Pixel aspect Ratio for CPC/PLUS on different monitors.

[MacDeath]

I was wondering what are the actual pixel aspect ratios for the CPCs ?

Does it change whether you are using a Monocolour or colour Monitor, also does it change depending on CPC old or PLUS monitors (or computers) or various CRT TVs ?

Source :
http://en.wikipedia.org/wiki/List_of_common_resolutions

==Mode0 :
This article stats that Amstrad CPC in Mode0 do have 160x200 resolution, whcih is in number a 4:5 ratio, but displayed in an actual 4:3 size... hence a "real" 5/3 pixel aspect ratio.

When we "emulate" (mockups) this we often assume it is a 2:1 ratio per pixel (and multiples) on our modern plasma square pixelised monitors.

==Mode1 :
Usual 320x200 resolutions (CGA, ST, Amiga,C64,n CPC mode1...) are assumed to be as follow :
320x200, storage ratio of 8:5 displayed on a physical 4/3 again, so pixel aspect ratio of about 0,8333... not exactly square at all.

According to the "mode0" aspect ratio (5/3), Mode1 should be "2.5/3" = 5:6

==Mode2 :

640x200 is 16/5 displayed at 4:3 again, "0,417" pixel aspect ratio (rounded, obviously)... which is 5:12.

concerning Mode2, this can be quite tricky after all...let's just stick to a 1x2 ratio after all...  
Still the 5/12 = 0,417 could be rounded to a 4/10 = 2/5 = 0,4.
So magnification could be somthing like X*2 and Y*5 only... would perhaps be a bit more accurate anyway.

hence a 640x200 becomes a 1280x1000.
Same ratio could be usedd for all Modes i guess to ease the magnification...

Mode1 320x200 is magnified x*4 and Y*5 and so on.


Anyway to the Mode1 (almost square...but not at all after all) we may have the choice to choose between 5:6 or 4:5 magnification, 4:5 being an imperfect compromise but actually do-able on smaller resolution monitors.


Ok now.
what about the "overscaned" sizes ?
Do "standard CPC resolutions" actually have a real physical 4/3 ratio ?
What about the PLUS monitors ?

So ZX spectrum (and MSX) used to have "real" 1:1 pixel ratio while CPC is always in "Mode2 like" shaped pixels ?

Then how to display this like it should be on our modern monitors on a modern PC (emulation) ?

a Mode1 picture, to be well displayed with square pixels should be magnified into something like

x =320x5 = 1600
y= 200x6 = 1200
This start to be a big modern monitor. 

on the other hand in order to have a good old overscan fullscreen picture this would be quite huge too...

384x272 (mode1) is a "correct and safe realistic resolution i guess, or is it more like a 384 x256 (safer vertical display zone i guess).

let's do this...

X= 384x5=1920

y= 272x6 = 1632
or
y=256x6 = 1536

To get Mode2 I guess you divide 2 the vertical, to get Mode0 I guess you divide the vertical resolution (magnification wise) so it is good to keep it to this Mode1 emulation resolution.
Mode2 would be "half" magnified though.

So according to various sources, a proper modern monitor with 1:1 ratio pixels should be somewhat "huge".

I tried the same calculus for EGA display (640x350 in a 4:3 ratio) and found out the good monitor to do it should be like 1920x1400.
Sadly the "heavy" use of the overscan but demos for CPC needs bigger vertical display for a CPC use.

on the other end, mockups in more regularly used CPC resolution like the speccy size (256x192...) can be displayed in real ratio emulation smaller on modern square pixelised monitor

x=256x5=1280
y=192x6=1152

a 1280x1152 minimumly sized screen can do it.

4:5 ratio instead ?



"Arkanoid" : the "256x256" sized display (Mode0 so 128x256 or is it 128x272 ?) still need a high vertical resolution, also a large side border will be displayed especially on 16/9 monitors (they are all like this theses days).

Ouch, my "almost square" monitor is actually 1280x1024... not even really enough.


What do you have as PC monitor ? have you ever tried to magnify CPc pictures in order to get the "theorical" real proportions , could anyone of you with a big PC monitor try to post a few pictures to compare between a real CPC and the emulated display side by side (with the same picture diplayed of course) ?

The point is to try to avoid antialiasing or similar method when having those Amstrad graphics "emulated".

There I posted a comparison (as obviously the name implies, d'oh) so we can see.

