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Secret colours of the Commodore 64

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Re: Secret colours of the Commodore 64

#91

Post by boomlinde »

TazeTSchnitzel wrote: post #68
ghusbands wrote: post #66

Earlier quoted context omitted.

No, the signal indicates whether a given field is for even or odd scanlines. I used plenty of computers and CRTs around that time and not one incorrectly displayed progressive as interlaced.

To clarify, I'm talking about CRT TVs, not computer monitors. The latter aren't (usually†) interlaced. †There's some interesting exceptions!

Neither are most CRT TVs, if you keep feeding them the odd/even field repeatedly. I keep CRT TVs and monitors at home and can easily verify this. The effect is usually dark gaps between the lines or doubled lines (where the corresponding field would otherwise have been drawn). Doubled lines, as in the same as the previous line of the same field, not from the previous field. It's not a particularly obscure subject or uncommon trick, so I don't see why you would keep insisting that it isn't so when any source that possibly could have proven you right, if you were, will prove you wrong.

Re: Secret colours of the Commodore 64

#92

Post by TazeTSchnitzel »

ghusbands wrote: post #90
TazeTSchnitzel wrote: post #68

Earlier quoted context omitted.

To clarify, I'm talking about CRT TVs, not computer monitors. The latter aren't (usually†) interlaced. †There's some interesting exceptions!

I'm talking about televisions and similar. You are still simply wrong. Nearly all of the 8-bit and 16-bit consoles and computers that output to CRT default to non-interlaced, without the TV alternating fields. Look at other responses in this thread to see how interlacing used to be achieved and the flexibility it had.

Ah, I see now. Your comment about the half-length scanline made me understand.

Re: Secret colours of the Commodore 64

#93

Post by dirtbox »

anjc wrote: post #70
dirtbox wrote: post #41

Earlier quoted context omitted.

There's even a new speccy coming out. http://www.specnext.com/

Niceee. I wonder if it has a real Z80 or it's implemented on an FPGA as mentioned.

As I understand, the FPGA is to interface the Z80 with the raspberry pi that's onboard to include extra graphic modes and HDMI output, but I could well be wrong. There's a lot of unanswered questions about its inner workings, but they have some good looking test boards already etched.

Re: Secret colours of the Commodore 64

#94

Post by mikejmoffitt »

TazeTSchnitzel wrote: post #50
mikejmoffitt wrote: post #10

Earlier quoted context omitted.

That isn't quite correct. The C64 outputs a progressive-scan image, which is a hack on top of NTSC or PAL. In this configuration, there are only even or odd fields, which double-strike the same area. Thusly, it is 60 fields per second, and since only one field forms the full frame, it's 60 frames per second as well. There is no scanline striping; that is strictly an artifact of poor NTSC capture devices (like most HD…

A progressive-scan image emitted as an interlaced image results in, well, an interlaced image. That the scanline pairs are usually identical merely means that it's wasting vertical resolution. And nonetheless a CRT from the time would show these as different scanlines.

No, this isn't correct. The image isn't "progressive" or "interlaced" until the output stage. Whether or not they are identical is secondary to the timings, which is all that matters. If every frame has an integer number of scanlines (and VSYNC begins during H-blank), it's going to be a progressive scan image.

A "CRT from the time" - the things littered around my apartment that occupy a little too much of my time - can easily illustrate the effect I am describing of a progressive scan image without alternating scanline positions. Go grab almost any '90s game console, or have fun with the Sega Genesis, which supports 240p as well as 480i; Sonic 2 uses 480i to fit two viewports into the two-player mode, but uses 240p during a single-player game.

Re: Secret colours of the Commodore 64

#95

Post by mikejmoffitt »

to3m wrote: post #85
TazeTSchnitzel wrote: post #50

Earlier quoted context omitted.

A progressive-scan image emitted as an interlaced image results in, well, an interlaced image. That the scanline pairs are usually identical merely means that it's wasting vertical resolution. And nonetheless a CRT from the time would show these as different scanlines.

Well, alternate fields have a 0.5 scanline offset, so that's sort of true. But you definitely don't see them both at once. Are you sure you've ever used a proper CRT TV? ;) - you can get the alternating effect with LCD TVs, but that's because LCD TVs handle analogue input in a different way. Justifications for this: 0. TV hblank rate is 15,625Hz - at 50 fields/sec, that's 312.5 lines/field, some way short of the 400…

Alternate fields have an offset, but only if the horizontal sync timings make it so. If a machine is built to output a progressive image, there aren't really "fields", or you can consider them "all odd" or "all even" fields. I don't know anything about the BBC micro, but the Commodore 64 outputs a progressive image.

