Search found 279 matches

by Richard Russell
Thu Jul 05, 2018 7:47 pm
Forum: emulators
Topic: Beebem Mode 7 glitch
Replies: 37
Views: 1044

Re: Beebem Mode 7 glitch

Does anyone have an actual BBC to test the conceal / hold graphics interplay? Does the conceal code have priority over the hold graphics code? I posted a photo of the testpage on a real BBC Master above (it was originally a Master 512 but the internal co-processor has been removed): you can see tha...
by Richard Russell
Wed Jul 04, 2018 1:16 pm
Forum: projects
Topic: Viewdata Service
Replies: 56
Views: 2723

Re: Viewdata Service

Excellent news, cheers Richard. I will await developments. I have today released my client software for the TELSTAR service (and other Viewdata-style services accessed via telnet, such as CCl4). Rather than making it available separately, I've bundled it with the latest update to BBC BASIC for SDL ...
by Richard Russell
Tue Jul 03, 2018 8:59 am
Forum: general
Topic: "Outline specification for the BBC MICROCOMPUTER system"
Replies: 199
Views: 16040

Re: "Outline specification for the BBC MICROCOMPUTER system"

the IBM PC being available in the same year the spec was distributed to manufacturers The specification was distributed to manufacturers at the end of 1980, whereas Wikipedia says the IBM PC was announced in August 1981. it seems pertinent to ask why the BBC didn't consider it - or did they? It did...
by Richard Russell
Mon Jul 02, 2018 11:03 pm
Forum: projects
Topic: Viewdata Service
Replies: 56
Views: 2723

Re: Viewdata Service

Is there any viewdata terminal client software available that runs natively on Windows, rather than on a BBC or in a browser? I've recently written a suitable client in 'BBC BASIC for SDL 2.0' (BBCSDL) which runs in Windows, Linux, Mac OS, Raspberry Pi, Android and iOS. I was hoping to release it s...
by Richard Russell
Mon Jul 02, 2018 6:28 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

Ahh, but most computers in the 1970s, 1980s and 1990s don't actually produce a proper interlaced output. Most, perhaps, but of course it was a requirement from the start that the BBC Micro must be able to generate a 'broadcast compatible' interlaced output so it could be fed as a source into the st...
by Richard Russell
Mon Jul 02, 2018 6:24 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

But isn't 15fps an odd frame rate for UK TV also? Some of the recovered material had already been standards-converted to 'NTSC' and apparently couldn't be located in its original PAL format. In that case it's better not to perform another conversion back to 25 fps, which would make the quality even...
by Richard Russell
Mon Jul 02, 2018 8:20 am
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

Surely that depends on what the source is. I haven't got to the bottom of why the source material wasn't available from the BBC's archives, and in some cases had to be taken from poor quality copies on VHS and YouTube etc. One message I received from the team referred to these as having been 'place...
by Richard Russell
Mon Jul 02, 2018 8:04 am
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

I had put down the fact it looked like it had been encoded on a potato down to my poor internet connection and I was viewing it at the lowest possible quality. Are you saying it looks that bad for everyone? I'm pretty certain everybody gets the same stream; AFAIK the material was only encoded once....
by Richard Russell
Sun Jul 01, 2018 7:12 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

Does that make it one of those filters that performs rather better on pictures at the expense of performance on text? Do you mean scrolling text (such as film credits)? If it's scrolling at an 'unfortunate' speed it may break any non-motion-compensated de-interlacer. Just one of those things, but a...
by Richard Russell
Sun Jul 01, 2018 4:12 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

BigEd wrote:
Sun Jul 01, 2018 2:00 pm
Edit: hang on, I'm thinking of 3:2 pull down... should be regular but isn't always.
24 fps (film) input and 29.9700299700... fps (NTSC TV) output would result in an irregular pattern. I don't know whether they try to be that precise with 3:2 pulldown.