Do someone know a monitor (modern) that can manage to be small (in inches diagonal) yet with very high resolution ?

Ok, i also posted a mockup of a rescaled Barbarian2 intro picture in 4:5 ratio (instead of 5:6) so it is actually displayable on an average monitor.

the size of the actual picture is supposed to be 160x200 mode0 (= equivalent 320x200).
could someone make a comparison perhaps ?


Another good thing with the Mode0 is that it is actually easy to get a true ratio at a smaller scale.




Op.Wolf :
I also posted a screened from Operation Wolf... This game has a Speccy sized display (128x192 as equivalent to 256x192).


CPC screeners are often in "overscaned resolution" (384x272), with the pixels being upscaled at 2x1 per pixels.
but if you stick to the real display (not counting the border) it is actually easy to respect a good aspect ratio as for Mode0 it is 5:3.


Hence a speccy sized screen (128x192 mode0 = 256x192...) becomes an easy to display 640x576.


A normal CPC mode0 picture would be like this :


128x192 => 640x576
160x200 => 800x600


Full screens:
192x256 => 960x768
192x272 => 960x816




Of course it becomes still larger than the conveniant 384x272 simply used with 1:1 pixel ratio... false and wrong yet practical.

[MacDeath]

Double post just to compare...

My personnal composition resized...

2:1 ratio (magnified, bottom one)) and 5:3 "true" ratio (top one).


I can only recommand you to verify your graphic compositions with this sort of magnification because it can really alter a lot the shapes of geometrical figures (squares, circles...) or get the body proportions clearly altered too...
Mode0 is indeed helped when you don't have fuckhuge monitors for your PC...

I think this would need a CPCwiki page after all.


Also I may have done a few mistakes here and there, so if something seems wrong to you, tell me please so I can correct it. (I'm not good at math)
Per exemple I admit the Modern monitors all have square 1:1 pixels... but this may not be that simple after all.


Also if you are still using an old CRT VGA monitor, I guess it can be different too as those CRT are more flexible concerning pixel re-dimension.

[MacDeath]

Scalings :

in order to respect the Pixel ratio from the real CPC it would be nice to try to respect the following :

Mode1 :

=1:1
good for smaller display possible. At this scale we can't afford to modify the colours and pixels so it is actually the exact Storage Aspect Ratio.

="Zoom 200%"
Magnification x*2 y*2.
the same, at this point we can't afford to modify whatever.

=Zoom 300%
past this point, it is actually recommended to use actually a x*3 and y*4 magnification.

The "error" compaired to the CPC ratio and 1:1 ratio is the same as the error between a CPC real ratio (5:6) and the 3:4 ratio.
=5/6 - 3/4 = 20/24 - 18/24 = 1/6
=1 - 5/6 = 1/6
So instead of doing a "square"  300% magnification, you'd better try a x*3 and Y*4 which is a nice compromise.

=400% zoom.
the same, try the 4:5 zoom if possible.
X*4 and y*5...
This ratio is the closer to the 5:6 "real CPC" ratio possible.

=500% and 600%
Use the good and "perfectly"accurate x*5 and y*6 magnification instead of a "square" 500% or 600%.


Mode0

=1:1
the smaller display possible on our modern monitors, it is the Storage Aspect Ratio.

=2:1 (100%)
it shows the fact mode0 pixels are twice larger than mode1 pixels.

=200%
4pix x 2 pixels ? compact and practical. Would seem logical.
I haven't do the math yet but it should be calculated wheter a 3/2 ratio is closer to 5/3 than a 2...

=> 2/1 - 5/3 = 6/3 - 5/3 1/3 difference
=> 5/3 - 3/2 =  10/6 - 9/6 = 1/6 difference

Actually there is less error factor between the true Mode0 ratio (5/3) and 3/2 ratio than with 2/1 (or 4/2).
Hence a zoom 200% would be betterly accurate (or less false actually) if displayed as X*3 and Y*2 tha, X*4 and Y*2

1/3 > 1/6...
So I can only recommend a X*3 and Y*2 magnification when dealing with mode0 in 200%.

=5:3 (real CPC mode0 pixel ratio)

Fit for 300% or 400 or 500% I guess...
It is a completely accurate Rendition of the CPC pixel ratio and should be tried whenever possible.

For bigger, try to use multiples of the accurates Mode1 magnifications if possible.

