far as speed is concerned, the Videoface clearly knocks pixels off the SUNSET digitiser. But all is not well. The digitised screen is stored on a pixel basis in memory, and grey scaling values are lost forever. The trigger point between black and white is controlled by hardware, and is adjusted by twiddling a potentiometer knob on the interface during conversion time. Once material has been stored, changes can't be made - stippling effects can't be generated.

The net result is a comparative loss in picture quality. A picture captured by SUNSET'S equipment with grey stippling effect can be much better than a Videoface-generated picture. So it's take your pick - animation or improved picture quality? Videoface is fun to use, but it has some peculiar quirks. It is quite annoying to have the mini-menu blinking over the picture you're trying to view when using the single-step mode. A more serious matter is that the program does not seem to be crash-proof. In fact, whenever a picture is saved to tape the program decides to go off on its own and leave the operator in a slightly animated state - especially when the intention was to save all six screens to tape! Naturally, the only solution is to reset the computer and lose the contents of the screen buffer.

Similarly, during conversion the program has been known to wander off. It happens to the best of us ... The software consists of a mixture of BASIC and machine code that takes up about 1300 bytes starting at location 63232. The area between BASIC and machine code can only be used by switching animation off (an option in the main menu), otherwise this area is used to store the six screens.

The manual lists Videoface compatible interfaces which can be operated without interference.

CONCLUSION

A very enjoyable add-on for the Spectrum, which can provide hours and hours of entertainment. I still haven't found any serious use for a digitizer, but that, to my mind, is not very important. Make sure you have a video camera or a video recorder with a good still frame facility if you're after good still shots.

I'll end by quoting the excellent manual, which sums up all aspects of the Videoface in a short and concise way: Now you can using the DATA-SKIP Videoface pour signal from the analogue world into a digital dress.

Interested image-grabbers can acquire the Videoface from DATA SKIP, Lange Willemsteeg 10, 2801 Gouda, Holland

RAGE HARD!

Introducing the new YS hardware page, featuring Technical Ed Phil Snout on oscilloscope and magic screwdriver. This month he takes apart a pair of video digitisers, the Rombo VIDI-ZX and the Dataskip Videoface.

Video frame grabbing used to be the province of more sophisticated computers, with the interfaces costing from £90 to around £500 for some of the biggies. But even on the Spectrum it's possible to grab frames from video and manipulate them, and indeed use them in your own program as you would any other SCREEN$ file. There are currently two brands of digitiser on the market at the moment, and both of them are relatively inexpensive.

Although we are comparing these two devices head-to-head, it would be unfair to compare them too closely. As in anything, it's what you prefer on a personal basis and whether or not it fits your needs, which in the end will dictate what you'll buy. I prefer to tell you the merits of both and let you make up your own mind. But as comparisons must be drawn, for what it's worth. I'll give you my verdict at the end. Okay, let's plug in the video and see what develops.

DATASKIP VIDEOFACE

Readers will no doubt be familiar with the name Dataskip Videoface, as they've been advertising for some months under their own name. But now they're doing a deal with Romantic Robot, and the Videoface has been re-launched in a new box. The device comes with a software cassette and a manual; or more accurately a sheet of paper, explaining how to use it.

One of the main features that struck me about this device, 'cos I saw it first in prototype about a year ago, is that as well as being stuck in a new box, the software that goes with it has been re-written, adding a couple of new features. The device scans the TV picture at six frames a second, and stores the preceding six after you press the frame grab button. So, main additions are the facility to save from one to six frames at once, and animate them at any speed. This can be very handy for making videos, giving you access to Max Headroom style digital effects, and enabling you to set up sequences which repeat over and over again.

To use the unit, you plug one end of a lead into the BNC plug marked 'video out' on the back of a domestic video player, and the other end into the photo or RCA plughole on the digitiser. Then you load the software, and the picture from the video comes out on your monitor, via the Speccy. When you spot a piccy you like on the screen, you slap the SPACE bar and the image is frozen or 'grabbed,' and prepared for animation or saving to tape/disk. You can step through the six screens in the frame buffer to select the best one, before saving one or more of them.

I must admit, I found the manual a bit insubstantial and a trifle difficult to understand, but as it was, I presume, written by the Dutch bloke who designed the machine, I s'pose we can't be too harsh. It does raise a few interesting questions, though. Like, nowhere does it say what the red LED does, and this was a bit of a problem at one point as the red light was on and no picture was forthcoming on the Speccy screen. Hmm. Still, this had stopped by the time I booted it the next day, so your guess is as good as mine as to what was going on there.

On the plus side, the animation is pretty smooth, flipping those six screens without very much flicker at all. It would have been better to see more instructions about how to use those six screens in your own programs though. There isn't a grey tone as such, but the machine cheats it in the way it bleeds out in areas which offer neither black nor white. The effect is a bit erratic, but as you can see in our piccy of Spock, it can be quite effective. A bit of judicious gain twiddling usually manages to get a good balance for most source screens. The best results apparently, are to be had from colour video signals, but it says in the manual that you can use black and white as well... although quite where you'll get a black and white video source anyway, I wouldn't like to say.

The Videoface is a nicely put together bit of kit, and all the additions to the software work well.