Richard.
by Richard Russell
Sun Jul 01, 2018 1:56 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

I certainly hadn't considered the complication of that having been lost and the two options for how the source would be presented after simplistic digitisation. It's not so much "digitisation" since 'real-time' digital formats (such as 'SDI') preserve all the timing information that was present in ...
by Richard Russell
Sun Jul 01, 2018 1:31 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

The conversation systems that do a exist best guess based on the line above, the line below and the relevant lines in the adjacent frames. I think it's rather misleading to call it a "guess": it's more scientific than that! Below I've shown two slices through the vertical-temporal spectrum of Marti...
by Richard Russell
Sun Jul 01, 2018 1:18 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

how far wide of the mark would I bet in suggesting that a de-interlacing step would be to know whether the field concerned is odd or even, interpolate the missing lines from the ones present so the video is now 50fps at the full vertical resolution and then process further as desired? It depends on...
by Richard Russell
Sat Jun 30, 2018 10:36 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

You mean that wibbly-wobbly effect in movement and other crumbly bits and pieces? Anything moving breaks into pieces, yes. Somewhere along the line somebody has done something stupid (perhaps scaling without de-interlacing first, as was suggested), but whether that was before CLPA got hold of it, a...
by Richard Russell
Sat Jun 30, 2018 9:06 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

If you want an example of poor video quality, take a look at 'Making The Most Of The Micro' Live (in full screen for the full horror). It has dreadful motion artefacts; on Facebook they are described, by somebody well qualified to comment, as "wobbly edged motion (interlaced content scaled as progre...
by Richard Russell
Sat Jun 30, 2018 1:12 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

For years, I never bought one of the earlier tellies after CRTs were stopped because I hated the look of them. The picture just looked too gungey. Limitations in early flat screen display technologies (and to some extent in how the video was compressed for broadcast) have no bearing on the quality ...
by Richard Russell
Sat Jun 30, 2018 12:58 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

PitfallJones wrote:
Sat Jun 30, 2018 10:22 am
It's great the BBC had kept them all - I was imagining they were lost in time after all these years!
I don't think it was the BBC, my understanding is that Steve Lowry found them on floppy in his loft. Ian Trackman, who wrote most of those programs, was at Wednesday's launch.

Richard.
by Richard Russell
Sat Jun 30, 2018 9:44 am
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

for 80s television programmes, I think 25p is very forgiving. I would say that's very much a minority point of view! Imposing 'film motion' on something originally shot on 50i video will cause many people (including me) much discomfort, and of course it means the performance of the deinterlacer is ...
by Richard Russell
Fri Jun 29, 2018 10:40 pm
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

It's not often you get quality akin to the master tapes when looking up these BBC videos, so I say to all of us - grab 'em and archive 'em. Sadly the quality is variable and AIUI everything is 25p not 50p, so motion and de-interlacing artefacts are the norm. Apparently some of the material was sour...
by Richard Russell
Thu Jun 28, 2018 3:00 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 517

Re: Expanding BBC BASIC on Acorn 8 bit machines

Otherwise, going to the end of a line is easy (because of the line length byte). Do Sophie's BASICs 'remember' the line length byte then? In mine I don't (indeed I don't even see it if I've arrived on the line via a GOTO or PROC call etc.) so to find the end of a line, e.g. when processing a REM, I...
by Richard Russell
Thu Jun 28, 2018 1:23 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 517

Re: Expanding BBC BASIC on Acorn 8 bit machines

I know line number encoding works similarly, although it bends over backwards to keep the encoded number in ASCII range, but I don't think there's any particularly good reason for that, or at least no limitation that can't be worked around. The reason is so that 'forward searches' (such as to find ...
by Richard Russell
Thu Jun 28, 2018 12:55 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 517