Mode2 :

here we are actually limited to the fact we can't do "half pixels" so the smaller scale possible is the "1x2"...

=X*1 and Y*2.

Then you have to stick to most Mode1 magnification where the X*magnification is pair (dividable by 2).
This mode offers the more anoying constraint concerning magnifications and zooms.


Multimode :

You have to stick to the "smaller pixel mode" used for accurate rendition...

Games like Antiriad or Sorcery do mix mode1 HUD and Mode0 Playfield.

=to do it accurately in original CPC ratio, it would need quite a big magnification because mode0's 5/3 scaling is incompatible with mode1 accurate rendition (can't do 1.5 pixels wide...sadly)

=So you can perhaps stick to mode1's X*3 & Y*4 .
The Mode0 part being at X*6 & Y*4.
This is "wrong" but not that much wrong compared to the error in 8x4 pixels for mode0 anyway...

=Mode1 X*4 & Y*5 + Mode0 X*8 & Y*5 is good.

=Mode1 X*5 & Y*6 + Mode0 X*10 & Y*5 is completely accurate but need a quite big Monitor (or one with very small pixels/high resolution)


All these magnifications can seem unpractical... but let's face it...

=a game purely in Mode0 with no effects such as overscan or multimode split screen could really use a "perfectly accurate" 5:3 magnification provided you stick to the displayed field (exclude/neglect the border).

=Most games actually stick to the dire Speccy specs... 256x192 (mode1) or 128x192 (mode0)

As such a modest modern 17" monitor can easily display "largely" magnified windows.

=Demos on the other hand are often trickier, as many multimode overscan wankfest gratify us with their undisplayable nature on Emulator...





Also the graphic artist would surely love those magnifications supported by some utilitaries such as convImgCPC, GraphicWizardCPC, Graphix2, and so on... just to assure he doesn't screw up any scales so he gets bashed at Reset #8 party in 2012 or find out he have to correct all his work because it may suck badly when implemented on a real machine...*



*Yeay, that was me... ouch....  




BTW I opened a topic on the same subject in French at CPCrulez... there it is :


http://cpcrulez.fr/forum/viewtopic.php?f=5&t=4986


Enjoy!




ok, as those magnification can really become quite big... it is recommended to have very big screen and to operate them from a good distance...
Perfect for CPCing a CPC on a home cinema while comfortably on a SOFA at the other side of the room.

[db6128]

==Mode0 :
This article stats that Amstrad CPC in Mode0 do have 160x200 resolution, whcih is in number a 4:5 ratio, but displayed in an actual 4:3 size... hence a "real" 5/3 pixel aspect ratio....

How is using 4:3 valid when you are referring to the bordered image? I thought the border is of unequal length on the vertical and horizontal sides. If so, the internal image with the resolutions to which you are referring would not be in a 4:3 ratio, and none of the other numbers would be accurate.

If not, it is interesting. Especially anything that can make MODE 0's pixels less rectangular! But I think that, if your calculations are correct, the resolutions required to emulate the 'real' pixel aspect ratios are a little bit unrealistic. No reason they shouldn't be available as options if they are confirmed as accurate and someone has the ability and desire to use them, though.
Personally, I tend to find a window most useful, but WinApe seems to only offer 200% zoom, which is only just big enough on a 1600×900 screen.

[MacDeath]

er... could you explain please ?

To be honnest I didn't measured the picture on a real monitor yet... So i stick to those theorical values... are they that wrong ?

this would need a mix of old school measurment and a few equations...


http://en.wikipedia.org/wiki/Pixel_aspect_ratio


Pixel aspect ratio = Display Aspect Ratio / Storage aspect ratio
=> PAR = DAR/SAR

=PAR : the Pixel actual ratio

=DAR : the displayed field, not including the border, or the "interior" dimensions of the border if you prefer, as on CPC to remove the border doesn't affect the actual size of the pixels (for the same video mode of course)
Would be quantified in inches or cm I guess...

=SAR : the "resolution"... ex : 320x200 is "mundane SAR for unmodified Mode1.

So if the 320x200 from the Mode1 is exactly 4/3 ratio...

(4/3)/(320x200) = (4x200) / (3x320) = 800/960 = 10/12 = 5/6.


Concerning the resolution needed by those big magnifications...


To be fair i don't know well the resolutions available on most monitor...
Mine are as follow :


=one 16/10 monitor (17") displayoing 1440x900.
=one 5/4 monitor (17" too, I guess) displaying 1280x1024.