Re: Secret colours of the Commodore 64

#96

Post by mschaef »

eriknstr wrote: post #89
mschaef wrote: post #83

Earlier quoted context omitted.

Synchronous clocks do this too... they've driven by a motor that's designed to work in phase with the electrical grid's frequency. This means they rotate at a fixed speed and can be used as a time base for a clock. From the perspective of the grid operator, however, 50 or 60Hz is not always 50 or 60Hz. A sudden load or a generator tripping offline (to preserve itself) results in a transient slowdown of the frequency…

I previously worked with Unix sysadmin tasks and software development at Statnett SF [1], the transmission system operator (TSO) for the national level of the Norwegian electrical power distribution network, and am currently studying at the university to become an electrical engineer. We started learning about transformers, generators and motors in three-phase systems this semester, so that document is of interest to…

Cool... good luck! (If you ever find an intuitive way to think about reactive power, please let me know... I get it in broad strokes, I've been trying to wrap my head around the details for over 20 years, off and on.)

> I have been told that the nature of hydroelectric power generator installations makes the act of balancing the power system in Norway quite different from what most other countries are dealing with

Hydro has both upsides and downsides. To the upside, they're easily able to respond to changes in demand. It's the difference between opening a wicket gate and adding fuel/air to boil more water, to make more steam, to apply more torque. Hydro can also support stored power.... sometimes you see what are known as pumped storage generators generate 'negative' output. This means they're running as a motor to pump water up a hill. When power is needed they can just drain the water through turbines to generate power.

That said, Hydro also has additional constraints on operation that can be imposed by flood control requirements, reservoir levels [1], environmental regulations, etc.

1] https://wrrc.arizona.edu/drought-diminishes-hydropower

Re: Secret colours of the Commodore 64

#97

Post by to3m »

mikejmoffitt wrote: post #95
to3m wrote: post #85

Earlier quoted context omitted.

Well, alternate fields have a 0.5 scanline offset, so that's sort of true. But you definitely don't see them both at once. Are you sure you've ever used a proper CRT TV? ;) - you can get the alternating effect with LCD TVs, but that's because LCD TVs handle analogue input in a different way. Justifications for this: 0. TV hblank rate is 15,625Hz - at 50 fields/sec, that's 312.5 lines/field, some way short of the 400…

Alternate fields have an offset, but only if the horizontal sync timings make it so. If a machine is built to output a progressive image, there aren't really "fields", or you can consider them "all odd" or "all even" fields. I don't know anything about the BBC micro, but the Commodore 64 outputs a progressive image.

It's definitely interlaced output, though in most display modes the content is progressive (i.e., both fields look the same) - which is a bit of a dumb arrangement, really, since you get all of the flicker and none of the benefit.

Fortunately there's a command to switch it off, and no TV seems to mind displaying 50.08Hz output rather than 50Hz...

Re: Secret colours of the Commodore 64

#98

Post by TazeTSchnitzel »

boomlinde wrote: post #91
TazeTSchnitzel wrote: post #68

Earlier quoted context omitted.

To clarify, I'm talking about CRT TVs, not computer monitors. The latter aren't (usually†) interlaced. †There's some interesting exceptions!

Neither are most CRT TVs, if you keep feeding them the odd/even field repeatedly. I keep CRT TVs and monitors at home and can easily verify this. The effect is usually dark gaps between the lines or doubled lines (where the corresponding field would otherwise have been drawn). Doubled lines, as in the same as the previous line of the same field, not from the previous field. It's not a particularly obscure subject or…

I think I misunderstood the responses I got at first, and I couldn't easily find a source. Now that I do understand, it's quite interesting.

Re: Secret colours of the Commodore 64

#100

Post by mikejmoffitt »

to3m wrote: post #97
mikejmoffitt wrote: post #95

Earlier quoted context omitted.

Alternate fields have an offset, but only if the horizontal sync timings make it so. If a machine is built to output a progressive image, there aren't really "fields", or you can consider them "all odd" or "all even" fields. I don't know anything about the BBC micro, but the Commodore 64 outputs a progressive image.

It's definitely interlaced output, though in most display modes the content is progressive (i.e., both fields look the same) - which is a bit of a dumb arrangement, really, since you get all of the flicker and none of the benefit. Fortunately there's a command to switch it off, and no TV seems to mind displaying 50.08Hz output rather than 50Hz...

Are you referring to the BBC Micro, or the Commodore 64?
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