Re: Expanding BBC BASIC on Acorn 8 bit machines

But the issue is you still need to put it somewhere. I'm suggesting that the maximum length of a string should be determined by available memory, not by the size of a fixed-length statically-allocated 'string accumulator' (which is itself wasteful of memory). plus creating a new string variable typ...
by Richard Russell
Thu Jun 28, 2018 11:43 am
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 517

Re: Expanding BBC BASIC on Acorn 8 bit machines

64K strings on an 8-bit processor is very difficult as you need somewhere to put a 64K string accumulator.... So how exactly do you think BBC BASIC for Windows and BBC BASIC for SDL 2.0 support 32-bit-length strings? Do you imagine they each have a 4 Gbytes 'string accumulator'? (For the avoidance ...
by Richard Russell
Thu Jun 28, 2018 8:29 am
Forum: general
Topic: BBC releases computer history archive
Replies: 90
Views: 1830

Re: BBC releases computer history archive

Here is an iPlayer Radio link to the piece in yesterday's PM programme about the launch (available in the UK for another 29 days at the time of posting).

Richard.
by Richard Russell
Thu Jun 28, 2018 8:28 am
Forum: general
Topic: "Outline specification for the BBC MICROCOMPUTER system"
Replies: 199
Views: 16040

Re: "Outline specification for the BBC MICROCOMPUTER system"

I see the recently released archive of BBC TV programmes from the Computer Literacy Project has both Sir Clive Sinclair's allegations on the bidding process and John Radcliffe's response Fred Harris, who did the interviewing, was at yesterday's launch! I can personally confirm what John Radcliffe s...
by Richard Russell
Wed Jun 27, 2018 10:00 pm
Forum: software: other
Topic: Expanding BBC BASIC on Acorn 8 bit machines
Replies: 21
Views: 517

Re: Expanding BBC BASIC on Acorn 8 bit machines

To be honest I think a lot of what I wanted was actually in BASIC V The main thing I couldn't live with in BASIC V is strings limited to 255 characters, and it's interesting that Brandy (which in most respects matches the BASIC V spec closely) increased this to 65535 characters - or should I say by...
by Richard Russell
Wed Jun 27, 2018 8:30 am
Forum: off-topic
Topic: Using BBC BASIC to teach programming concepts in 2017
Replies: 82
Views: 2233

Re: Using BBC BASIC to teach programming concepts in 2017

Nothing is quite as "in your face" and attention-grabbing as a black screen. No "nasty" GUI to distract anyone. As I pointed out previously, BBCSDL doesn't of itself have a GUI, and white on black is just a trivial change to the palette. Replace the supplied 'bbcsdl.bbc' with this custom version an...
by Richard Russell
Tue Jun 26, 2018 4:28 pm
Forum: emulators
Topic: Beebem Mode 7 glitch
Replies: 37
Views: 1044

Re: Beebem Mode 7 glitch

What's your take on the different contents of row 06? Obviously I wouldn't choose to use the 'alternative' version on a genuine Beeb or a MODE 7 emulation because the SAA5050's interpretation of the held graphics rules (wrong according to the later spec, but not at the time) makes it look ugly. But...
by Richard Russell
Tue Jun 26, 2018 1:59 pm
Forum: emulators
Topic: Beebem Mode 7 glitch
Replies: 37
Views: 1044

Re: Beebem Mode 7 glitch

it was from the sources I could find, I'd have definitely just used yours if I'd seen it I think (and hope) that the only difference between the version that comes with my Test Card Generator software (in 'teletext.car') and the version that comes with BBC BASIC (in 'mode7dem.car') is that the latt...
by Richard Russell
Tue Jun 26, 2018 8:51 am
Forum: emulators
Topic: Beebem Mode 7 glitch
Replies: 37
Views: 1044

Re: Beebem Mode 7 glitch

It doesn't happen to be a test case for the SAA5050 hold mosaic hardware bug unfortunately so a separate test is required to check emulation of that. I think it's a bit harsh to call it a "hardware bug" because it's a perfectly reasonable interpretation of the specification as it existed at the tim...