To be fair a game like Barbarian (totally in Mode0 160x200...) could be displayed quite well with a simple  x*5 and y*3 magnification as it would be a 800x600 displayed windows (the rest of the monitor being some sort of "unused Border after all...) but this would not work with Sorcery or Antiriad (multimode mixing Mode1 and Mode0...)


a Speccy sized game in mode1 (there are shit-tons of them) would be like ...


== x*4 and y*5 magnification...


256x192 becomes 1024 x 960... my square monitor would love this...


320x200 or a mix of Mode1 & Mode0
=>1280x1000... it still fit well my "square 17" Flat monitor provided I can simply center the "320x200" windows properly... Still i'm deeply screwed if i want some game with overscan or mode2 perhaps...


I don't care, I can have Barbarian or Pacmania with accurate pixel ratio filling my modern flat monitor !!!
And so on...


Don't know but it may even be possible to get StarSabre on my 1440x900 16/10 flat monitor... with a ratio like x*3 and y*4 (mode1)...




The only thing is to have those re-scalings and re-centerings easy to activate on Emulator...


After all, 75% of Amstrad games use "256x192" sized screen...
24% use 320x200 sized screens... and the rest use custom sized screens, = sometimes verticall or horizontal fullscreen, but somethimes even smaller screens (some spanish games had really small screens you know ?)


And we all know that Demos don't work well on emulators anyway.


Even though we have a few ovescan... many actual CPC monitors failed to display a theorical 384x272 mode1 fullscreen resolution... you know, the "safe display" zone concept...still valid obviously...

[db6128]

To be honnest I didn't measured the picture on a real monitor yet... So i stick to those theorical values... are they that wrong ?

That's what I'm asking. There's every chance I'm wrong because I don't have a CPC here to check, but I did think that the border is larger either vertically or horizontally (can't remember which, so again, I might be wrong). This would mean that the standard resolutions would not be at a 4:3 ratio. Again, someone else would need to confirm. Anyway, I'm just a simpleton who programs in 256×256 : P

[MacDeath]

ok, I switched on my old ctm664 (or 644 ? lol)

So, border whatever, enter...ok i have a clear measurable window...

the monitor seem to be 29x21... as it is not flat nor square this is really an approximative measurement...(what's the word actually ?)
28/21 = almost 4/3... ooooo kay...

Then... the inside of the border...

24x15.5centimeters (hard to do the to the measure precisely...) The Monitor is "cold".

you may be right my friend... Wikipedia don't know shit actually.

Something like 24/15,5...48/31.
looks like a 3/2 ratio actually...(sort of)
perhaps close to 16/9 or 16/10 actually...

So...
I would need to display an overscan checkerboard so it would be easier to count the actual number of pixels really displayed in fullscreen.
Would be good to have comments from other users and to do a lot of Benchmarkings on different monitors...

let's say it displays a 384x264 in 4/3 then (the external dimension of the actual screen)

(4/3)/(384x264) = (4x264) / (3x384) = 1056/1152 = 0,91666... like 9:10 actually in mode1 then ?

Oh shi... my CPC do have square pixels... My whole posts are useless...
I'm a failure.

But I still think the PLUS are slightly different...

[db6128]

you may be right my friend... Wikipedia don't know shit actually.

Probably they weren't accounting for the border and just basing it off slight knowledge that the CPC was displayed on TVs or TV-like monitors. Also, it was lumped alongside two other systems, so they might have just assumed partly or even completely based upon those.

Something like 24/15,5...48/31.
looks like a 3/2 ratio actually...(sort of)

320×200 in 1:1 pixels would be very close to 3:2

[MacDeath]

That's perhaps the problem... so close yet so far...
I guess we should ask peoples to benchmark all this...so we would have a proper statistic on the matter and do a nice CPCwiki page about it then (and correct Wikipedia as well)

[Gryzor]

Oh shi... my CPC do have square pixels... My whole posts are useless...
I'm a failure.

But I still think the PLUS are slightly different...

Ohh boy. Well, if it's any consolation, as far as I could follow the conversation it was very interesting. Also, since you posted that pic of yours, I thought this might make you feel good (taken at my office):


[attach=2]

[db6128]

Two things: the attribution to me in your quote is incorrect, and the post that it's actually quoting, presumably MacDeath's, is not showing for me; neither is at least one other reply that I saw (I think by fano) that came after MacDeath's post where he suggests a benchmark and page.