VIDI-ZX

This is a really new device which has a nice home-built look to it, being housed in what looks like an electronics project box, with a Rombo sticker on the top. The edge connector and the PCB sticks out of the bottom of the box, but although it looks as though it might be a bit wobbly when plugged in, it actually seats itself quite firmly.

Once you're all connected up, the free cassette of software is then loaded and you're presented with the fast 10 frames per second display. On the top edge of the screen is a menu with (G)rab, (S)hades On, (V)iew, and (M)enu written on it. When you see a frame that you like, just press G, then the screen is frozen ready to be saved. Grab then changes to (R)un, so if you don't like the screen you've grabbed, you can start again by pressing R. You shift menus with M and are presented with one that says (L)oad, (S)ave, (C)opy, (M)enu, and their use is obvious. View is an option for turning off the menu so you can see the whole screen.

By far the most interesting thing about this interface, apart from its nippy 10fps speed, is the Shade option. This turns on a proper grey tone, a sort of stipple effect, which gives you a flat grey tone as well as black and white on the output screens. This is a very pleasing effect, and so fast! It's the speed of grabbing and the stipple effect that makes the VIDI-ZX such an interesting proposition.

The manual is still not very big, but this one is well written, and told me at some points, more than I really wanted to know about the machine. There's also a useful troubleshooting section, and telephone number to call for technical support. Oh yes, on the back of the unit there's a little orange plastic link pushed onto the top two of three small pins which protrude from the PCB. This link reconfigures the machine for use with the DISCiple, and the DISCiple uses address line 6, which is also used by the VIDI-ZX. Moving the link from the top two pins to the bottom two, will change the VIDIs control to address line 4, allowing use of the DISCiple. An additional program, called VIDI4, is featured on the software cassette to run the machine from address line four.

Full details of the driver software are given in the manual, so that anyone can use the VIDI with their own programs along with full details of the machine code. Plus, all the appropriate addresses in memory are labelled and annotated so you can design your own software if necessary. No operational problems or bugs showed themselves whilst the unit was being tested. In fact the few things that did go wrong were well error trapped. When I put in a filename too long for the string handler for example, the program broke out of Basic to tell me 'Invalid filename'. On a badly worked out program, this would have been the end of civilisation as we know it. But not only didn't the machine reset my Speccy, but the picture I'd grabbed stayed in memory for some minutes while I sorted myself out. All I did was to press RUN and ENTER, and I was back where I started again.

The VIDI-ZX is a first class bit of kit, and seems reliable and well set out. Highly recommended.

(Snouty Star Trek Note: THe veteran Trekkers among you will recognise the episode of ST I used for this experiment. It was of couse 'Obsession'. What a corker that was!)

WIRED

YS presents a handy-dandy guide to having fun with your peripherals. And who better to lead us down the hardware path than JON PILLAR? Quite a lot of people to be honest, but they were all at lunch.

There's more to life than playing Speccy games. Using Speccy hardware is also to be recommended. Over the years a huge number of little black boxes have appeared for plugging into the back of everyone's favourite, um, little black box. Sadly, a lot of these have now gone forever. The Specdrum, the Slomo, the Music Machine... where are they now? Actually, they're still around, you just have to look rather hard for 'em. For those of you who can't be bothered looking rather hard, there are still plenty of goodies to be collected.

VIDEOFACE DIGITISER
Romantic Robot/£29.95

Who could resits the opportunity to grab pictures from the TV and deface them artistically? The Digitiser is one of those completely useless items that has found a place in the heart of every Speccy owner. Grabbing in real-time, or just watching a programme via the grainy resolution of a Speccy screen is curiously compulsive. To put it simply, the Digitiser is an essential purchase. It's just that nobody can quite figure out why.

IT'S ALL GOING HORRIBLY WRONG DEPARTMENT

Speccies are like mushrooms. If you keep them warm and nurtured, they flourish. But if you trample them into the ground or allow your dog to eat them while walking in the woods, they tend to fall over. Furthermore, I wouldn't recommend that you put them in a pan and cook them with a nice free-range egg in an attempt to make a mushroom omelette, because it won't work. Um, actually, Speccies aren't like mushrooms at all. Forget I said that bit.

Anyway. The point I'm failing quite spectacularly to make is that Speccies are temperamental beasties. Inevitably, they'll break down. And while the most sensible course of action is to take your ill machine along to an authorised repair centre, you can fix some things in the comfort of your own home. But be sure to have a responsible adult on hand. They will then say, "I told you that you should have gone to an authorised repair centre," in a patronising tone of voice when you bodge the job and wreck your Spec. If you feel up to the task though, quite a few companies offer Speccy spares - everything from new ROM chips to new +3 disk drives. WAVE are particularly well-endowed with small bits of Speccies. Their catalogue has just about everything you need to build your own machine! Buy the spares direct, put them aside for that fateful day, and it'll be cheaper to repair your Speccy yourself. Or else get your local soldering iron whizz to do it for you. Just don't say we didn't warn you if things go even more horribly wrong.

Well, that's it. Hopefully this little trip through hardware land has been useful and informative. If not, why should I care? I'm off to digitise the climax of The Terminator and save it out to disk as an animated sequence. Just don't tell anyone, or they'll all be at it…