[Gryzor]

Huhhhh? It's still there... can you take a rolling screenshot of the entire page, assuming you have reloaded?

[MacDeath]

Anyway, could some of you confirm about the size of the 320x200 zone on your real monitors ? does it change (even slightly) with a different CPC ?


Would be nice to have a "mass" benchmarking on the matter ?

[db6128]

can you take a rolling screenshot of the entire page, assuming you have reloaded?

I reloaded a bunch of times, including re-navigating from the index in case the 'latest post'–type suffixes to the URL were doing weird stuff (which I've noticed before, although perhaps that was actually the same thing as this), and I've since shut down, been away, and come back. : P Still the same:

[Gryzor]

Oh man, have no idea what your system is on  Your screenshot does not reveal much (that's why I mentioned a rolling one), but I see all the posts even as a guest...

[MacDeath]

thx to all of you to point out loud when I told I was a failure...




grrrrrr.....

[McKlain]

I reloaded a bunch of times, including re-navigating from the index in case the 'latest post'–type suffixes to the URL were doing weird stuff (which I've noticed before, although perhaps that was actually the same thing as this), and I've since shut down, been away, and come back. : P Still the same:

I would blame it on McAffe 

[Devilmarkus]

Here's the bad quote:

[attach=2]

[db6128]

Oh, OK, so that was edited onto the end of the old post, and I never saw it. I thought it had been a new post. A bit silly! But not too illogical since fano's post has indeed disappeared, so I assumed MacDeath's post had been separate and was also missing. Maybe fano deleted his post?

[fano]

Yep , i deleted my post as i replied MacDeath on a french forum  (and after reading it twice i found it not constuctive enough...)

[db6128]

Phew, I'm not crazy (at least not completely)

[Bryce]

Anyway, could some of you confirm about the size of the 320x200 zone on your real monitors ? does it change (even slightly) with a different CPC ?


Would be nice to have a "mass" benchmarking on the matter ?

Of course it's different on different monitors (not CPCs). The ratio depends on how stretched the picture is, and this can be adjusted with a variable resistor inside the monitor, so every monitor could have a different ratio.

Bryce.

[MacDeath]

Phew, I'm not crazy

of course you are...

Seriously I have the strange habit to heavily edit my post, this explains why they can get that long and somewhat messy.
one of my post may be quite different e few minute after you read it.

It comes from a Warhammer forum I go to where you are not allowed to "double post" too much, so you have to edit your post instead of adding another, unless someone re-post after you.

Ok, Toto did some measures on his own monitor too.

320/23,5 = 13,6
200/15,5 = 12,913,6/12,9 = 1,05
En partant du principe qu'on a une mesure approximative, on est proche d'un ratio 1:1 ...

The good aspect means that the CPC on its native monitor have quite a large border... which while not good when playing "stamp" speccy sized games, can be quite good when dealing with Demos in full overscan.
Some parts of the Batman Demo (the flying chip per example) are really quite impressive then.
The intro pages fromTitus' Knight Force are also quite impressive.

But as the Amstrad PLUS tends to have a slightly different Pixel Aspect Ratio (because different monitor) it really put both machines appart, even if this is quite subtle.

When you deal with large bits of graphics (= overscanned full screen) it starts to be visible.

Another thing to notice is the difference between the center of the screen and the borders or corners... the round shaped corners really eat a lot of pixels actually.

so every monitor could have a different ratio.

Then it would be good to have a few statistics anyway, so we can see the range of margin on those aging hardwares.

[TotO]

In MODE 1, the ratio is 1:1 because the CRTC PAL/50Hz overscan resolution is 4/3 and the CTM tube too.

- 192x288 = 0,66 = 2/3 (MODE 0)
- 192x576i = 0,33 = 1/3
- 384x288 = 1,33 = 4/3 (MODE 1)
- 384x576i = 0,66 = 2/3
- 768x288 = 2,66 = 8/3 (MODE 2)
- 768x576i = 1,33 = 4/3

On a CTM screen you see :

- 192x288 = 2:1 (MODE 0)
- 192x576i = 4:1
- 384x288 = 1:1 (MODE 1)
- 384x576i = 2:1
- 768x288 = 1:2 (MODE 2)
- 768x576i = 1:1